Heat Pump Blowing Cold Air in Heat Mode? Normal Operation vs. a Fault

Put your hand over a register fed by a gas furnace and the air is hot. Do the same with a heat pump and it may feel barely warm, or even cool. Carrier puts typical heat pump supply air at around 85 to 100°F and gas furnace air at roughly 120 to 140°F. Trane’s figure for a heat pump is 85 to 93°F, and it makes the point that this feels cool because your body is at 98.6°F.

So the first question is not what the air feels like. It is whether the house is reaching the temperature you set.

Normal, or a fault?

Check it in this order

1. Read the thermostat.Safe check

   The mode should be Heat and the fan should be Auto. Trane notes that with the fan set to On, the system blows air even when the heat pump is not heating. If the screen shows Defrost, Trane’s advice is to wait: heating resumes when the cycle ends.

2. Raise the setting and listen.Safe check

   Lennox suggests raising the temperature by at least 5 degrees and listening for the system to start. If nothing happens, check the thermostat’s batteries. More in thermostat not working.

3. Look at the air filter.Safe check

   Hold it up to a light. If you cannot see through it, replace it with the same size. Trane says to change standard filters every 1 to 3 months; Carrier says to check every 60 to 90 days.

4. Clear the outdoor unit.Take care

   Lennox says to switch off the power at the disconnect box beside the unit first, then gently remove leaves, dirt or snow from around and on top of it, and switch the power back on. Never chip at ice: see a heat pump freezing up.

5. Check the breakers and switches.Take care

   Carrier points out that the outdoor unit and the indoor unit have separate breakers, and that there is a disconnect near the outdoor unit and a switch at the indoor air handler. Reset a tripped breaker once. If it trips again, stop and call a professional.

6. Still cold after all of that?Technician

   The remaining causes are sealed-system and control faults. Lennox’s rule: never open panels on the heat pump, touch refrigerant lines or handle electrical components beyond resetting a breaker.

What a defrost cycle looks like

In heating mode the outdoor coil runs colder than the outdoor air, so frost forms on it in cold, damp weather. To clear it, the heat pump switches to a defrost mode. Lennox says some units defrost on demand and others on a timer set to 30, 60 or 90 minutes, and that a cycle usually lasts 5 to 15 minutes, during which the system blows cooler air. Carrier describes this as a normal function.

A defrost cycle that ends with the frost gone is the system looking after itself. Ice that is still coating the unit afterward is on Lennox’s list of reasons to call a technician.

When to call a technician

Lennox’s list:

• Cold air continues after the checks above.
• Heavy ice on the outdoor unit does not clear after a defrost cycle.
• Grinding, squealing or banging noises.
• The system turns on and off repeatedly without reaching the set temperature.
• Error codes or warning lights on the thermostat or the equipment.
• A burning smell, smoke or any electrical problem.
• Energy bills that jump with no explanation.

Carrier adds one more: if the room is consistently more than 2 to 3°F away from the thermostat setting, have the thermostat and system checked.

If the heat pump is old and the repair is a major part, the repair or replace calculator weighs the repair bill against the unit’s age. If your thermostat is the part behaving oddly, see a thermostat that keeps changing temperature. For a gas or electric furnace, the checks are different: see a furnace blowing cold air.

To see what your heat pump costs to run for heating and cooling, read the cost of running a heat pump.