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AC not blowing cold air: step by step DIY repair guide

Last updated: Nov. 1, 2022, 9:31 a.m.

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Is your air conditioner running but not blowing cold air? Good news, this guide was written just for you. In it, you’ll find seven DIY ways to troubleshoot and fix the most common AC issues. If you’ll take your time and methodically work through each of them, there’s a good chance your air conditioner will be working again today.

NOTE: None of the below are super technical or difficult, but please don’t do them unless you feel comfortable working around your AC system. It is a serious piece of machinery and you can get hurt if you aren’t careful.

Your AC is running but not cooling

Step 1. Confirm both parts of your AC system are turned on at the breaker panel

It’s hard for your AC to work when it’s turned off. So quickly confirm that a third party or mischievous child hasn’t left your AC circuit breakers off. You should have two switches: one is usually labeled “AC” and the other “furnace” (also look for any switches labeled HVAC, heat pump, or air handler). Once you find them, confirm they are both in the on position. If they are in the off position, flip them and your AC should start working again. If they are in the middle position, your breaker has tripped and you have an electrical issue. Please call an HVAC technician.

Step 2. Check that your fan is set to “Auto” and not “On”

If your AC blows cool air sometimes and warm air other times, your thermostat fan setting may be set to “On”. That means your fan runs all the time — including the times your air isn’t being cooled. Just flip the switch to “Auto” and your warm air issues will be gone.

Step 3. Change your filters

Dirty filters make it harder for your system to work. If they get dirty enough, they can cause your system to freeze up or even shut down completely. That’s why it’s so important to change your filters at least every three months.

If you’ve never done it before, changing your filters is really easy. They are usually behind a grill that looks like the below:

return air vent

Once you locate your grill, open it up and carefully pull the filter out. On the side of the filter, you should see some measurements. Write those down and then go to your local Walmart or home improvement store and buy a replacement. Once you get home, install the new filter with the arrow pointing away from you (in the direction of the air flow).

Note: If you can’t find a grill like the above, your filter may be next to your indoor HVAC unit (furnace or air handler). Typically, that is in the attic or a closet. It may also be in a crawlspace if you live in an older home.

If your filter was dirty, you may have found the source of your AC issues. To confirm, put your AC on the fan only setting for a couple hours. This will allow your AC to thaw out if it has frozen up due to a lack of air flow caused by a dirty filter. Then, turn your AC back on and set it to your desired temperature. If the filter was the problem, your system should start working again.

Step 4. Clean your AC coils

Dirty AC coils can cause all sorts of issues for your AC system. That’s why people typically have them cleaned once or twice a year. If it’s been a while since your last cleaning, this may be why your AC is not working.

The good news is that you can DIY clean both your condenser coil (part of your outdoor unit) and evaporator coil (part of your indoor unit). It takes some time and you might get a little messy, but you can definitely do it. If interested, you can follow our in-depth guide on how to clean your AC coils here.

Other common AC issues

Outside AC unit not turning on

If your AC compressor (technically the entire unit is called a condenser) is not turning on, you either have a refrigerant issue or an electrical issue. There’s not much you can legally do if it’s on the refrigerant side since refrigerant is federally regulated, but there are a couple things you can do if the issue is on the electrical side.

One, confirm that you are getting 24 volts from the thermostat to your AC unit. You may have a loose wire at the thermostat or a break in the wire between the thermostat and condenser (weed eaters are notorious for cutting AC wires). Either will cause your HVAC system to not work.

To rule this out, grab a multimeter and follow the Youtube video here.

NOTE: Only follow the above video if you are experienced working with electricity as one wrong move can hurt or even kill you.

If everything above checked out, you may have a bad contactor. Like the above step, changing a contactor is dangerous and should only be attempted if you have extensive experience with electricity. If that’s the case, you can follow the Youtube video here to change yours.

AC fan not working

There are a few reasons why your AC fan may not be working, but the vast majority of the time it boils down to one of two things: either your capacitor is dead or your fan motor is dead.

Replacing either requires a working knowledge of electricity. If you don’t have electrical experience, I would strongly recommend you call an HVAC technician. HVAC systems are dangerous, and if you don’t know what you are doing, you can get hurt or even killed.

That said, if you know how to safely work around electricity, you can follow this video here on how to replace an AC capacitor and this video here on how to replace an AC fan motor.

AC not running

If your AC system isn’t coming on at all, you may have a clogged drain line. If your thermostat is blank or has lost power, there’s a very good chance that’s the issue.

Good news: you can clean a drain line out using basic tools available in most any home. Learn how by following our DIY guide here.

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