Air Conditioner / Heat Pump Won't Stop

A/C or Heat Pump Runs Normally but won't shut off when the thermostat set temperature is reached

When your A/C Won't Stop, Identify which Components Are Still Running:

1. Indoor Blower Fan Keeps Running After Thermostat is Satisfied

Check first that someone has not set one of the system controls to force the air handler fan to run continuously.

The indoor air handler blower can be forced to keep running, as we explain at

• BLOWER FAN WONT STOP - LIMIT SWITCH
• BLOWER FAN WONT STOP - THERMOSTAT SWITCH

If your indoor air handler blower fan in the INSIDE AIR HANDLER was not running, I would not expect any significant airflow through the ductwork.

2. Outside Condenser Unit Won't Stop Running

The outdoor condenser unit compressor motor may turn on and off from time to time while the fan may run for a longer interval. The compressor motor itself may be harder to hear under the fan's own noise but it's there.

Under a heavy continuous cooling load, an air conditioning or heat pump system might run a lot or even continuously. The compressor motor and the fan may both run continuously in that case.

Watch out: But if you set your indoor thermostat well above the current indoor temperature AND the thermostat is in COOL mode AND if the air conditioner system never shuts down, then something's wrong and repair is needed.

Watch out: Similarly, if the A/C system runs continuously, including both the indoor air handler and outdoor compressor/condenser unit, but the system cannot ever cool the building enough to allow the thermostat to turn off the system, then your system might be under-sized for the building's cooling load, or it may need repair.

More help is at A/C or HEAT PUMP RUNS, NO COOL AIR DELIVERED - in cooling mode

If your outside compressor/condenser unit fan keeps running it's possible that that's normal IF the compressor was working also.

Watch out: If the compressor shuts down and the outdoor condenser fan keeps running for more than a few minutes, we suspect that there is a bad switch or control board in the system.

In that case, call for repair.

Details are at CONDENSER FAN WON'T STOP

3. Outdoor Compressor/Condenser Unit Fan Keeps Running After Thermostat is Satisfied

This can be normal as the fan's control circuit may leave it on for a time to cool down the outdoor coil and condenser unit at the end of a cooling cycle.

If the outdoor compressor/condenser unit isn't working (it may be running but the system could be out of refrigerant, or it may not be running at all), the indoor air handler may run but in cooling mode you'd get just warm air flow out of your A/C supply registers.

Watch out: But if the outdoor fan never stops running and your thermostat is satisfied and the indoor air handler has shut down, something's wrong at the outside unit and you need to call for repair.

4. Outdoor Compressor/Condenser Unit Compressor Runs but Outdoor Fan Never Turns On

Watch out: If the outdoor compressor condenser keeps running but the cooling fan on the outdoor unit never turns on, then you should leave the system turned OFF and call for repair.

We describe that problem and its repair at CONDENSER FAN WON'T START

A/C or Heat Pump Runs, In Cooling Mode, No Cool Air Delivered

If your air conditioner or heat pump system outdoor compressor/condenser unit is running but no cool air is flowing out of the air supply registers in the building, then either the indoor air handler blower fan isn't working or it is running but there is a duct blockage or ducts are disconnected somewhere.

If the indoor air handler/blower unit is not running, see

A/C BLOWER UNIT / FURNACE FAN WONT START

and

BLOWER FAN OPERATION & TESTING

Check next for a very dirty air filter or blower fan assembly that blocks air flow through the system.

Look also for a frost or ice-blocked cooling coil in or at the air handler.

See FROST BUILD-UP on AIR CONDITIONER COILS

If that's not the problem, follow the ductwork to look for a ductwork damper that is closed or ducts that have collapsed, been crimped, or are disconnected.

If your air conditioner is running at the indoor air handler/blower unit and air is flowing out of the supply registers but the air is not cool, check to see if the outdoor compressor condenser unit is running.

If the outdoor condenser unit is not running,

see AIR CONDITIONER WON'T START

If the outdoor condenser unit is running and air flows from the supply registers indoors but the air is not cool, we suspect that the system has lost virtually all its refrigerant.

Less likely but possible, the system heat pump is stuck in "heat" mode and is not switching to "cooling" mode. That problem could rest with a bad control board, relay, or thermostatic expansion valve (TEV) - it's time to call for help from your HVAC service company.

See the diagnostics at

AIR CONDITIONER BLOWS WARM AIR

Heat Pump In Heating Mode, No Warm Air Provided

When your thermostat is calling for heat and both the heat pump outdoor condenser unit and the indoor air handler blower unit are running and air flows from the supply registers indoors but the air is not warm (and we are in HEAT mode), we suspect that

Outdoor temperatures are too cold for the heat pump to work and

the backup heat provided indoors for your system is not working.

That problem could rest with a bad control board, relay, or thermostatic expansion valve (TEV) - it's time to call for help from your HVAC service company.

Less likely but possible, the system is a heat pump stuck in "cool" mode and is not switching to "heating" mode.

See these diagnostics

• HEAT PUMP DIAGNOSTIC GUIDE
• HEAT PUMP OUTDOOR UNIT DEFROST CYCLE
• HEAT PUMP THERMOSTAT, OUTDOOR
• REVERSING VALVE on HEAT PUMPS