Why your heat pump is not heating or cooling

Written by the team at Panda Heating and Cooling · licensed TDLR TACLA128438C · published 5 September 2026

First: lukewarm air is often normal

More heat pump calls turn out to be this than any actual fault, so it is worth settling before anything else.

A gas furnace blows air at 120–140°F. It feels hot on your hand. A heat pump blows at roughly 90–95°F — warmer than the room, cooler than your skin. So it feels like cool air even while it is heating your house perfectly.

The test is not your hand, it is the thermostat. If the room temperature is climbing toward the setting, the system is working. If it is not moving after an hour, something is wrong.

This catches people who moved from a gas furnace to a heat pump, and it catches people new to Texas from colder states. Nothing is broken; it is a different machine.

Defrost mode looks exactly like a fault

On a cold damp morning your outdoor unit will ice up — that is physics, not a failure. Every so often the system deliberately reverses itself to melt that ice off.

During defrost, which lasts a few minutes, you will see: steam rising from the outdoor unit (often mistaken for smoke), the outdoor fan stopping, a loud whoosh as the reversing valve changes over, and cool air indoors until it finishes.

All of that is correct behaviour. Call us if it happens constantly, if the unit stays encased in ice, or if the ice never clears — that is a stuck defrost board, a failed sensor, or low refrigerant. A few minutes every hour or so on a damp morning is the system working.

Auxiliary heat, and the bill that comes with it

Below roughly 35°F a heat pump struggles to pull enough warmth from outdoor air, so a backup kicks in — usually electric resistance strips. Your thermostat may show AUX or EM HEAT.

Auxiliary heat works, and it is expensive. It is meant for the coldest hours of the coldest days, not all winter.

If AUX is showing at 50°F, something is wrong. The heat pump itself is not doing its share — low refrigerant, a failing reversing valve, or a thermostat set to Emergency Heat and left there. That last one is common and it is free to fix: check your thermostat is on Heat, not Em Heat. People switch it during a freeze and forget.

The six real faults

Once the above is ruled out, it is one of these — and they need gauges.

• Low refrigerant. A heat pump moves heat in both directions, so a leak shows up as poor heating and poor cooling. If both seasons feel weak, start here.
• A failing reversing valve. The part that makes a heat pump a heat pump. When it sticks you get one mode only — cooling in January is the classic symptom.
• A failed defrost control board. The unit ices up and never clears.
• A capacitor or contactor. Same cheap electrical parts as any AC, same humming-but-not-starting symptom.
• A dirty outdoor coil. A heat pump depends on that coil in both directions, so dirt costs you twice.
• Auxiliary heat strips that have failed. The heat pump works, the backup does not, and you notice on the first hard freeze.

After a power cut

“Heat pump not working after a power outage” is a search in its own right, and there is a simple reason.

Many heat pumps have a built-in delay — often five minutes — before the compressor restarts, to protect it from starting against high pressure. After a cut, wait ten minutes before deciding anything is wrong.

If it is still dead after that, check the breaker and the outdoor disconnect box. If the thermostat is blank, its batteries may have been running the display and gone flat. Beyond that it needs looking at — a surge can take out a capacitor or a control board, and that is a same-day repair.