Why Is My AC Blowing Warm Air?
An AC blowing warm air usually has the fan set to ON, an outdoor unit with no power, or a refrigerant leak. Set the thermostat to COOL and the fan to AUTO. Then go outside and check that the outdoor unit is actually running. If the inside fan blows but the outdoor unit is silent, check that breaker once.
What makes an AC blow warm air?
Thermostat fan set to ON
With the fan on ON, the indoor blower runs all the time and pushes room-temperature air out of the vents between cooling cycles. That air feels warm even though nothing is broken. Move the fan to AUTO so it runs only during cooling. It takes a minute and it is safe.
Safe to check yourselfOutdoor unit lost power
If the breaker for the outdoor unit has tripped, the indoor fan keeps moving air while the outdoor unit sits dead. The vents then blow warm. Check the breaker panel and reset a tripped breaker one time only. If it trips again, leave it off and call.
Safe to check yourselfRefrigerant leak
Refrigerant is the fluid that carries heat out of your house. As it leaks away, the system moves less and less heat, and the air gets warmer week by week. You may also see ice on the copper lines. Finding a leak takes gauges, a license, and a pressure test.
Technician repairDirty air filter
A badly blocked filter can freeze the indoor coil. Once that coil is a block of ice, the air going past it barely cools at all. The vents then blow weak, warmish air. Checking the filter and changing it takes a few minutes and is safe.
Safe to check yourselfBlocked outdoor unit
An outdoor unit buried in leaves, cottonwood fluff, or shrubs cannot get rid of heat, and the cooling falls off badly on hot days. Clearing debris and cutting plants back two feet is safe to do yourself. Washing the fins is our job.
Safe to check yourselfStuck valve on a heat pump
A heat pump uses one valve to switch between heating and cooling. When that valve sticks in heating, the system really does blow warm air on a cooling call. Getting to it means opening the sealed refrigerant side, so it is a technician repair.
Technician repairDucts pulling in hot attic air
Ducts that leak up in a hot attic mix attic air into what comes out of your vents. The AC is working, but the air reaching you is warmer than it should be. We find the leak and show you where it is, so you know what is really behind the warm air.
Technician repairWhat can you check yourself?
- Set the thermostat to COOL, the fan to AUTO, and the temperature several degrees below the room.
- Stand at the outdoor unit and check that the fan on top is spinning while the thermostat is calling for cooling.
- If the outdoor unit is silent, check its breaker and reset it one time only.
- Look at the air filter and change it if it is dirty.
- Clear leaves, grass, and debris away from the outdoor unit on all sides.
Safety note: Reset the outdoor unit breaker one time at most. A breaker that trips again is protecting you from an electrical fault, and it should stay off until a technician checks it.
When should you call for repair?
Call when the thermostat is set right, the outdoor unit is running, the filter is clean, and the vents still blow warm. Call sooner if you see ice on the copper lines. Call if the outdoor breaker trips more than once. Call if a heat pump blows heat when you asked for cooling. Warm air with everything apparently running usually means a refrigerant or valve problem, and both need a licensed technician.
Nearly every street in North Potomac is two-story colonials from the 1980s and 1990s, running on one system sized for the whole house. Upstairs runs warm in summer. Plenty of these homes had the equipment swapped once and the ductwork left exactly as it was, so the split never went away. Warm air upstairs is usually a duct and return problem, not a broken AC. Warm air from every vent in the house is a different problem, and that one points at the equipment.
Related questions
Why does my AC blow warm air when it first turns on?
A minute or two of warm air at startup is normal. The blower first pushes out the air that was sitting in the ducts, and a heat pump may take a moment to settle before cooling starts. If the air is still not cool five minutes after the outdoor unit is running, that is no longer startup and it needs a look.
Why is the inside fan blowing but the outdoor unit is not running?
That means the indoor unit has power and the outdoor one does not. The usual causes are a tripped breaker, a failed capacitor, or a burned contactor. Check the breaker and reset it once. If the outdoor unit still will not start, or the breaker trips again, stop there and book a visit.
Can a dirty filter make an AC blow warm air?
Yes. A badly clogged filter cuts the airflow enough to freeze the indoor coil, and once ice forms the air going past barely cools. The vents then blow weak, warmish air. Change the filter, switch the system to OFF with the fan on to melt the ice, then restart. If warm air comes back with a clean filter, the cause is deeper.
Is warm air always a refrigerant problem?
No. Thermostat settings, a tripped breaker, a clogged filter, and a blocked outdoor unit cause most warm-air calls, and three of those are safe to check yourself. Low refrigerant is on the list, but it is what is left after the simple causes are ruled out. That is the same order a technician works through.
If the vents are still blowing warm after these checks, call Mora Heating & Air and we will get the cooling back.
Or tell us what your system is doing
Send us the details and we will call you back. If the house is very hot or very cold right now, calling is faster.