Troubleshooting An AC That Blows Warm Air

It can be both frustrating and disappointing to turn on the AC on a hot afternoon to discover it does little more than blow hot air. There are several reasons why the AC may not be blowing cool air. The following troubleshooting guide can help you get to the root of the problem.

Issue #1: Thermostat troubles

The first step is to check the thermostat and make sure it is set to AC and not just fan. Try switching it off and then back to AC to see if this spurs it to send out cool air. Next, try turning down the temperature. If your thermostat isn't calibrated properly, you may need to set it for a lower temperature to get the cooling unit to kick on. If this doesn't work but the AC fan does seem to be popping on or running constantly, then you likely have one of the following issues.

Issue #2: Frozen condenser units

When an AC unit is not sized properly for the home, it will sometimes overwork and then freeze up. This occurs because condensation on the coils is building up faster than it can evaporate, which then causes it to freeze since it is in contact with cold condenser coils. Warm air can still circulate because the fan hasn't yet frozen up. Try turning off the unit until it thaws out completely, and then turn it back on. Try setting the temperature no lower than the low 70s to see if this solves the problem. If it continues to freeze, you may need to replace the unit with one more appropriately sized to your home.

Issue #3: A refrigerant leak

The refrigerant in an AC is supposed to be in a closed system, which means it shouldn't leak nor need to be replaced. Unfortunately, seals can give out and leaks can occur. You may not be able to spot a leak since it can be on the internal parts of the AC unit. You will need to bring in an AC professional, who can check the refrigerant level, find the leak, and repair it. They will then replace the refrigerant. Refrigerant is a toxic substance, so this isn't a recommended DIY repair.

Issue #4: Dying compressor

The compressor is where the cold air is created. As it begins to go out, you may still have hot air circulating from the fan but you won't have the compressor popping on to cool the air. You can usually tell if your compressor is out by listening – when the AC comes on you should hear the fan start up followed by a secondary motor sound as the compressor pops on. If you can't hear the compressor, call a local AC contractor to take a look at it to see if it can be repaired or if it needs to be replaced.