Comfortmaker CHT4A7T Split System 2 Stage Air Conditioner Instruction Manual

C4A7T, H4A7T, T4A7T
SPLIT-SYSTEM 2-STAGE AIR CONDITIONER
WITH R-410A REFRIGERANT
2 – 5 TONS
Installation Instructions

NOTE: Read the entire instruction manual before starting the installation.

SAFETY CONSIDERATIONS

Improper installation, adjustment, alteration, service, maintenance, or use can cause explosion, fire, electrical shock, or other conditions which may cause death, personal injury, or property damage. Consult a qualified installer, service agency, or your distributor or branch for information or assistance. The qualified installer or agency must use factory-authorized kits or accessories when modifying this product. Refer to the individual instructions packaged with the kits or accessories when installing.
Follow all safety codes. Wear safety glasses, protective clothing, and work gloves. Use quenching cloth for brazing operations. Have fire extinguisher available. Read these instructions thoroughly and follow all warnings or cautions included in literature and attached to the unit. Consult local building codes and current editions of the National Electrical Code (NEC) NFPA 70. In Canada, refer to current editions of the Canadian Electrical Code CSA 22.1. Recognize safety information. This is the safety-alert symbol . When you see this symbol on the unit and in instructions or manuals, be alert to the potential for personal injury. Understand these signal words; DANGER, WARNING, and CAUTION. These words are used with the safety-alert symbol. DANGER identifies the most serious hazards which will result in severe personal injury or death. WARNING signifies hazards which could result in personal injury or death.
CAUTION is used to identify unsafe practices which would result in minor personal injury or product and property damage.
NOTE is used to highlight suggestions which will result in enhanced installation, reliability, or operation.

WARNING
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal injury or death. Before installing, modifying, or servicing system, main electrical disconnect switch must be in the OFF position. There may be more than 1 disconnect switch. Lock out and tag switch with a suitable warning label.

WARNING
EXPLOSION HAZARD
Failure to follow this warning could result in death, serious personal injury, death, and/or property damage. Never use air or any gas containing oxygen for leak testing or operating refrigerant compressors. Never allow compressor suction pressure to operate in a vacuum with service valves closed. See Service Manual for pump-down instructions.

Installation Recommendations

NOTE: In some cases noise in the living area has been traced to gas pulsations from improper installation of equipment.

1. This unit is intended to be installed in a location that is 10,000 feet (3000 meters) above sea level or lower.
2. Locate unit away from windows, patios, decks, etc. where unit operation sound may disturb customer.
3. Ensure that vapor and liquid tube diameters are appropriate for unit capacity.
4. Run refrigerant tubes with no bends with centerline bend radius less than 2.5 times the external pipe diameter.
5. Leave some slack between structure and unit to absorb vibration.
6. When passing refrigerant tubes through the wall, seal opening with RTV or other pliable silicon-based caulk. (See Fig. 1.)
7. Avoid direct tubing contact with water pipes, duct work, floor joists, wall studs, floors, and walls.
8. Do not suspend refrigerant tubing from joists and studs with a rigid wire or strap which comes in direct contact with tubing (see Fig. 1).
9. Ensure that tubing insulation is pliable and completely surrounds vapor tube.
10. When necessary, use hanger straps which are 1 in. (25 mm) wide and conform to shape of tubing insulation. (See Fig. 1.)
11. Isolate hanger straps from insulation by using metal sleeves bent to conform to shape of insulation.
12. Provision shall be made for expansion and contraction of long runs of piping.
13. Piping and fittings shall be protected as far as possible against adverse environmental effects. For example, the accumulation of dirt and debris.
14. Piping should be installed to reduce the likelihood of hydraulic shock damaging the system.
15. Certified piping and components must be used in order to protect against corrosion.
16. Flexible pipe elements shall be protected against mechanical damage, excessive stress by torsion, or other forces. They should be checked for mechanical damage annually.
17. Piping material, routing, and installation shall be include protection from physical damage in operation and service, and be in compliance with the national and local codes and standards of the installation site.
18. When setting up refrigerant piping, precautions shall be taken to avoid excessive vibration or pulsation

The outdoor unit contains system refrigerant charge for operation with AHRI rated indoor unit when connected by 15 ft. (4.57 m) of field-supplied or factory accessory tubing. For proper unit operation, check refrigerant charge using charging information  ocated on control box cover and/or in the Check Charge section of this instruction.
IMPORTANT: Maximum liquid-line size is 3/8-in. OD for all residential applications including long line.
IMPORTANT: Always install the factory-supplied liquid-line filter drier. If replacing the filter drier, refer to Product Data Digest for appropriate part number. Obtain replacement filter driers from your distributor or branch.

Installation

CAUTION
CUT HAZARD
Failure to follow this caution may result in personal injury.
Sheet metal parts may have sharp edges or burrs. Use care and wear appropriate protective clothing and gloves when handling parts.
IMPORTANT: All split system and packaged air conditioners must be installed pursuant to applicable regional efficiency standards issued by the Department of Energy. Check Equipment and Job Site
UNPACK UNIT
Move to final location. Remove carton taking care not to damage unit. Inspect Equipment
File claim with shipping company prior to installation if shipment is damaged or incomplete. Locate unit rating plate on unit corner panel. It contains information needed to properly install unit. Check rating plate to be sure unit matches job specifications.
Install on a Solid, Level Mounting Pad If conditions or local codes require the unit be attached to pad, tie down bolts should be used and fastened through knockouts provided in unit base pan. Refer to unit mounting pattern in Fig. 2 to determine base pan
size and knockout hole location. For hurricane tie downs, contact local distributor for details and PE (Professional Engineer) certification, if required by local authorities. On rooftop applications, mount on level platform or frame. Place unit above a load-bearing wall and isolate unit and tubing set from structure. Arrange supporting members to adequately support unit and minimize transmission of vibration to building. Consult local codes governing rooftop applications.
Roof mounted units exposed to winds may require wind baffles. Consult the Application Guideline and Service Manual – Residential Split System Air Conditioners and Heat Pumps for wind baffle construction.
NOTE: Unit must be level to within ±2° (±3/8 in./ft,±9.5 mm/m.) per compressor manufacturer specifications.

Clearance Requirements

When installing, allow sufficient space for airflow clearance, wiring, refrigerant piping, and service. Allow 24 in. (609.6 mm) clearance to service end of unit and 48 in. (1219.2 mm) (above unit. For proper airflow, a 6-in. (152.4 mm) clearance on 1 side of unit and 12-in. (304.8 mm) on all remaining sides must be maintained. Maintain a distance of 24 in. (609.6 mm) between units. Position so water, snow, or ice from roof or eaves cannot fall directly on unit.
On rooftop applications, locate unit at least 6 in. (152.4 mm) above roof surface.
Make Piping Connections

WARNING
PERSONAL INJURY AND ENVIRONMENTAL HAZARD
Failure to follow this warning could result in personal injury or death.
Relieve pressure and recover all refrigerant before system repair or final unit disposal. Use all service ports and open all flow-control devices, including solenoid valves.
Federal regulations require that you do not vent refrigerant to the atmosphere. Recover during system repair or final unit disposal.
CAUTION
UNIT DAMAGE HAZARD
Failure to follow this caution may result in equipment damage or improper operation.
If ANY refrigerant tubing is buried, provide a 6-in (152.4 mm) vertical rise at service valve. Refrigerant tubing lengths up to 36-in (914.4 mm) may be buried without further special consideration. Do not bury lines more than 36-in. (914.4 mm).

UNIT BASE PAN
Dimension in.
(mm)| TIEDOWN KNOCKOUT LOCATIONS in. (mm)
---|---
A| B| C
31-1/2 X 31-1/2
(800 X 800)| 9-1/8 (231.8)| 6-9/16 (166.7)| 24-11/16
(627.1)
35 X 35
(889 X 889)| 9-1/8 (231.8)| 6-9/16 (166.7)| 28-7/16
(722.3)

Fig. 2 – Tiedown Knockout Locations

A05177

Outdoor units may be connected to indoor section using accessory tubing package or field-supplied refrigerant grade tubing of correct size and condition. Rated tubing diameters shown in Table 1 are recommended up to 80 ft. (24.38 m). See Product Data for acceptable alternate vapor diameters and associated capacity losses. For tubing requirements beyond 80 ft. (24.38 m), substantial capacity and performance losses can occur. Following the recommendations in the Longline Guideline will reduce these losses. Refer to Table 1 for field tubing diameters. Refer to Table 2 for accessory requirements. There are no buried-line applications greater than 36-in. (914.4 mm) allowed. If refrigerant tubes or indoor coil are exposed to atmosphere, they must be evacuated to 500 microns to eliminate contamination and moisture in the system.
Outdoor Unit Connected to Factory Approved Indoor Unit
Outdoor unit contains correct system refrigerant charge for operatiowith factory approved AHRI rated indoor unit when connected by 15 (4.57 m) of field-supplied or factory-accessory tubing, and factosupplied filter drier. Check refrigerant charge for maximum efficiency.
Refrigerant Tubing Connection Outdoor
Connect vapor and liquid tubes to fittings on vapor and liquid servivalves (see Table 1.) Use refrigerant grade tubing
Sweat Connection
CAUTION
UNIT DAMAGE HAZARD
Failure to follow this caution may result in equipment damage oimproper operation.
Service valves must be wrapped in a heat-sinking material such as a wecloth while brazing.
WARNING
FIRE HAZARD
Failure to following this warning could result in personal injury, death and/or property damage.
Refrigerant and oil mixture could ignite and burn as it escapes and contacts brazing torch. Make sure the refrigerant charge is properly removed from both the high and low sides of the system before brazing any component or lines.
CAUTION
BURN HAZARD
Failure to follow this Caution may result in personal injury.
Components will be HOT after brazing. Wear appropriate personal protective equipment and allow to cool before handling parts and equipment
Use refrigeration grade tubing. Service valves are closed from factory and ready for brazing. After wrapping service valve with a wet cloth, braze sweat connections using industry accepted methods and materials. Consult local code requirements. Refrigerant tubing and indoor coil are now ready for leak testing. This check should include all field and factory joints
Table 1 – Refrigerant Connections and Recommended Liquid and
Vaport Tube Diameters

UNIT SIZE
(SERIES)| LIQUID| **RATED VAPOR*
---|---|---
Connection
& Max. Tube
Diameter| Connection
Diameter| Tube
Diameter
24| 3/8| 3/4| 3/4
36| 3/8| 7!8| 7/8
48| 3/8| 7/8| 1-1/8
60| 3/8| 7/8| 1-1/8**

• Units are rated with 25 ft. (7.6 m) of lineset. See Product Data sheet for performance data when using different size and length linesets.
  Notes:

  1. Do not apply capillary tube or fixed orifice indoor coils to these units.
  2. For Tubing Set lengths between 80 and 200 ft. (24.38 and 60.96 m) horizontal or 35 ft. (10.7 m) vertical differential 250 ft. (76.2 m) Total Equivalent Length), refer to the Residential Piping and Longline Guideline -Air Conditioners and Heat Pumps using

R-410A refrigerant.
Install Liquid-Line Filter Drier Indoor

CAUTION
UNIT DAMAGE HAZARD
Failure to follow this caution may result in equipment damage or improper operation.

1. Installation of filter drier in liquid line is required.
2. Filter drier must be wrapped in a heat-sinking material such as a wet cloth while brazing.

Refer to Fig. 3 and install filter drier as follows:

1.  Braze 5-in. liquid tube to the indoor coil.
2. Wrap filter drier with damp cloth.
3. Braze filter drier to above 5-in. (127 mm) liquid tube. Flow arrow must point towards indoor coil.
4. Connect and braze liquid refrigerant tube to the filter drier.

Evacuate Refrigerant Tubing and Indoor Coil

CAUTION
UNIT DAMAGE HAZARD
Failure to follow this caution may result in equipment damage or improper operation.
Never use the system compressor as a vacuum pump.
Refrigerant tubes and indoor coil should be evacuated using the recommended deep vacuum method of 500 microns. The alternate triple evacuation method may be used (see triple evacuation procedure in service manual). Always break a vacuum with dry nitrogen.
Deep Vacuum Method
The deep vacuum method requires a vacuum pump capable of pulling a vacuum of 500 microns and a vacuum gage capable of accurately measuring this vacuum depth. The deep vacuum method is the most positive way of assuring a system is free of air and liquid water. A tight dry system will hold a vacuum of 1000 microns after approximately 7 minutes. See Fig. 4.

Mandatory Requirements

Pressure Proof Check

1. Preform a pressure check of the unit with a nitrogen charge of about 200psi.
2.  the Nitrogen holding charge must NOT decrease in pressure for 1 hour, as indicated by the test gauge. The measuring test gauge resolution not exceeding 5% of the holding charge.

Leak Check
This leak check requires a vacuum pump capable of pulling a vacuum of at least 500 microns and a vacuum gage capable of accurately measuring this vacuum depth.

WARNING
FIRE HAZARD
Failure to following this warning could result in personal injury, death and/or property damage.
DO NOT USE FLAMES OR IGNITION SOURCES TO LEAK CHECK.

1. Vacuum unit to 500 microns.
2.  When isolating the unit from the pump, the pressure shall not rise above 1500 microns in 10 minutes.

Final Tubing Check
IMPORTANT: Check to be certain factory tubing on both indoor and outdoor unit has not shifted during shipment. Ensure tubes are not rubbing against each other or any sheet metal or wires. Pay close attention to feeder tubes, making sure wire ties on feeder tubes are secure and tight.

Table 2 – Accessory Usage

Accessory| Required for Low Ambient
Cooling Applications
(Below 55°F / 12.8°C)| **Required for Long Line
Applications*| Required for Sea Coast
Applications
(within 2 miles/3.2 km)**
---|---|---|---
Compressor Start Assist Capacitor and Relay| Yes| Yes| No
Crankcase Heater| Yes (standard on some units)| Yes (standard on some units)| No
Evaporator Freeze Thermostat| Yes| No| No
Hard Shutoff TXV| Yes
(standard w/factory approved
indoor unit)| Yes
(standard w/factory approved
indoor unit)| Yes
(standard w/factory approved
indoor unit)
Liquid Line Solenoid Valve| No| See Residential Piping
and Long Line Guideline| No
Low-Ambient Pressure Switch| Yes| No| No
Support Feet| Recommended| No| Recommended
Winter Start Control| Yes| No| No

• For tubing line sets between 80 and 200 ft. (24.38 and 60.96 m) and/or 35 ft. (10.7 m) vertical differential, refer to Residential Piping and Longline Guideline.

WARNING
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal injury or death.
Do not supply power to unit with compressor terminal box cover removed.

Make Electrical Connections

Be sure field wiring complies with local and national fire, safety, and electrical codes, and voltage to system is within limits shown on unit rating plate. Contact local power company for correction of improper voltage. See unit rating plate for recommended circuit protection device.
NOTE: Operation of unit on improper line voltage constitutes abuse and could affect unit reliability. See unit rating plate. Do not install unit in system where voltage may fluctuate above or below permissible limits.
NOTE: Use copper wire only between disconnect switch and unit.
NOTE: Install branch circuit disconnect of adequate size per NEC to handle unit starting current. Locate disconnect within sight from and readily accessible from unit, per Section 440-14 of NEC.
Route Ground and Power Wires
Remove access panel to gain access to unit wiring. Extend wires from disconnect through power wiring hole provided and into unit control box.
WARNING
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal injury or death. The unit cabinet must have an uninterrupted or unbroken ground to minimize personal injury if an electrical fault should occur. The ground may consist of electrical wire or metal conduit when installed in accordance with existing electrical codes.
Connect Ground and Power Wires
Connect ground wire to ground connection in control box for safety.
Connect power wiring to contactor as shown in Fig. 5.

Connect Control Wiring
Route 24-v control wires through control wiring grommet and connect leads to control wiring (See Fig. 7). Refer to Installation Instructions packaged with thermostat.
Use No. 18 AWG color-coded, insulated (35°C minimum) wire. If thermostat is located more than 100 ft. (30.48 m) from unit, as measured along the control voltage wires, use No. 16 AWG color-coded wire to avoid excessive voltage drop.
All wiring must be NEC Class 2 and must be separated from incoming power leads.
Use furnace transformer, fan coil transformer, or accessory transformer for control power, 24v/40va minimum.
NOTE: Use of available 24v accessories may exceed the minimum 40va power requirement. Determine total transformer loading and increase the transformer capacity or split the load with an accessory transformer as required.
Final Wiring Check
IMPORTANT: Check factory wiring and field wire connections to ensure terminations are secured properly. Check wire routing to ensure wires are not in contact with tubing, sheet metal, etc.
Compressor Crankcase Heater
When equipped with a crankcase heater, furnish power to heater a minimum of 24 hr before starting unit. To furnish power to heater only, set thermostat to OFF and close electrical disconnect to outdoor unit. A crankcase heater is required if refrigerant tubing is longer than 80 ft. (24.38 m). Refer to the Application Guideline and Service Manual Longline Section-Residential Split- System Air Conditioners and Heat Pumps.
Check OAT Thermistor and OCT Thermistor
Attachments
Outdoor Air Temperature (OAT) Thermistor is factory installed by inserting the nibs on either sides of the thermistor body through a keyhole in the bottom shelf of the control box and locking it in place by turning it 90 degrees, such that the spherical end of a nib faces the front of the control box.
Check to make sure the OAT is locked in place. See Fig. 6.

The Outdoor Coil Temperature (OCT) Thermistor is factory installed on the liquid tube between the coil assembly on the copper tube entering the liquid service valve.. See Fig. 7.
Check to make sure the thermistor is securely attached on the copper liquid tube with the clip as shown in Fig. 7.
CAUTION
UNIT DAMAGE HAZARD
Failure to follow this caution may result in unit damage.
Outdoor Coil Temperature (OCT) Thermistor must never be clipped to Aluminum portion of liquid tube. The dissimilar metals cause corrosion potential that may cause a refrigerant leak. Front seating service valves are equipped with Schrader valves.

Airflow Setup with Observer Communicating Furnace or Fan Coil
When using an Observer Communicating Wall Control and communicating indoor equipment, airflow is automatically selected based on equipment size. See Observer Wall Control Installation Instructions and indoor specification sheet for available  djustments.
Airflow Setup with Non-Communicating Furnace or Fan Coil Two−stage compressor operation requires two different indoor airflow settings for proper operation. This outdoor unit is designed for use only with an indoor blower that can be configured for separate low−stage and high−stage airflow (CFM) levels. Refer to Product Specifications Sheets for recommended low−stage and high−stage indoor airflow values.
Refer to indoor unit Installation Instructions to set the indoor blower for the proper low−stage and high−stage airflow values.
NOTE: Optimal comfort, efficiency, and reliability will only be achieved when the indoor airflow is properly set for both low−stage and high−stage operation.

START−UP

CAUTION
UNIT OPERATION AND SAFETY HAZARD
Failure to follow this caution may result in minor personal injury, equipment damage or improper operation.
To prevent compressor damage or personal injury, observe the following:

• Do not overcharge system with refrigerant.
• Do not operate unit in a vacuum or at negative
• pressure.
• Do not disable low pressure switch in scroll compressor
• applications.
• Dome temperatures may be hot.

CAUTION
PERSONAL INJURY HAZARD
Failure to follow this caution may result in personal injury.
Wear safety glasses, protective clothing, and gloves when handling refrigerant and observe the following:
– Front seating service valves are equipped with Schrader valves.
CAUTION
ENVIRONMENTAL HAZARD
Failure to follow this caution may result in environmental damage.
Federal regulations require that you do not vent refrigerant to the atmosphere. Recover during system repair or final unit disposal.
Follow these steps to properly start up the system:

3. After system is evacuated, fully open liquid and vapor service valves.
4. Unit is shipped with valve stem(s) front seated (closed) and caps installed.
Replace stem caps after system is opened to refrigerant flow.
Replace caps finger−tight and tighten with wrench an additional 1/12 turn
5. Close electrical disconnects to energize system.
6. Set room thermostat at desired temperature. Be sure set point is below indoor ambient temperature.
7. Set room thermostat to COOL and fan control to ON or AUTO mode, as desired. Operate unit for 15 minutes. Check system refrigerant charge.

Check Charge
Two-stage equipment should be charged in high stage compressor operation only. Factory charge amount and desired subcooling are shown on unit rating plate. Charging method is shown on information plate inside unit. To properly check or adjust charge, conditions must be favorable for subcooling charging. Favorable conditions exist when the outdoor temperature is between 70°F and 100°F (21°C and 38°C), and the indoor temperature is between 70°F and 80°F (21°C and 27°C). Follow the procedure below: Unit is factory charged for 15ft (4.57 m) of lineset. Adjust charge by adding or removing 0.6 oz/ft of 3/8 liquid line above or below 15ft (4.57 m) respectively. For standard refrigerant line lengths (80 ft/24.38 m or less), allow system to operate in cooling mode at least 15 minutes. When operating with the Observer Wall Control in communicating mode, make sure that indoor airflow is set to the final operating selection (Eff 325, Eff 350, Comfort, Maximum) during charging. If conditions are favorable, check system charge by subcooling method. If any adjustment is necessary, adjust charge slowly and allow system to operate for 15 minutes to stabilize before declaring a properly charged system. If the indoor temperature is above 80°F (27°C), and the outdoor temperature is in the favorable range, adjust system charge by weight based on line length and allow the indoor temperature to drop to 80°F (27°C) before attempting to check system charge by subcooling method as described above. If the indoor temperature is below 70°F (21.11°C), or the outdoor temperature is not in the favorable range, adjust charge for line set length above or below 15ft (4.57 m) only. Charge level should then be appropriate for the system to achieve rated capacity. The charge level could then be checked at another time when the both indoor and outdoor temperatures are in a more favorable range.
NOTE: The Observer Wall Control has a staging timer, to override the staging timer for charging in high-stage create at least a 5 degree difference between room and set point temperatures and hold the “Cool To” button for 10 seconds on the thermostat home screen.
NOTE: If line length is beyond 80 ft (24 m) or greater than 20 ft (6 m) vertical separation, See Long Line Applications Guideline for special charging requirements.
SYSTEM FUNCTIONS AND SEQUENCE OF OPERATION
These models utilize either an Observer Communicating Wall Control or a 2-stage cooling thermostat. With a call for first stage cooling, the outdoor fan and low-stage compressor are energized. If low-stage cannot satisfy cooling demand, high-stage is energized by the second stage of the indoor thermostat. After second stage is satisfied, the unit returns to low-stage operation until first stage is satisfied or until second stage is required again. When both first stage and second stage cooling are satisfied, the compressor will shut off. When a 2-stage unit is operating at low-stage, system vapor (suction) pressure will be higher than a standard single-stage system or high-stage operation. When the outdoor ambient is more than 100°F (38°C), the outdoor fan will continue to run for one minute after compressor shuts off, this reduces pressure differential for easier starting in the next cycle. Communication and Status Function Lights Green communications (COMM) Light (Only with Observer Communicating Wall Control) A green LED (COMM light) on the outdoor board indicates successful communication with the other system products. The green LED will remain OFF until communications is established. Once a valid command is received, the green LED will turn ON continuously. If no
communication is received within 2 minutes, the LED will be turned OFF until the next valid communication.
Amber Status Light (STATUS)
An amber colored STATUS light is used to display the operation mode and fault codes as specified in the troubleshooting section. See Table 5 for codes and definitions.
NOTE: Only one code will be displayed on the outdoor unit control board (the most recent, with the highest priority).
Utility Interface with Non-Communicating Thermostat
The utility curtailment relay should be wired in the Y2 thermostat lead.
This allows a power utility device to interrupt high stage compressor operation during peak load periods. If the utility requires control of low stage compressor operation a second utility curtailment relay should be wired in the Y1 lead.
NOTE: Utility curtailment is not available when operating in communicating mode. To apply utility curtailment with the Observer Wall Control you must use a daughter board kit to convert the control signals to standard thermostat signals.

Compressor Operation
The basic scroll design has been modified with the addition of an internal unloading mechanism that opens a by-pass port in the first compression pocket, effectively reducing the displacement of the scroll. The opening and closing of the by-pass port is controlled by an internal electrically operated solenoid.
The modulated scroll uses a single step of unloading to go from full capacity to approximately 67% capacity. A single speed, high efficiency motor continues to run while the scroll modulates between the two capacity steps.
Modulation is achieved by venting a portion of the gas in the first suction pocket back to the low side of the compressor, thereby reducing the effective displacement of the compressor.
Full capacity is achieved by blocking these vents, thus increasing the displacement to 100%. A DC solenoid in the compressor controlled by a rectified 24 volt AC signal in the external solenoid plug moves the slider ring that covers and uncovers these vents.
The vent covers are arranged in such a manner that the compressor operates at approximately 67% capacity when the solenoid is not energized and 100% capacity when the solenoid is energized. The loading and unloading of the two step scroll is done “on the fly” without shutting off the motor between steps.
NOTE: 67% compressor capacity translates to approximately 75% cooling capacity at the indoor coil. The compressor will always start unloaded and stay unloaded for five seconds even when the thermostat is calling for high- stage capacity.
Crankcase Heater Operation
The crankcase heater is de-energized when the compressor is running. The crankcase heater is energized when the compressor is off and the ambient is less than 42°F. When the ambient temperature is between 65°F and 42°F, the crankcase heater is energized 30 minutes after the compressor is turned off.
When the ambient is above 65°F, the crankcase heater remains de-energized after the compressor is turned off.
Outdoor Fan Motor Operation
The outdoor unit control energizes the outdoor fan any time the compressor is operating. The outdoor fan remains energized if a pressure switch or compressor overload should open. Outdoor fan motor will continue to operate for one minute after the compressor shuts off when the outdoor ambient is greater than or equal to 100°F (38°C) to allow for easier starting during next cooling cycle.
The outdoor fan motor is a PSC type. A fan relay on the control board turns the fan off and on by opening and closing a high voltage circuit to the motor. It does not change speeds between low and high stage operation.

Time Delays
The unit time delays include:

• Five minute time delay to start cooling operation when there is a call from the thermostat or user interface. To bypass this feature hold the “Cool To” or “Heat To” button on the Observer Wall Control for 10 seconds.
• Five minute compressor re-cycle delay on return from a brown-out condition.
•  Two minute time delay to return to standby operation from last valid communication (Observer Communicating Wall Control only).
• One minute time delay of outdoor fan at termination of cooling mode when outdoor ambient is greater than or equal to 100°F (37.8°C).
• There is no delay between staging from low to high and from high to low capacity. The compressor will change from low to high and from high to low capacity “on the fly” to meet the demand.

TROUBLESHOOTING

If the compressor fails to operate with a cooling call, Table 3 can be used to verify if there is any damage to the compressor windings causing system malfunction.

Table 3 – Winding Resistance

Winding| Winding resistance at 70°F +/- 20°F
(21.11°C +/- 11.11°C)
---|---
Unit Size
24| 36| 48| 60
Start
(S-C| 1.652| 1.587| 1.299| 1.203
Run
(R-C)| 1.065| 0.751| 0.477| 0.383

Systems Communication Failure
If communication with the Observer Communicating Wall Control will flash the appropriate fault code. (See Table 5) Check the wiring to the wall control, indoor and outdoor units.
Model Plug
Each control board contains a model plug. The correct model plug must be installed for or the system to operate properly (see Table 4).

Table 4 – Model Plug

The model plug is used to identify the type and size of unit to the control. On new units, the model and serial numbers are input into the board’s memory at the factory. If a model plug is lost or missing at initial installation, the unit will operate according to the information input at the factory and the appropriate error code will flash temporarily. A FAST® Parts replacement board contains no model and serial information. If the factory control board fails, the model plug must be transferred from the original board to the replacement board for the unit to operate.
NOTE: The model plug takes priority over factory model information input at the factory. If the model plug is removed after initial power up, the unit will operate according to the last valid model plug installed, and flash the appropriate fault code temporarily.

Pressure Switch Protection
The outdoor unit is equipped with high and low pressure switches.
If the control senses the opening of a high or low pressure switch, it will respond as follows:

1. De-energize the appropriate compressor contactor.
2. Keep the outdoor fan operating for 15 minutes.
3. Display the appropriate fault code (see Table 5).
4. After a 15 minute delay, if there is still a call for cooling and the LPS or HPS is reset, the appropriate compressor contactor is energized.
5. If LPS or HPS has not closed after a 15 minute delay, the outdoor fan is turned off. If the open switch closes anytime after the 15 minute delay, then resume operation with a call for cooling.
6. If LPS or HPS trips 3 consecutive cycles, the unit operation is locked out for 4 hours.
7. In the event of a high pressure switch trip or high pressure lockout, check the refrigerant charge outdoor fan operation and outdoor coil for airflow restrictions.
8. In the event of a low pressure switch trip or low pressure lockout, check the refrigerant charge and indoor airflow.

Control Fault
If the outdoor unit control board has failed, the control will flash the appropriate fault code. (See Table 5) The control board should be replaced.
Brown Out Protection
If the line voltage is less than 187v for at least 4 seconds, the appropriate compressor contactor and fan relay are de-energized. Compressor and fan operation are not allowed until voltage is a minimum of 190v. The control will flash the appropriate fault code (see Table 5)

230 V Brown Out Protection Defeated:
The brownout feature can be defeated if needed for severe noisy power conditions. This defeat should always be a last resort to solving the problem. Defeat can be initiated through the forced defrost pins as follows:
The brownout toggle is accomplished by shorting the defrost pins from power up with the OAT and OCT sensor connector removed.
After 3 seconds, the status of the force defrost short and the OAT/OCT as open will be checked. If correct, then the brownout will be toggled.

• Status code 6 shows the brownout is disabled.
•  Status code 5 shows the brownout is active.

After the brownout defeat is set, power down and reinstall the OAT/OCT sensor and remove the short from the forced defrost pins. As long as the short on the forced defrost remains, the OAT and OCT faults will not be cleared. The code will continue to be flashed.
The control is shipped with the brownout active. The change in status is remembered until toggled to a new status. A power down/power up sequence will not reset the status. It may be necessary to do the toggle twice to cycle to the desired state of the defeat.

230V Line (Power Disconnect) Detection
If there is no 230v at the compressor contactor(s) when the indoor unit is powered and cooling demand exists, the appropriate error code is displayed (see Table 5). Verify that the disconnect is closed and 230v wiring is connected to the unit.
Compressor Voltage Sensing
The control board input terminals labeled VS and L2 (see Fig. 9) are used to detect compressor voltage status, and alert the user of potential problems. The control continuously monitors the high voltage on the run capacitor of the compressor motor. Voltage should be present any time the compressor contactor is energized, and voltage should not be present when the contactor is de- energized.
Contactor Shorted Detection
If there is compressor voltage sensed when there is no demand for compressor operation, the contactor may be stuck closed or there is a wiring error. The control will flash the appropriate fault code.
Compressor Thermal Cutout
If the control senses the compressor voltage after start-up, and is then absent for 10 consecutive seconds while cooling demand exists, the thermal protector is open. The control de-energizes the compressocontactor for 15 minutes, but continues to operate the outdoor fan.
The control Status LED will flash the appropriate code shown in Table 5After 15 minutes, with a call for low or high stage cooling, the compressor contactor is energized. If the thermal protector has not resetthe outdoor fan is turned off. If the call for cooling continues, the controwill energize the compressor contactor every 15 minutes. If the thermaprotector closes, (at the next 15 minute interval check), the unit wilresume operation. If the thermal cutout trips for three consecutive cyclesthen unit operation is locked out for 4 hours and the appropriate faulcode is displayed.
No 230V at Compressor
If the compressor voltage is not sensed when the compressor should be starting, the appropriate contactor may be stuck open or there is a wiring error. The control will flash the appropriate fault code. Check the contactor and control box wiring.
Troubleshooting units for proper switching between low & high stages 

Check the suction pressures at the service valves. Suction pressure should be reduced by 3-10% when switching from low to high capacity.
NOTE: The liquid pressures are very similar between low and high stage operation so liquid pressure should not be used for troubleshooting.
Compressor current should increase 20-45% when switching from low to high stage. The compressor solenoid, when energized in high stage, should measure 24vac across pin numbers PL5-2 HI and PL5-5 C. When the compressor is operating in low stage the 24v DC compressor solenoid coil is de-energized. When the compressor is operating in high stage, the 24v DC solenoid coil is energized. The solenoid plug harness that is connected to the compressor has an internal rectifier that converts the 24v AC signal to 24v DC.

NOTE: DO NOT INSTALL A PLUG WITHOUT AN INTERNAL
RECTIFIER.
Unloader Test Procedure

The unloader is the compressor internal mechanism, controlled by the DC solenoid, that modulates between high and low stage. If it is suspected that the unloader is not working, the following methods may be used to verify operation.

1. Operate the system and measure compressor amperage. Cycle the unloader on and off at 30 second plus intervals at the Wall Control (from low to high stage and back to low stage). Wait 5 seconds after staging to high before taking a reading. The compressor amperage should go up or down at least 20 percent.
2.  If step one does not give the expected results, remove the solenoid plug from the compressor and, with the unit running and the Wall Control (or Thermostat) calling for high stage, test the voltage output at the plug with a DC voltmeter. The reading should be 24 volts DC.
3. If the correct DC voltage is at the control circuit molded plug, measure the compressor unloader coil resistance. The resistance should be approximately 1640 ohms. If the coil resistance is infinite or is grounded, the compressor must be replaced.

MAJOR COMPONENTS
2-Stage Control

The 2-stage control board controls the following functions:

• Compressor high and low stage operation
•  Outdoor fan motor operation
• Compressor external protection
• Pressure switch monitoring
•  Time delays

Field Connections
On models with non-communicating (Thermostat other than Observer Wall Control) system, the 2-stage control receives 24vac low-voltage control system inputs through the Y1, and Y2 connections located at the bottom of the control board (see Fig. 9). The OD units can be controlled using a standard 2-stage thermostat or Observer Wall Control.
2-Stage Compressor
The 2-stage compressor contains motor windings that provide 2-pole (3500 RPM) operation. Refer to Table 3 for correct winding resistance.
Compressor Internal Relief
The compressor is protected by an internal pressure relief (IPR) which relieves discharge gas into compressor shell when differential between suction and discharge pressures exceeds 550 – 625 psig The compressor is also protected by an internal overload attached to motor windings.
Compressor Control Contactor
The contactor has a 24 volt coil. The electronic control board controls the operation of the appropriate contactor.
TEMPERATURE THERMISTORS
Thermistors are electronic devices which sense temperature. As the temperature increases, the resistance decreases. Thermistors are used to sense outdoor ambient (OAT) and coil temperature (OCT). Refer to Fig. 8 for resistance values versus temperature. If the outdoor ambient or coil thermistor should fail, the control will flash the appropriate fault code (see Table 5.)
IMPORTANT: Outdoor air thermistor and coil thermistor are factory mounted in the final locations. Check to insure thermistors are mounted properly per Fig.6 and Fig.7.
Thermistor Sensor Comparison
The control continuously monitors and compares the outdoor air temperature sensor and outdoor coil temperature sensor to ensure proper operating conditions. The comparison is:
– If the outdoor air sensor indicates 10F (5.56C) warmer than the coil sensor (or) the outdoor air sensor indicates 20F (11.1C) cooler than the coil sensor, the sensors are out of range.
– If the sensors are out of range, the control will flash the appropriate fault code as shown in Table 5.
– The thermistor comparison is not performed during low ambient cooling or defrost operation.
Failed Thermistor Default Operation
Factory defaults have been provided in the event of failure of outdoor air thermistor and/or coil thermistor. If the OAT sensor should fail, low ambient cooling will not be allowed and the one minute outdoor fan-off delay will not occur. If the OCT sensor should fail, low ambient cooling will not be allowed.
OAT Thermistor must be locked in place with spherical nib end facing towards the front of the control box.

Table 5 – Status Codes

OPERATION| FAULT| AMBER LED
FLASH CODE| Possble Cause and Action
---|---|---|---
Standby **– no            call       for ****unit**

operation

| None| On sold, no lash| Normal operation
Low StageCootaleat Operation| None| 1, pause| Normal operatic.,
High Stage Cool/fiat Operation| None| 2. Pause| Normal operation
Brown out protection is Disabled| None| 5. pause| User mode selection. see instructions for more deist
Brown out protection is Active| None| 8, Pause| User mode selection, see instructions br more detai
| System Communications Failure| 18| Communicaton with Observer Wal Control lost. Check wiring b Observer Wall Contd, indoor and outdoor urits
| Invalid Model Plug| 25| Control does not detect a model plug a detects and invalid mods plug. Urit wl not operate without correct model plug.
| High Pressure Switch Open| 31•| Ngh pressure switch trip. Check refrigerant charge, outdoor fan operalon and cots for airflow restrictions.
| Low Pressure Switch a Discharge Tarp

Switch Open

| 32| Low pressure switch a discharge temperature switch trip. Check refrigerant charge and indoor Be tow
| Control Fault| 45| Outdoor wit control board has failed. Cenci board needs to be replaced.
| Brown Out (230 v)| 48| Line Voltage <187V for at least 4 seconds. Compressor and fan Megaton not slowed until voltage > 190v. Verify tie voltage.
| No 230val Urit| 47| There is not 230v at the contactor when indoor unit is powered and coolingMealng demand exists. Verify tie discomect is dosed and 230v wiring is corrected to the unit.
| Outdoor At Terry Sensa law| 53| Outdoor Er sensa not reading or out of range. Ohm out sensor and died( wing
| Outdoor Coil Sensor Fall| 55| Ca senses not reacting a out of range. Ohm out sensor and check wiring
| Themistoroout of range| 58| Improper relationdM between cod sensor and outdoor air sensor. Ohm out sensors aid check wing.
| Low Stage Thermal Cutout| 71| Compressor operaton detected then disappears Mite low stage demand exists. Possible causes are Internal compressor overload tip a start relay and capacitor held Si crock too big (if instated)
| High Stage Thermal Cutout| 72′| Compressor operation detected then disappears Mite high stage
demand exists. Possible causes are internal compressor overload
tip a start relay and capacitor held b circuit too big (if instated)
| Contactor Shorted| 73| Compressor voltage sensed when no demand for compressor operation exists. Contactor may be skid( dosed a there is a Mks “Mt
| No 230V at Compresses| 74| Compressor voltage not sensed when compressor should be starling. Disconnect may be open or contactor may be stuck open or tiers is a wiring error.
| Low Stage Thermal Lockout| 82| Thermal cubut occurs Si twee consecutive lowThigh cycles. Low Sage locked at for 4 hours or until 24v parser recycled.
| High Stage Thermal Lockout| 82| Thermal tubatuba OCCUS in three consecutive Iow,bigh cycles. Sigh Sage locked out for 4 hours or until 24v power recycled.
| Low Pressure Lockout| 83| Low pressure switch trip has occurred diving 3 consecuthe aides. Unit operaton locked out for 4 limn or until 24v power recycled.
| High Pressure Lockout| 84| High pressure switch trip has marred during 3 commutes cyan. Unit operation locked out for 4 hours or mt. 24v power recycled.
*Sequence: Compressor contactor is de-energized and outdoor fan is energized for up to 15 minutes. If donand still exists, control will energize compressor.

Final Checks
IMPORTANT: Before leaving job, be sure to do the following:

1. Ensure that all wiring is routed away from tubing and sheet metal edges to prevent rub– through or wire pinching.
2. Ensure that all wiring and tubing is secure in unit before adding panels and covers. Securely fasten all panels and covers.
3.  Tighten service valve stem caps to 1/12–turn past finger tight.
4. Leave Owner’s Manual with owner. Explain system operation and periodic maintenance requirements outlined in manual.

CARE AND MAINTENANCE

For continuing high performance and to maintain warranty coverage, periodic maintenance must be performed on this equipment.
Frequency of maintenance may vary depending upon geographic areas, such as coastal applications. See Owner’s Manual for information.

Use of the AHRI Certified TM Mark indicates a manufacturer’s participation in the program For verification of certification for individual products, go to www.ahridirectory.org

© 2022 Carrier. All rights reserved.
A Carrier Company
Edition Date: 11/22
Catalog No: CHT4A7T-01SI
Replaces:New
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.

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