Sometimes Doesn’t Heat
SOMETIMES DOESN'T HEAT – Most of the time the system heats correctly, but sometimes it blows cool air and the temperature in the space drops below the heating setpoint.
POSSIBLE PROBLEM & DESCRIPTION
Clogged Air Filter/Dirty Coil/Restricted Ductwork
All new York air handlers have a feature which disables the auxiliary heaters if the over-temperature device is activated three times during a run cycle. This "lock-out" also energizes the fan to run continuous until manually reset.
The most common cause of this failure is low airflow across the heaters. The most common source of low airflow is a clogged air filter, but can also be caused by a dirty indoor coil or closed/restricted ductwork.
Once the source of the airflow restriction is eliminated, reset the lock-out by cycling high-voltage power to the air handler.
Thermostat Set Incorrectly
If you have a new electronic thermostat it may be set to run a schedule and maintain different temperatures at different times. The thermostat should show the current temperature setpoint as well as the current space temperature.
When the systems is not heating, check the thermostat and the current heating setpoint.
Loss of Power to Auxiliary Heaters
Many air handlers have more than one breaker that provide power. For instance, on an air handler with 15kw heaters, one breaker powers the blower and one heater while another breaker powers the remaining two heaters. Check the breaker panel and the air handler itself for any tripped or turned-off breakers.
This problem may show itself only during extremely cold outdoor air conditions when all stages of heat are required.
Return Ductwork Issues
If the return duct system has openings or has come loose (especially in an unheated attic or crawlspace), it will draw-in cold air and, even if the heat pump is operating normally, blow cool air from the supply registers and may not heat the space.
This condition is easiest identified by checking the return air temperature entering the air handler. An extremely cool return air temperature would indicate ductwork problems.
This problem may show itself only during extremely cold outdoor air conditions.
A less likely, but possible, cause is a bad thermostat. We have seen instances on newer electronic thermostats where the relay outputs fail to energize the auxiliary heaters even though the thermostat display shows that "Heat" is activated.
Failed Auxiliary Heater Controls - Qualified Technician Recommended
All air handlers have some type of control to energize the auxiliary heaters. Most newer air handlers use an electronic control board to cycle the heaters. Older air handlers use mechanical heat sequencers to power the heaters. It is not uncommon for control boards and sequencers to fail over time.
Heat Pump Lockout - Qualified Technician Recommended
Some York heat pumps incorporate a YorkGuard module which monitors equipment operation. If the Yorkguard senses an abnormal condition which could possibly harm the system it will enter a lock-out mode which disables the heat pump.
If wired-in, the Yorkguard should give an alert indication at the thermostat.
A lock-out can be reset by turning the thermostat to the "Off" position and then back to "Heat" or "Auto".