Thermostat "Error 40"

Thermostat "Error 40"

THERMOSTAT FLASHING – Some York heat pumps and air conditioners utilize a computerized equipment monitoring system which will display an "Error 40" at the thermostat to indicate a problem or system malfunction.  Most alarms and alerts require a qualified service technician to diagnose.  However, there are some problems you may be able to resolve yourself.

* All diagnostics will attempt to reset by turning the thermostat "Off" for several minutes, and then back to "Heat" or "Auto".


No Power to the Outdoor Unit 

  • If there is no power to the outdoor unit for an extended period, the YorkGuard will generate a "Low Discharge Temperature" alarm and display "Error 40" at the thermostat.  Check the breaker for the heat pump and make sure that it is not tripped. Watch Video  If the breaker is okay, a qualified service technician should check the system.

Dirty Indoor Coil / Clogged Air Filter

  • A clogged filter, dirty indoor coil or restricted ductwork can cause a "High Pressure Fault" at the outdoor unit which will display an "Error 40" at the thermostat.

Refrigerant Issues - Qualified Technician Recommended

  • If a heat pump equipped with a YorkGuard module experiences a refrigerant issue that effects equipment operation, it will shut-off and display "Error 40" at the thermostat.

Bad Outdoor Fan Motor Qualified Technician Recommended

  • The outdoor fan motor should run any time the compressor is operating in the heating mode except during a defrost cycle.  If the compressor starts but the fan does not, either the motor or its starting capacitor is likely bad.

Bad Capacitor - Qualified Technician Recommended

  • Most direct-drive PSC fan motors require a capacitor which provides extra power for starting.
  • A fan motor with a bad capacitor will typically attempt to start but will fail while making a louder-than-normal humming noise.
  • After several seconds of humming, the motor will typically overheat and shut-off and then retry after about 30-60 seconds of cooling.
  • Sometimes a motor will still be able to start (with difficulty) with a bad capacitor.
  • A fan motor that runs normally after helping to start by turning by hand usually indicates a bad capacitor. 

Bad Compressor - Qualified Technician Recommended

  • The compressor in a heat pump pumps the refrigerant and provides the compression for heating and cooling to take place.  A compressor can have several malfunction conditions which can cause an "Error 40" code at the thermostat
  • A "shorted" compressor will usually cause the breaker to trip every time it tries to start. 
  • A "locked-up" compressor will typically fail to start.  It will often making a brief growling noise and may pull enough amperage to trip the breaker (a bad start capacitor can cause the same symptoms). 
  • A compressor with "bad valves" will generally start normally but will either produce very little or no compression.

Defrost Problem - Qualified Technician Recommended

  • If the YorkGuard sees a problem in the defrost sequence, it will display "Error 40" at the thermostat.  If the outdoor unit is severely frozen you should turn the thermostat to emergency heat and contact a qualified technician to diagnose.



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