Quick checks before anything else
A heat pump that runs but doesn’t cool usually has one of a handful of problems. Some are simple, and some involve refrigerant or high-voltage parts that only a licensed technician should handle. Start with the easy items:
- Thermostat mode. Confirm it is set to Cool (not Heat, Emergency Heat or Fan Only; see heat pump fan: on or auto for the fan setting) and the set temperature is below the current room temperature.
- Power. Check that the thermostat display is on and that the breaker for the indoor unit and the outdoor unit hasn’t tripped.
- Filter. A clogged filter is one of the most common causes of poor cooling.
- Give it time. Many systems wait a few minutes after being switched on or changed before the compressor starts. This delay protects the compressor.
Common reasons a heat pump isn’t cooling
Thermostat settings or thermostat problems
A thermostat set to heat, set to a temperature that is too high, or with dead batteries can look like a failed system. If the settings are right and the system still does not respond to the thermostat, see our guide to a heat pump thermostat that isn’t working.
Dirty air filter and blocked airflow
A dirty filter, closed or blocked vents, and blocked return grilles reduce the air moving across the indoor coil. Less airflow can mean weak cooling and, in some cases, a frozen coil. Replace the filter if it looks clogged and make sure registers are open and not covered by furniture or rugs.
Dirty or blocked outdoor unit
In cooling mode the outdoor unit has to release heat. Leaves, grass clippings, cottonwood fluff, a covered unit or plants growing too close can restrict airflow. Switch the system off first, then clear debris from around the unit. A light rinse with a garden hose from the outside can remove surface dirt, but do not use a pressure washer, which can bend the fins. If the coil is heavily caked, a technician can clean it.
Frozen coil
Ice on the indoor coil or on the copper line outside blocks airflow and stops cooling. Turn the system off and let the ice melt completely before restarting. A restricted filter is a common cause, but low refrigerant can also be behind it. See why a heat pump freezes up in summer.
Low refrigerant
A heat pump uses a sealed refrigerant circuit, so it normally does not “use up” refrigerant. If the level is low, there is typically a leak. Signs include warm air, ice, hissing sounds and longer run times, though these also have other causes. Our article on how to tell if a heat pump is low on refrigerant covers the signs in more detail. Refrigerant work requires certification in many places, so this is a job for a licensed technician, not a DIY top-up.
Electrical parts: capacitor, contactor, breaker
If the indoor fan runs but the outdoor fan or compressor does not, a failed capacitor, contactor or compressor may be the cause. These parts can hold a dangerous electrical charge even when the power is off. Do not open electrical panels on the outdoor unit unless you are qualified. If the breaker trips repeatedly, see why a heat pump breaker keeps tripping.
Reversing valve stuck
Heat pumps use a reversing valve to switch between heating and cooling. If it sticks, the system may keep delivering heated air while set to cool. This is a repair for a professional.
Short cycling or a poorly sized system
A system that turns on and off every few minutes may not remove enough heat or humidity (see AC cooling but not removing humidity). Causes range from airflow restrictions to thermostat placement to an oversized unit. See heat pump short cycling for details.
A step-by-step troubleshooting order
- Check thermostat mode, set point and batteries.
- Check breakers and any visible switch near the indoor unit.
- Inspect and replace the air filter if dirty.
- Open all registers and clear return grilles.
- Look at the outdoor unit: is the fan spinning, and is the coil clear of debris?
- Look for ice on the indoor coil area or the refrigerant lines. If you see ice, turn the system off and let it thaw.
- Wait several minutes and test again.
If the problem remains after these steps, stop and call for service rather than continuing to experiment.
What you can safely do yourself
- Replace or clean the filter.
- Adjust thermostat settings and replace thermostat batteries.
- Clear leaves and debris from around the outdoor unit with the power off.
- Open and uncover vents and returns.
When to call a professional
Call a licensed HVAC technician if:
- You suspect low refrigerant or a leak. Do not try to add refrigerant yourself.
- The outdoor fan or compressor will not start, or you hear humming, clicking or grinding.
- The breaker trips repeatedly. Do not keep resetting it.
- You smell burning or see scorched wiring, or notice signs of an electrical problem. Turn the system off at the breaker and call right away.
- Ice returns after you’ve replaced the filter and thawed the coil.
Preventing cooling problems
Replace or clean filters on the schedule your manufacturer recommends, keep the outdoor unit clear, and have the system inspected once a year. A yearly check lets a technician look at refrigerant pressures, electrical components and coil condition before hot weather.
FAQ
Why isn’t my heat pump working properly? The most common causes are thermostat settings, power or breaker problems, dirty filters, a blocked outdoor unit, ice, and component failures such as a capacitor or fan motor.
Why is the air from my vents not cold? Check for the wrong thermostat mode, a dirty filter, ice and a dirty outdoor coil. If those are fine, low refrigerant, a stuck reversing valve or a compressor problem may be involved, and a technician should diagnose it.
Is there a rule on when to replace instead of repair? Some contractors use rules of thumb involving repair cost and system age, but they are only rough guides. Ask for a written estimate and compare it with replacement cost, system age, and the refrigerant type your system uses.