Heat Pump Not Heating? Defrost, Aux Heat and Reversing Valves

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Heat Pumps Feel Cooler by Design

A heat pump delivers supply air around 90 to 100 degrees Fahrenheit, which is warmer than the room but cooler than your skin, so it can feel like cool air even when the system is working perfectly. Before assuming failure, check that the supply air is clearly warmer than the return air.

Normal Defrost Versus a Real Problem

In cold damp weather a heat pump periodically reverses to melt frost off the outdoor coil, producing steam and a whoosh, and lasting five to fifteen minutes. That is normal. A solid block of ice encasing the coil, or ice that never clears, is a defrost board, sensor or refrigerant fault that needs service.

Auxiliary Heat Running Constantly

Electric strip heat is expensive backup, not primary heat. If AUX or EM HEAT is lit for hours in mild weather, you likely have low refrigerant charge, a stuck reversing valve, a failed outdoor sensor, or a thermostat configured for the wrong equipment type. Watch your electric bill, because this fault is quiet and costly.

Reversing Valve Failure

The reversing valve switches the refrigerant flow between heating and cooling. When the solenoid or valve sticks, you get cooling in winter, heating in summer, or a system stuck mid-shift. Diagnosis requires pressure and temperature readings on both sides of the valve, not guesswork.

Cold-Climate Heat Pumps

Modern inverter heat pumps hold capacity far colder than older units, and many operate efficiently well below freezing. If you are replacing an older heat pump in a cold climate, ask specifically about rated capacity at your design temperature rather than the headline SEER2 number.

Frequently Asked Questions

Why is my heat pump blowing cool air?

Either it is in a defrost cycle, the reversing valve is stuck, the charge is low, or the thermostat is calling for cooling. Compare supply and return air temperatures first.

Should I use emergency heat?

Only when the heat pump has genuinely failed, since EM heat is far more expensive to run. If you must use it, book heat pump repair right away.

Can ice damage the outdoor unit?

Yes. Ice on the fan blades or coil causes physical damage and restricted airflow, so persistent icing should be diagnosed quickly.

Do you install cold-climate heat pumps?

Yes, along with mini-split and ducted inverter systems, sized with a real load calculation.

Still stuck? Get a technician today

We run 24/7 emergency AC repair and heating repair with flat-rate pricing and same-day or next-day appointments. Call (888) 380-4427 or request service online.