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AC not heating: first find out what you actually own

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Plain air conditioners do not make heat. Before you troubleshoot, work out whether your system is supposed to heat at all.

If your AC is not heating, the first question is whether it was ever meant to. A standard central air conditioner only cools. The heat in a house like that comes from a furnace, a boiler or electric strip heaters, not from the AC.

So check what you own before you chase a fault.

Is it an air conditioner or a heat pump?

Look at the outdoor unit's data label and at your thermostat. A heat pump is labeled as one, and its thermostat usually offers an emergency or auxiliary heat setting. A cooling-only unit has no such mode. If your label says air conditioner or condenser only, the outdoor unit will never produce heat, and that is normal.

In that case the thing to check is the furnace. See our guide on a furnace that will not turn on.

If you have a heat pump, start with the thermostat

Set it to heat, with the setpoint a few degrees above the room temperature. A system left in cool or auto-changeover mode will happily blow cool air. Replace the batteries if the thermostat uses them. This fixes more complaints than you would expect.

Cold air in heat mode is not always a fault

A heat pump delivers air that feels cooler than a furnace does, because it is warmer than the room but well below skin temperature. That alone is not a failure. A defrost cycle in cold, damp weather can also blow cooler air for a few minutes. If the house keeps losing ground for hours, though, something is wrong.

Check filters and airflow

A clogged filter or blocked vents choke the airflow, and the system cannot move its heat into the rooms. Swap a dirty filter and make sure the supply registers are open. This is cheap and safe to do.

Look at the outdoor unit from a distance

With the system calling for heat, check whether the outdoor fan is running. Leaves, snow or heavy ice around the cabinet can stop it. Clear loose debris from the outside, but do not chip at ice with tools and do not open the cabinet.

What not to do

  • Do not remove panels or touch the wiring or capacitor inside the outdoor unit. A capacitor can hold a dangerous charge even when the power is off.
  • Do not try to add or check refrigerant. Federal law requires EPA Section 608 certification, and it is illegal without it.
  • Do not keep resetting a breaker that trips again.

When to call a licensed HVAC technician

Call one if you own a heat pump and it still blows cool air after the thermostat, filter and airflow checks. Call one too if a breaker trips again, or if a heat pump shows no sign of ever heating. If you smell gas or a carbon monoxide detector sounds, leave the house and call the gas company or 911 instead.

Frequently asked questions

Why is my AC not heating the house?

A standard central air conditioner only cools. If you have one, heat comes from a furnace or boiler. If you have a heat pump, check the thermostat mode, the filter and the outdoor fan first.

How can I tell if I have a heat pump or an AC?

Check the label on the outdoor unit and the thermostat. A heat pump is labeled as one and often has an auxiliary or emergency heat setting. A cooling-only unit does not.

Can I fix a heat pump that blows cool air in heat mode myself?

You can check the thermostat, the filter and the airflow. Anything inside the unit is electrical and refrigerant work and must be done by a licensed technician.

Sources

What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.

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