heat pump troubleshooting
Heat pump is blowing cold air
What it probably is, what you can safely check yourself, and the point where it becomes our job.
It is still running, so you have a few days. It is not going to fix itself, and the part that failed rarely fails alone.
What is most likely going on
A few minutes of cool air during a defrost cycle is normal operation in a wet Whatcom winter. Air that stays cool through an entire call for heat usually means the system is not actually in heating mode, the charge is low, or the reversing valve is not shifting.
Likely causes, most common first
- 1
It is in a defrost cycle
When the outdoor coil frosts, the system briefly reverses to melt it and the indoor air goes neutral or cool for several minutes. You will see steam rolling off the outdoor unit and hear the reversing valve change position. At 35°F and near-saturated air, which is most of a Bellingham January, this happens regularly and is not a fault.
- 2
Thermostat is in cooling or on “auto” with a low setpoint
A thermostat set to cool, or set to auto with a heating setpoint below room temperature, will run the compressor in the direction you did not want. This is the single most common cause we find on a first heating-season call, and it is free to rule out before anyone drives out to you.
- 3
Reversing valve stuck or not being energised
The reversing valve is what makes a heat pump a heat pump rather than an air conditioner. If the valve solenoid is not being commanded, or the valve itself has stuck mid-position, you get cooling or lukewarm air on a call for heat. This is a diagnostic that requires gauges and a meter on a live system.
- 4
Low refrigerant charge from a leak
A leaking sealed system loses capacity gradually, so supply air gets progressively less warm across a season rather than failing all at once. Adding refrigerant without finding the leak is not a repair, it just resets the clock. Any work inside the refrigerant circuit is federally regulated under EPA Section 608.
- 5
Indoor blower running with the compressor locked out
If the compressor is off on a safety or a lockout while the blower keeps running, you get room-temperature air moving through the house, which reads as cold. Backup lockout settings can also be involved: PSE’s rebate requires resistance backup to be locked out via an outdoor sensor, so a misconfigured sensor can leave you with fan-only air.
What you can safely check yourself
Work down the list before you book anything. Plenty of calls end here, and we would rather you keep the money.
- Confirm the thermostat is set to Heat, not Cool or Auto, and that the setpoint is at least a couple of degrees above the current room temperature.
- Confirm the thermostat is not sitting in emergency or auxiliary heat mode from a previous cold snap.
- Time it: if warm air returns within roughly ten minutes and the outdoor unit was steaming, you watched a normal defrost cycle.
- Check the indoor filter and replace it if light will not pass through it, since a starved blower reduces supply temperature.
- Check the breaker for the air handler and the outdoor unit, and the disconnect box at the outdoor unit, for a tripped position.
What is deliberately not on that list
Nothing above involves refrigerant, gas piping, or opening a live electrical panel. Refrigerant work is federally regulated and needs recovery equipment. Gas work done wrong kills people. An energised panel turns a $300 repair into a hospital visit. Electrical work on the circuit itself is done by a licensed electrical contractor. If a step you have read elsewhere involves any of those three, stop and call instead.
When to call us
Call us if the supply air never gets warm across a full cycle, if warm air has been getting weaker week over week, or if the outdoor unit runs while the indoor air is unchanged. Reversing valve and charge diagnostics need gauges on a running system. Regular hours are Monday–Friday 8:00 AM–5:30 PM at (360) 592-3824, and emergency calls are answered 24/7.
Monday–Friday, 8:00 AM – 5:30 PM · Emergency calls answered 24/7
Tell us what it is doing
Describe the symptom and we will tell you what it takes to fix, what it is likely to cost, and whether it is worth fixing at all.
Monday–Friday, 8:00 AM – 5:30 PM · Emergency calls answered 24/7