The Home Depot CNT08576 Integrated Furnace Control for Furnaces with Variable Fan Speed Installation Guide

The Home Depot CNT08576 Integrated Furnace Control for Furnaces with

Variable Fan Speed

Operator: Save these instructions for future use!

FAILURE TO READ AND FOLLOW ALL INSTRUCTIONS CAREFULLY BEFORE INSTALLING OR OPERATING THIS CONTROL COULD CAUSE PERSONAL INJURY AND/OR PROPERTY DAMAGE.

DESCRIPTION

• The CNT08576 is a two-stage automatic gas interrupted ignition control employing a microprocessor to continually monitor, analyze, and control the proper operation of the gas burner and inducer, and provide signal for proper operation of variable fan speed timing.
• Signals interpreted during continual surveillance of the two-stage thermostat and flame sensing element initiate automatic ignition of the burner, sensing of the flame, and system shutoff during normal operation.
• The control incorporates system fault analysis for quick gas flow shutoff, coupled with automatic ignition retry upon sensing a fault correction.

PRECAUTIONS

GENERAL PRECAUTION

• Application of this type of control may cause flame rollout on initial startup and could cause personal injury and/or property damage.
• Replace only with exact model number, including dash number. Failure to use exact replacement control could cause personal injury and/or property damage.

NOTE

• For 24 VAC applications, this control must be programmed by the field technician. Follow the steps outlined in the Model Number Recovery section.
• If in doubt about whether your wiring is millivolt, line, or low voltage, have it inspected by a qualified heating and air conditioning contractor or licensed electrician.
• Do not exceed the specification ratings.
• All wiring must conform to local and national electrical codes and ordinances.
• This control is a precision instrument, and should be handled carefully. Rough handling or distorting components could cause the control to malfunction.

CAUTION

• To prevent electrical shock and/or equipment damage, disconnect electric power to system at main fuse or circuit breaker box until installation is complete.
• This control is not intended for use in locations where it may come in direct contact with water. Suitable protection must be provided to shield the control from exposure to water (dripping, spraying, rain, etc.).
• Label all wires prior to disconnection when servicing controls. Wiring errors can cause improper and dangerous operation.
• Following installation or replacement, follow appliance manufacturers’ recommended installation/service instructions to insure proper operation.
• Do not use on circuits exceeding specified voltage. Higher voltage will damage control and could cause shock or fire hazard.

WARNING

• Do not short out terminals on gas valve or primary control to test. Short or incorrect wiring will damage thermostat and could cause personal injury and/or property damage.

MODEL NUMBER RECOVERY

Programming a Replacement

Programming a Replacement CNT08576

Replacement controls are not programmed with model number attributes and MUST be programmed by the technician. The furnace control will not operate until the programming is successfully completed. There are two methods of programming for 24V applied furnaces. This process is called MNR, or Model Number Recovery

Using the Diagnostic App

1. Install the replacement control with all wire harness connections made.
2. Field wiring should be done after the programming is complete.
3. With power applied, wait for the Seven Segment display reads i dL (Idle).
4. Momentarily push the BLE button and release. The Status and Comm LED’s will begin to flash ON and OFF at the same time.
5. Connect the Diagnostics app to the furnace. The furnace will show up on the app with no model and no serial number.
6. Follow the prompts and select the corresponding model number of the furnace.

Using the Menu / Option Buttons

1. Install the replacement control with all wire harness connections made.
2. Field wiring should be done after the programming is complete.
3. With power applied, push and hold the BLE button for at least 10 seconds, but not more than 15 seconds.
4. Wait for the Seven Segment display to start flashing . This may take ~35-40 seconds.
5. Press and release the Menu button and stops flashing
6. Press the Option button to scroll to the number that corresponds to the model number of the furnace in the table above.
7. Push the Menu button 2 times to save the programming.
8. MNR and the number will flash 3 times to confirm programming

NOTE: If a mistake is made in the programming, repeat steps 3-8.

SPECIFICATIONS

• Max. Input Current @ 24 VAC: 550mA + MV
• Relay Load Ratings:
  • Gas Valve Relay: 1.5 A @ 24 VAC, 60 Hz, 0.6 pf
  • Ignitor: 2.0 A @ 120 VAC
  • Humidifier Relay: 1.0 A @ 120 VAC, 60 Hz.
  • Electronic Air Cleaner Relay: 1.0 A @ 120 VAC, 60 Hz
• Flame Current Requirements:
  • Minimum current to insure flame detection: 1 MA DC*
  • Maximum current for non-detection: 0.1 HA DC*
  • Maximum allowable leakage resistance: 100 M ohms
• *Measured with a DC microammeter in the flame probe lead
• OPERATING TEMPERATURE RANGE:
  • -40° to 175°F (-40° to 80°C)
• HUMIDITY RANGE:
  • 5% to 95% relative humidity (non-condensing)
• Timing Specs: (@ 60 Hz**) / maximum
  • Flame Establishing Time: 0.8 sec
  • Flame Failure Response Time: 2.5 sec
• Gases Approved: Natural, Manufactured, Mixed, Liquid Petroleum, and LP Gas Air Mixtures are all approved for use.

TIMING SPECIFICATIONS

(All times are in seconds, unless noted otherwise)
CNT08576

*These times will vary depending on option

INSTALLATION

MOUNTING AND WIRING

WARNING

• Do not use on circuits exceeding specified voltage. Higher voltage will damage control and could cause shock or fire hazard.

CAUTION

• To prevent electrical shock and/or equipment damage, disconnect electric power to system at main fuse or circuit breaker box until installation is complete. Failure to earth ground the appliance or reversing the neutral and hot wire connection to the line can cause shock hazard.
• Shut off main gas to heating system until installation is complete.
• Route and secure all wiring as far from flame as practical to prevent fire and/or equipment damage.
• Replace CNT08576 control as a unit – no user serviceable parts.

NOTE

• All wiring should be installed according to local and national electrical codes and ordinances.
• The CNT08576 control may be mounted on any convenient surface using the 9 standoffs provided.
• The control must be secured to an area that will experience a minimum of vibration and remain below the maximum ambient temperature rating of 175°F. The control is approved for minimum ambient temperatures of -40°F. Any orientation is acceptable.
• Refer to the wiring diagram and wiring table when connecting the CNT08576 control to other components of the system.
• UL approved, 105°C rated 18 gauge min., stranded, 2/64″ thick insulation wire is recommended for all low voltage safety circuit connections. Refer to CNT08576 control specification sheet for recommended terminals to mate with those on the control.
• UL approved, 105°C rated 16 gauge min., stranded, 4/64″ thick insulation wire is recommended for all line voltage connections.
• Refer to CNT08576 control specification sheet for recommended terminals to mate with those on the control.
• Following installation or replacement, follow appliance manufacturer’s recommended installation or service instructions to insure proper operation.

TYPICAL SYSTEM WIRING TABLE

• Spade terminals are 0.25″ x 0.032″
  ** Maximum recommended flame probe wire length is 36 inches.

TYPICAL SYSTEM WIRING DIAGRAM

OPERATION

24V Mode

LED TIMINGS

Comm Mode

The three 7-segment display, DS1, indicates the operating status of the control. It also shows options setup information and error codes.

STATUS MENU

In normal operation, the display will show status of the control as indicated in below.

*Blower flow (CFM) – Blower CFM will be displayed in the status menu as ArF, following with three digit numbers. To get the blower CFM, the three digit should be multiplied by 10.
Example: 800 CFM will be displayed as 080, 1360 CFM as 136, less than 100 CFM as A00.

• On a call for heat or cool, the display will continually alternate to indicate the mode and blower flow. If a fault occurs, the fault code will be additionally shown.
• Example: Call for cool stage 1 with blower CFM of 1300 – display will repeatedly show CL 1 ArF 130
• Call for heat second stage with blower CFM of 1100 with open limit switch fault – display will repeatedly show HPE ArF 110 Е04
• The open limit switch error will only appear with an active call.

SETTING UP YOUR SYSTEM

• To change any factory default value, first remove any CALL from the furnace and allow fan off delays to finish. (IDL should be seen on the display.)
• Scroll to the selected Menu item by momentarily depressing the MENU key and then depress the OPTION key to the desired setting. Then momentarily depress the “MENU” key again to save the change.

OPTIONAL SETUP MENU

With Power applied to the control and no active calls, the optional setup menu can be accessed to select options available on the control. Momentarily press the MENU switch (SW2) to begin the Menu and to navigate through menu items. To change the options available for a particular menu item, press the OPTION switch (SW1). While navigating in the option menu, the currently displayed option if applicable can be selected by pressing the main switch and then the display goes back to the main menu if currently is in.”To exit the menu either wait the 30s time out period, or scroll through the menu to the idle state.”

See below table menu items sequence and available setup options:

• Do not adjust COF above 75%
  **CFM/Ton selections range from 290-450

Important

• When applied with zoning or a VSPD outdoor unit, the CFM/Ton must be set to 400

HEAT MODE

In a typical system, a call for first stage heat is initiated by closing the W1 thermostat contacts. The Humidifier relay is closed and the inducer blower is enabled at low speed. The control waits for the stage 1 pressure switch to close. When the pressure switch closes the silicon nitride ignitor is powered. On a call for gas heat, or transition to a given gas heat stage, the inducer is commanded to a speed in order to close the pressure switch for that stage.

120V Silicon Nitride Ignitor manufactured by Kyocera must be used. At the end of the ignitor warm-up time, the first stage of the two-stage manifold gas valve is energized (low fire). Flame must be detected within 5 seconds. If flame is detected, the delay-to- fan-on period begins. After the delay-to-fan- on period ends, the circulator is enabled and air cleaner relay is closed.

A call for second stage heat (W1 and W2) after a call for first stage heat will activate a 2nd stage delay. Following the delay, the inducer motor is driven at high speed. The control checks the 2nd stage pressure switch. When the pressure switch closes, the 2nd stage gas valve turns on and the circulator is enabled at high speed.

When the second stage of the thermostat is satisfied, the inducer motor is reduced to low speed, and the 2nd stage gas valve and high circulator speed are de-energized. When the first stage of the thermostat is satisfied, the gas valve is de-energized and the heat delay-to-fan-off timing begins. The inducer will post purge for an additional 5 seconds. When this time is expired, the inducer and humidifier will de-energize. Upon completion of the heat delay-to- fan-off period, the circulator and air cleaner are de-energized.

If flame is not detected during the trial-for-ignition period, the gas valve is de-energized, the ignitor is turned off, and the control goes into the “retry” sequence. “No error is generated.” The “retry” sequence starts with a 60-second interpurge, enabling the inducer at low speed for 60 seconds following an unsuccessful ignition attempt (flame not detected). After this wait, the ignition sequence is restarted. If this ignition attempt is unsuccessful, 9 more retries will be made before the control goes into a system lockout for one hour.

If flame is detected, then lost, the control will repeat the initial ignition sequence for a total of ten “recycles”. After ten unsuccessful attempts to sustain flame, the control will go into a system lockout for one hour.
During burner operation, a momentary loss of power will de-energize the main gas valve. When power is restored, the gas valve will remain de-energized and a restart of the ignition sequence will begin immediately.

A momentary loss of gas supply, flame blowout, or a shorted or open condition in the flame probe circuit will be sensed within 2 seconds. The gas valve will de-energize and the control will restart the ignition sequence. Recycles will begin and the burner will operate normally if the gas supply returns, or the fault condition is corrected, before the last ignition attempt. Otherwise, the control will go into system lockout. If the control has gone into system lockout, it may be possible to reset the control by a momentary power interruption of five seconds or longer. Refer to PRECAUTIONARY, SYSTEM LOCKOUT, AND DIAGNOSTIC FEATURES.

COOL MODE

In a typical system, a call for cool is initiated by closing the thermostat contacts. This energizes the compressor, circulator output and air cleaner. After the thermostat is satisfied, the compressor is de-energized and the optional cool mode delay- to-fan-off period begins. After the optional delay- to-fan-off period ends, the circulator and air cleaner are de-energized.

MANUAL FAN ON MODE

• If the thermostat fan switch is moved to the ON position, the circulator and air cleaner are energized.
• When the fan switch is returned to the AUTO position, the circulator and air cleaner are de-energized.

PRECAUTIONARY, SYSTEM LOCKOUT, AND DIAGNOSTIC FEATURES

PRECAUTIONARY FEATURES

The following precautionary features are built into the control.

1. If the high temperature limit or flame rollout sensor open at any time, the gas valve is de-energized.
2. During a call for heat cycle, if flame is sensed at any time when the gas valve is de-energized, the circulation “E” output and inducer fan are energized at low speed in conjunction with system lockout.
3. If the high limit (and/or auxiliary limit) switches) open at any time during a call for heat, the circulator blower and inducer fan are energized at low speed.

SYSTEM LOCKOUT FEATURES

When system lockout occurs, the gas valve is de-energized, the circulator “E” output and the inducer blower are energized at low speed. The diagnostic indicator menu will flash to indicate system status. (System lockout will never override the precautionary features described above.)

To reset the control after system lockout, do one of the following:

1. Interrupt the call for heat at the thermostat for at least one second and less than twenty seconds (if flame is sensed with the gas valve de-energized, interrupting the call for heat at the thermostat will not reset the control).
2. Interrupt the 24 VAC power at the control for at least five seconds. You may also need to reset the flame rollout sensor switch.
3. After one hour in lockout, the control will automatically reset itself.

DIAGNOSTIC FEATURES

The control continuously monitors its own operation and the operation of the system. If a failure occurs the control can indicate the active error as well as the last 6 faults on the three 7-segment display.
To view the active Error, press the MENU switch, then press OPTION switch. To view the Last 6 faults, press the MENU switch again and press the OPTION switch to step through the previous alarms (most recent to oldest).

When the alarm(s) is active, the alarm(s) will be saved into Last 6 Faults Menu. The alarms) will be stored in the sequence they occur. If the total number of alarms occurred is more than max alarms that can be stored, the oldest alarm will be pushed out from the Active Error Menu first. The alarm(s) will be displayed as follows:

RUN TEST MODE

To enter Run Test Mode, scroll to run using the MENU switch, then push the OPTION switch. The LED will flash run three times, then begin the test. To exit the test mode, momentarily push the MENU switch, cycle power to the furnace, or make a valid thermostat call for capacity or fan.

Sequence of Run Test Mode:

The above sequence will repeat two more times unless the Run Test Mode is exited, see above.

Important

• The Run Test Mode does not test fire the furnace or bring the outdoor unit on. It is designed to allow the technician to observe each mode to ensure the IFC, inducer, and circulating blower are performing as intended.

CLEAR ALL ALARMS

To clear the stored faults, scroll to the last 6 faults menu (L6F), enter the menu by scrolling to the right and hold the OPTION switch for at least 5 seconds. Release and a set of 3 dashes will be seen 3 times. This confirms the faults have been cleared.

ALARM PRIORITY & CODE DEFINITION

RESET TO FACTORY DEFAULTS

The control can be Reset to Factory Default function in any operation/idle state. The operating parameters will be reset to factory default and the last 6 errors will be cleared. The factory default parameters shall not take effect until next valid call or next blower/inducer operation. The reset will not clear an active alarm.
To reset the control, press and hold both the MENU and OPTION switches for more than 5 seconds and less than 30 seconds. All options will reset to the factory default value and clear the Last 6 Faults. The three display segments will flash “F” and “d”three times to indicate the process is finished successfully, and then go back to the Status Menu.

Factory reset can be performed at any time except:

• When PM verification is in progress during the power-up sequence.
• When Fault erase is requested from the last 6 faults menu and the fault erase is in progress.

FAQ

Frequently Asked Questions

• Q: What should I do if the product does not power on?
  • A: Check the power source and cable connections. If the issue persists, contact customer support for assistance.
• Q: How often should I clean the product?
  • A: It is recommended to clean the product regularly, at least once a month, to ensure proper functioning.
• Q: Can I use the product outdoors?
  • A: Refer to the user manual to determine if the product is suitable for outdoor use. Avoid exposing the product to extreme weather conditions.

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