Here's What to Do When Your AC Unit Is Blowing Warm Air

Before you schedule a service visit, you may want to try and fix your AC unit yourself. Here are some common AC problems that you can fix yourself. And if you run into trouble you can always call an HVAC professional.

Check Your Thermostat

Before you panic about your AC not working, make sure the thermostat is set properly. You’d be surprised how often this is the real issue, especially at the beginning of the season, or among homeowners who’ve never had central air before. Set the thermostat to “cool” and the fan system to “auto.”

Your thermostat should display your home’s current indoor temperature. Make sure you set the temperature to at least five degrees below that temp. If all is working correctly, this should prompt your AC unit to start blowing cool air.

Change Your Air Filter

When was the last time you changed your air filter? If it’s been longer than six months, or one to three months if you have pets, then it’s time to change it. 

Your HVAC system’s air filters keep dirt and debris from getting into your HVAC system, including the AC and furnace. But over time, the filter can get clogged up with dust, debris, and pet hair, and that can stop air from flowing freely into your A/C unit. As a result, your AC might not be able to work effectively. Change your air filter, and set an alert on your phone to remind you to change it again in one to six months. Change it more frequently if someone in your household has allergies or asthma, or if you have pets. Change it less frequently if you're a pet-free household without breathing issues.

Clean The Outdoor Unit

Just as a dirty filter can cripple your air conditioning unit’s ability to cool your home, dirt and debris on the outdoor portion of your AC unit can do the same. This outdoor unit is called the condenser, and it contains cooling tubes, fins, and a blower fan. Behind the unit, on the exterior wall of your home, you should find a box containing an electrical shutoff. 

Before cleaning your condenser unit, you should open up that box and either flip the switch inside to “off,” or pull out the block shutoff. If you can’t figure it out, just go inside and turn off your AC unit at the breaker box. Either way, you need to shut off power to the unit.

Now, get out your shop vac, put on the soft-bristle brush attachment, and vacuum the outside of the fins to remove any debris. Pull up any weeds or grass growing within two feet of the unit. If you see crushed or bent fins on the outside of the unit, you can gently straighten them with a butter knife, but be careful -- and don’t insert the knife blade more than half an inch into the unit.

Once you’ve finished cleaning the outside of the air conditioning unit, unscrew the top of the unit and gently lift out the fan. Don’t put any strain on the electrical wiring as you do so. Wipe off the interior of the unit with a damp cloth. Finally, use moderate water pressure from a garden hose to spray off the fins from the inside. Replace the fan, screw the top back on, and restore power to the unit.