May 15, 2023
8 Common HVAC Emergencies and How to Handle Them

Even if your AC unit is old and not working correctly, it should still always blow out at least some cold air whenever the system is on. When an AC starts blowing warm air, it usually means that something is wrong, but other issues may be to blame. If your AC is making your home hotter, consider some of these potential causes.

1. Incorrect Thermostat Setting

If you ever notice that warm air starts blowing out of your vents any time when your thermostat is set to AC, the first thing to do is check the fan setting on the thermostat. The fan should always be set to “Auto” and not “On.” If the fan is set to “On,” it will run continuously even after the AC condenser unit outside shuts off.

When the AC condenser is running, it constantly supplies cooled refrigerant to the evaporator coil inside the building. At the same time, the AC blower pulls warm air in, and the refrigerant absorbs much of the heat from the air. If the fan is set to “On” and continues to run after the condenser shuts off, it will continually pull warm air in and then blow that warm air out of all the vents. This is why the fan should always be on the “Auto” setting when your AC is on.

2. Frozen Evaporator Coil

The most common reason that an AC system will start blowing warm air is because the evaporator coil is frozen. Air conditioners don’t just remove heat from the air, but they also absorb moisture. As warm air comes into contact with the cold evaporator coil, moisture condenses on the coil and then drips down into the condensate drain system. If the refrigerant is colder than it should be or the blower isn’t drawing enough warm air into the system, the condensation that collects on the coil can start to freeze and a thick layer of ice can start to form on the coil.

When the evaporator coil is frozen, the system can no longer absorb any heat and the fan will simply start circulating warm air throughout the home. If your evaporator coil is frozen, you should shut the AC off and switch the fan setting to “On.” This will help the coil to thaw out since the fan will continually blow warm air over the frozen coil. You must turn the AC off as soon as you suspect the coil is frozen or otherwise, you risk major damage occurring to the compressor motor if the system continues to run when frozen.

While waiting for the coil to thaw, you should check your air filter and replace it if it looks dirty, as a dirty air filter is the most common cause of a frozen evaporator coil. You should also make sure that all your supply and return air vents are open and not blocked by furniture or clogged with hair and debris as these issues can also limit how much warm air the blower can draw in.

If your AC freezes up again after you turn it back on, it is time to have a technician inspect the system. The system may be freezing because the refrigerant level is low due to a leak or for a variety of other reasons that only a trained technician will be able to diagnose and repair.

3. Control Board or Electrical Problems

Another possible reason your AC might be blowing warm air is that there is an issue preventing the AC condenser from running. However, there are times when a faulty or malfunctioning control board can fail to signal the blower to shut off when the condenser shuts off, which will lead to the system eventually blowing warm air.

An issue with the fan limit switch can also lead to the fan continuing to run after the condenser shuts off, and the solution to this problem is to have a technician reset the switch. The problem could also be related to an issue with a faulty contactor relay switch not signaling the condenser to run or some other electrical problem that prevents the condenser from starting.

If your AC is freezing up, blowing warm air, or has any other issues, you can count on Controlled Climate Services for help. We repair and service all models and types of central air conditioners as well as ductless ACs and heat pumps. We also specialize in HVAC installation, commercial refrigeration, and a full range of heating and indoor air quality services. Give us a call today to schedule an AC inspection or any other HVAC service in Kennesaw.

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