If you're looking for help fixing your McQuay Furnace, look no further! Our comprehensive McQuay Furnace error code guide will explain common issues, provide tips, and show you how to read your model's error codes.

CODE: SLOW GREEN FLASH 
RESULT: Normal operation 

CODE: SLOW AMBER FLASH 
RESULT: Normal operation with call for heat 

CODE: RAPID RED FLASH 
RESULT: Twinning error, incorrect 24V phasing. 
FIX: Check twinning wiring. Flame sense current is below 1.5 microamps 

CODE: RAPID AMBER FLASH 
RESULT: Check and clean flame sensor. Check for proper gas flow. Verify that current is greater than 1.5 microamps at flame current test pad. 

CODE: 4 AMBER FLASHES 
RESULT: The control is receiving a "Y" signal from the thermostat without a "G" signal, indicating improper thermostat wiring. 

CODE: 1 RED FLASH 
RESULT: This indicates that flame was sensed when there was not a call for heat. 
FIX: The control will turn on both the inducer motor and supply air blower. A gas valve that leaks or is slow closing would typically cause this fault. 

CODE: 2 RED FLASHES 
RESULT: This indicates that the normally open pressure switch contacts are stuck in the closed position. 
FIX: The control confirms these contacts are open at the beginning of each heat cycle. This would indicate a faulty pressure switch or miswiring. This indicates the normally open pressure switch contact did not close after the inducer was energized. 

CODE: 3 RED FLASHES 
RESULT: This could be caused by a number of problems: faulty inducer, blocked vent pipe broken pressure switch hose or faulty pressure switch. 

CODE: 4 RED FLASHES 
RESULT: This indicates that the main limit switch has opened its normally closed contacts. 
FIX: The control will operate the supply air blower and inducer. This condition may be caused by: dirty filter, improperly sized duct system, incorrect blower speed setting, incorrect firing rate or faulty blower motor. Also, this fault code could be caused by a blown fuse located on the control board. 

CODE: 5 RED FLASHES 
RESULT: This fault is indicated if the normally closed contacts in the rollout switch opens. 
FIX: The rollout control is manually reset. If it has opened, check for proper combustion air, proper inducer operation, and primary heat exchanger failure or burner problem. Be sure to reset the switch and cycle power (24 VAC) to the control after correcting the failure condition. Also, this fault code could be caused by a blown fuse located on the control board. 

CODE: 6 RED FLASHES 
RESULT: This indicates that after the unit was operating, the pressure switch opened 4 times during the call for heat. 
FIX: If the main blower is in a "Delay on" mode, it will complete it, and any subsequent delay off period. The furnace will lock out for one hour and then restart. 

CODE: 7 RED FLASHES 
RESULT: This fault code indicates that the flame could not be established. This no-light condition occurred 3 times (2 retries) during the call for heat before locking out. 
FIX: Low gas pressure, faulty gas valve, dirty or faulty flame sensor, faulty hot surface ignitor or burner problem may cause this. The furnace will lock out for one hour and then restart. 

CODE: 8 RED FLASHES 
RESULT: This fault is indicated if the flame is lost 5 times (4 recycles) during the heating cycle. 
FIX: This could be caused by low gas pressure, dirty or faulty flame sensor or faulty gas valve. The furnace will lock out for one hour and then restart. 

CODE: 9 RED FLASHES 
RESULT: Indicates reversed line voltage polarity or grounding problem. 
FIX: Both heating and cooling operations will be affected. check polarity at furnace and branch. Check furnace grounding. Check that flame probe is not shorted to chassis. 

CODE: 10 RED FLASHES 
RESULT: Flame sensed with no call for heat. 
FIX: Check gas valve and gas valve wiring This indicates that a primary or auxiliary limit switch has opened its normally-closed contacts and has remained open for more than five minutes. 

CODE: 11 RED FLASHES 
RESULT: This condition is usually caused by a failed blower motor or blower wheel. 
FIX: Cycle power (24 VAC) to the control to reset the hard lockout condition after correcting the failure condition. 

CODE: 12 RED FLASHES 
RESULT: This code indicates an open igniter circuit. 
FIX: This could be a disconnected or loose wire or a cracked or broken igniter. 

CODE: STEADY ON RED 
RESULT: Control failure. 
FIX: Replace control board. 

CODE: 60-MINUTE AUTOMATIC RESET FROM LOCKOUT 
RESULT: This control includes a "watchdog" type circuit that will reset from a lockout condition after 60 minutes. Operational faults 6, 7, 8 will be reset. This provides protection to an unoccupied structure if a temporary condition exists causing a furnace malfunction. An example would be a low incoming gas supply pressure preventing unit operation When the gas pressure is restored, at some point the "watchdog" would restart the unit and provide heat for the house. 

CODE: IGNITION CONTROL FLAME SENSE LEVELS 
RESULT: Normal flame sense current is approximately 3.7 microamps DC Low flame signal warning starts at 1.5 microamps. Low flame signal control lockout point is 0.1 microamps DC. 

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