AC Blowing Warm Air: What to Check First

An AC blowing warm air has either a control or airflow problem, or a problem in the sealed refrigerant side of the system. The first kind you can often find yourself in a few minutes. The second kind needs a licensed HVAC professional with gauges and a meter, and guessing at it wastes time. This page walks you through the checks that tell the two apart, then explains how One Call Home Pros connects you with a vetted, insured local pro if the checks do not solve it.

The short answer

Warm air from the vents means the indoor fan is running but the air is not being cooled as it crosses the indoor coil. Either the system is not being told to cool, or the outdoor unit is not removing heat from the refrigerant.

The quickest clue is the outdoor unit. If it is silent while the indoor fan blows, the problem is usually power, a safety switch or the controls. If it is running but the air stays warm, the problem is more often refrigerant, the compressor or a dirty coil.

What to check first

Work through these in order. Each one is safe, and each one rules out a common reason for an AC blowing warm air.

1. The mode. Make sure the thermostat says cool, not heat or fan only. Many Florida systems are heat pumps, and a thermostat bumped to heat will blow warm air on purpose.
2. The fan setting. If the fan is set to on rather than auto, it keeps blowing between cooling cycles. That air feels warm. Set it to auto and wait for the next cycle.
3. The set temperature. It needs to be below the room temperature for the system to call for cooling.
4. The filter. A filter caked with dust starves the coil of air and can freeze it. Replace it if light does not pass through.
5. The breakers and the outdoor disconnect. The outdoor unit often has its own breaker and a disconnect switch beside it. Either can be off while the indoor fan still runs.
6. The condensate safety switch. If water has backed up in the drain pan, a float switch may have shut down the outdoor unit while leaving the fan on.

Reading what the outdoor unit is doing

Stand near the outdoor unit while the thermostat is calling for cooling.

• Silent. Power is not reaching it, a safety switch has cut it out, or the thermostat signal is not getting through. A failed contactor also leaves it silent.
• Humming, fan not spinning. A failed capacitor or a seized fan motor is a common cause. Turn the system off at the thermostat. A compressor that keeps trying to start in this state overheats.
• Fan spinning, air still warm. The compressor may not be running, or the system may be low on refrigerant. A coil packed with dirt can also stop it shedding heat.
• Clicking on and off. The unit may be short cycling on a safety, which the pro needs to trace.

When to stop and call a pro

The checks above stop at the outside of the equipment. Past that point, leave it to a licensed professional. Do not open the outdoor unit’s service panel, where the capacitor holds a charge after the power is off. Do not touch the service ports or caps on the copper lines. Do not add refrigerant from a store-bought kit, and do not hose down the inside of the unit with the power on.

Turn the cooling off and call if the outdoor unit hums without spinning, if ice forms on the lines, if a breaker trips a second time, or if you smell something burning.

Duct problems: warm air in one room only

If most rooms are cool and one is not, the equipment may be working fine. In many South Florida homes the ducts run through a very hot attic. A duct that has come loose, split or been crushed blows conditioned air into the attic and pulls hot attic air into the room. Closed or blocked vents in that room do the same in a milder way. Tell the pro if the problem is limited to one area. It changes where they start looking.

What the pro checks

An HVAC professional looking at an AC blowing warm air usually works from the controls outward:

• The thermostat signal and wiring at both the indoor and outdoor units
• The capacitor, contactor and fan motor in the outdoor unit
• Whether the compressor is starting and drawing normal current
• Refrigerant pressures and temperatures, to confirm or rule out a leak
• The condition of the indoor and outdoor coils
• The ductwork, if only part of the house is affected

Low refrigerant means a leak. A pro who only adds refrigerant without looking for the leak leaves you with the same problem later.

How One Call fits in

One Call Home Pros does not hold an air conditioning licence and does not touch the equipment. When you call, tell us what the outdoor unit is doing, what the thermostat is set to and what you have checked. We match you with a vetted HVAC pro who is licensed and insured for repair work. The pro finds the fault, explains it in plain terms and fixes it. One Call vets the pro, arranges the visit and stays with the job until it is right.

You pay One Call, and One Call pays the pro. Before the repair starts, ask what the price includes. More about AC repair is on the service page, and there are pages for AC repair in Sunrise, Tamarac and Hollywood.

Get the cooling back

If the checks did not find it, switch the cooling off and tell One Call what the system is doing. We match you with a vetted, licensed local HVAC pro.