EMERSON 21M51U-843 Universal Integrated Furnace Control Kit Instructions
- August 27, 2024
- Emerson
Table of Contents
EMERSON 21M51U-843 Universal Integrated Furnace Control Kit
Product Information
Product Name: Universal Integrated Two-Stage 120V Hot Surface Ignition
Control Kit
Model Number: 21M51U-843
Description: Aftermarket universal replacement control kit for two-stage
furnace products with PSC blower and inducer motors.
Compatibility: Replaces Goodman/Amana, Lennox/Armstong, Trane/American
Standard, and York applications.
Specifications
- Electrical Ratings: Input Voltage: 120 VAC, 60 Hz (Class II transformer required)
- Max. Input Current @ 24 VAC: 800mA
Installation Instructions
Mounting and Wiring
- Disconnect electrical power and gas supply to the unit, then remove the unit access panel.
- Mark and disconnect all wires from the existing control and remove the old control.
- Mount the new control board in the unit and reconnect all wires.
- Verify and set Stage Delay, Heat Off Delay, Trial for Ignition, Heat On Delay, and Cool Off Delay settings according to prior board configuration or instructions.
- If replacing a 50A51 control, set Trial for Ignition to 7 seconds.
- Secure wiring with provided cable ties if necessary.
- Reinstall unit access panels and reconnect electric power and gas supply.
- Verify unit operation by placing the thermostat in heating mode and initiating a call for heat.
FAQ
Q: Is this control kit compatible with all two-stage furnace products?
A: The 21M51U-843 is designed as a universal replacement for two-stage furnace
products with PSC blower and inducer motors. It replaces specific brands like
Goodman/Amana, Lennox/Armstong, Trane/American Standard, and York
applications.
21M51U-843
Universal Integrated Two-Stage
120V Hot Surface Ignition Control Kit
INSTALLATION INSTRUCTIONS
FAILURE TO READ AND FOLLOW ALL INSTRUCTIONS CAREFULLY BEFORE INSTALLING OR OPERATING THIS CONTROL COULD CAUSE PERSONAL INJURY AND/OR PROPERTY DAMAGE.
DESCRIPTION
The 21M51U-843 is an aftermarket universal replacement control kit for two-
stage furnace products with PSC blower and inducer motors.
This control replaces Goodman/Amana, Lennox/Armstong, Trane/American Standard,
and York applications.
TWINNING: 21M51U-843 can be twinned. Both control boards must be from the same
manufacturer for proper functionality.
Parts included
- 50M51-843 Integrated Furnace Control
- 21D64-2 HotRod Universal Ignitor Kit (120V)
- Trane Ignitor Mounting Bracket
- 3 – Mounting Screws
- 5 – Motor Lead Extensions
- Installation Instructions
ELECTRICAL RATINGS
Input Voltage: 120 VAC, 60 Hz (Class II transformer required) Max. Input
Current @ 24 VAC: 800mA + MV
Relay & Triac Load Ratings:
- Gas Valve Relays: 1.5 amps @ 24 VAC, 60 Hz
- Ignitor: 4.0 amps @ 132 VAC, 60 Hz
- Inducer Relays: 2.2 FLA – 3.5 LRA @ 120 VAC
- Circulator Relays: 14.5 FLA – 25.0 LRA @ 120 VAC
- Humidifier Load: 1.0 A max @ 120 VAC
- Electronic Air Cleaner Load: 1.0 A max @ 120 VAC
Flame Current Requirements:
- Minimum current to ensure flame detection: 0.3 μA DC*
- *Measured with a DC microammeter in series with flame probe lead
- Operating Temperature Range: -40° to 175°F (-40 to 80°C)
H midity Range
- 5% to 93% relative humidity (non-condensing)
Gases Approved
Natural, Manufactured, Mixed, Liquid Petroleum, and LP Gas Air Mixtures are
all approved for use.
SPECIFICATIONS
CAUTION
- Risk of Electric Shock. Disconnect electric power to system until installation is complete.
- Do not use on circuit exceeding specified voltage. Higher voltage will damage control and could cause shock or fire hazard.
- This control is not intended for use in locations where it may come in contact with water.
- May cause flame rollout. Shut off main gas to heat-ing system until installa-tion is complete.
INSTALLATION
MOUNTING AND WIRING
Refer to Typical System Wiring Diagram on page 3 NOTE: All wiring should be
installed according to local and national electrical codes and ordinances.
- Disconnect electrical power and gas supply to unit, then remove unit access panel.
- Mark and disconnect all wires from the existing control, then remove the old control.
- Mount and new control board in the unit and reconnect all the wires.
- Verify Stage Delay, Heat Off Delay, Trial for Ignition, Heat On Delay, and Cool Off Delay settings by matching prior boards configuration or refer to Dipswitch Configuration section of instructions and original OEM install manual and wiring diagrams.
- If replacing 50A51 control, set Trial for Ignition for 7 seconds.
- Secure any wiring with the provided cable ties as necessary.
- Reinstall unit access panels and reconnect electric power and gas supply to the unit.
- Verify unit operation by placing thermostat in heating mode and initiating a call for heat by adjusting thermostat 5 degrees above room temperature.
NOTES
- Motor lead extensions are included to be used if the original wiring does not reach the control after mounting.
- Lennox applications will require connection to the stand alone flame probe terminal.
- The installer may have to modify existing ignitor hole to accommodate the larger 21D64-2 (ceramic diameter 0.394″)
- When replacing Amana 50A51-225, Amana 50A51-235, and York 50A51-243, “CIRC INPUT” is a redundant line voltage connection which should be taped and tied off.
DIPSWITCH CONFIGURATION
NOTES
- Cycle power after changes are made.
- For best results, set dip switches to prior boards configuration or refer to original OEM install manual for further details.
- Only use Stage W2 delay with single-stage thermostat.
- AUTO mode is based on an algorithm method of energizing the second stage gas valve based on the recent average of the heating duty cycle.
WIRING DIAGRAM
OPERATION
HEAT MODE
COOL MODE
FAN MODE
****TROUBLESHOOTING
Green LED
Flash
| Amber LED
Flash
| Red LED
Flash
| Error/Condition| Comments/Troubleshooting
---|---|---|---|---
| | 1| Flame sensed when no flame should be present| Verify the gas valve is
operating and shutting down properly. Flame in burner assemble should
extinguish promptly at the end of the cycle. Check orifices and gas pressure.
| | 2| Pressure switch stuck closed/ inducer error| Pressure switch stuck
closed. Check switch function, verify inducer is turning off.
| | 3| 1st-stage pressure switch stuck open/inducer error| Check pressure
switch function and tubing. Verify inducer is turning on the pulling
sufficient vacuum to engage switch.
| | 4| Open limit switch| Verify continuity through rollout switch circuit.
| | 5| Open rollout/open fuse detect| Verify continuity through rollout switch
circuit, check fuse.
| | 6| 1st-stage pressure switch cycle lockout| If the first stage pressure
switch cycles 5 times (open, closed) during one call for heat from the
thermostat the control will lockout. Check pressure switch for fluttering,
inconsistent closure or poor vacuum pressure.
| | 7| External lockout (retries)| Failure to sense flame is often caused by
carbon deposits on the flame sensor, a disconnected or shorted flame sensor
lead or a poorly grounded furnace. Carbon deposits can be cleaned with emery
cloth. Verify sensor is not contacting the burner and is located in a good
position to sense flame. Check sensor lead for shorting and verify furnace is
grounded properly.
| | 8| External lockout (ignition recycles exceeded where flame is established
and then lost)| Check items for exceeded retries listed above and verify valve
is not dropping out allowing flame to be established and then lost.
| | 9| Grounding or Reversed polarity| Verify the control and furnace are
properly grounded. Check and reverse polarity (primary) if incorrect.
| | 10| Control valve contacts energized with no call for heat| Verify valve
is not receiving voltage from a short. If a valve wiring is correct and
condition persists, replace control.
| | 11| Limit switch open – possible blower failure overheating limit|
Possible blower failure, restricted air flow through appliance or duct work.
Verify continuity through limit switch circuit and correct overheating cause.
| | 12| Ignitor contact failure| Fault code indicates the control ignitor
contacts are not functioning properly. Replace control.
| | Solid| Internal fault condition| Control contacts for gas valve not
operating or processor fault. Reset control. If condition persists replace
control.
Green LED
Flash
| Amber LED
Flash
| Red LED
Flash
| Error/Condition| Comments/Troubleshooting
---|---|---|---|---
| | Rapid| Twinning error| Check wire connections. If condition persists,
replace control.
| | 3
Double
| 2nd-stage Pressure Switch Stuck Open/Inducer Error| Check pressure switch
function and tubing. Verify inducer is turning on and pulling sufficient
vacuum to engage switch.
| 1| | Normal Operation with call for first stage heat| Normal operation –
first stage
| 2| | Normal Operation with call for second stage heat| Normal operation –
second stage
| 3| | W2 present with no W1| Second stage call for heat on thermostat circuit
with no call for first stage. Verify dip switches are set for two stage
thermostat and check thermostat first stage circuit. Configured for a multi-
stage thermostat the control will not initiate heating unless first stage call
from thermostat is received.
| 4| | Y present with no G call| Control will allow cooling to operate with
only a “Y” signal from the thermostat but will also trigger this code. Verify
thermostat is energizing both “Y” and “G” on call for cool. Check “G” terminal
connections.
| Rapid| | Low flame sense current| Low flame sense current is often caused by
carbon deposits on the flame sensor, a poorly grounded furnace or a mis-
aligned flame sense probe. Carbon deposits can be cleaned with emery cloth.
Check for improve furnace and module ground. Verify sensor is located in or
very near flame as specified by the appliance manufacturer.
1| | | Call for cool| Normal operation.
Solid| | | Standby| Waiting for call from thermostat or receiving thermostat
call for cool.
SYSTEM LOCKOUT AND DIAGNOSTIC FEATURES
FAULT RECALL
When the control is in standby mode (no call for heat or cool), press the
“LAST ERROR” button for approximately one – five seconds. The LED will flash
up to five stored fault codes, begin-ning with the most recent. If there are
no fault codes in memory, the LED will flash two green flashes.
FAULT CODE RESET
When the control is in standby mode (no call for heat or cool), press the
“LAST ERROR” button for five to ten seconds or until the diagnostic LED begins
to rapid flash. The LED will flash three green flashes when the memory has
been cleared.
CONTROL RESET
- interrupt the call for heat at the thermostat for at least one second but less than 20 seconds (if flame is sensed with the gas valve de-energized, interrupting the call for heat at the thermostat will not reset the control).
- Interrupt the 24 VAC power at the control for at least 20 seconds. You may also need to reset the flame rollout sensor switch.
- After 1 hour in lockout, the control will automatically reset itself.
Emerson and White-Rodgers are trademarks of Emerson Electric Co. ©2017 Emerson Electric Co. All rights reserved.
References
Read User Manual Online (PDF format)
Read User Manual Online (PDF format) >>