Fan Doesn’t Run
- Category: Common HEAT PUMP Heating Issues
- Published: 21 November 2013
FAN DOESN'T RUN – There is no air blowing out out the supply registers, resulting in "no heat".
- If the indoor fan motor does not operate when the heat pump is running, the outdoor unit will generate very high pressure and will either lock-out on a high-pressure switch or become very noisy.
- If you notice the fan motor not operating when the heat pump is on, you should turn the system "Off" until the problem is resolved.
POSSIBLE PROBLEM & DESCRIPTION
Thermostat Set Incorrectly
- Many "no heat" calls, especially early in the heating season are the result of thermostats that are not set correctly. Make sure the system setting is set for either "Heat" or "Auto" and the desired temperature is set higher than the space temperature.
Loss of Power to the Air Handler
- 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.
- A less likely, but possible, cause is a bad thermostat. It is possible for the thermostat to fail to energize the heating or fan outputs.
- Try turning the Fan switch to the "On" position to see if the blower comes on. Watch the video. If the blower operates in the "On" position and does not operate when the heat pump is running, you may have a bad thermostat.
- If you have an electronic thermostat, you may also want to try installing new batteries.
Bad Blower Motor - Qualified Technician Recommended
- If the blower motor does not start when the heat pump comes on (no air blowing out of the registers), it could be the result of a bad blower motor.
- One diagnostic step that can be taken is to turn the fan to the “On” position at the thermostat. If the fan operates, this would indicate that the problem is most likely something other than the fan motor. It may be necessary to leave the fan in the "On" position so the heat pump can continue to operate until the problem is resolved.
- If the fan does not operate automatically, or after turning the thermostat fan switch to the "On" position, this may indicate either a bad blower motor or a bad capacitor (below).
- A failed blower motor will often be accompanied by a bad odor (like burning plastic or rubber).
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.
Control Board - Qualified Technician Recommended
- Most newer gas furnaces and air handlers use a computerized control board to activate the blower motor. The control board should start the blower motor immediately on a call for heating or cooling.