AC Not Blowing Cold Air? Here Are the Top 8 Causes

Did your AC stop blowing out cold air?

It could be due to a multitude of reasons—anything from a broken thermostat to a dirty coil.

In this article, I’ll go over the top 8 reasons why your home’s AC might not blow cold. I’ll also go over how to fix an AC that’s not blowing cold.

1. Low refrigerant charge

If your AC has a low refrigerant charge, then your AC will not blow cold. A low refrigerant charge happens when there is a refrigerant leak in your AC.

If your AC’s refrigerant is low or has a leak, then your AC will suffer from reduced cooling performance.

Worse yet, your AC system will use more energy to cool your home. Your AC compressor may also become damaged as a result of low refrigerant charge.

So how do you know when your AC has a low refrigerant charge?

One of the easiest ways to tell is if your AC line freezes up.

If you see ice or condensation on the line connecting to your condensing unit, that’s a telltale sign that your AC is low on refrigerant.

Refrigerant doesn’t get used up when you run your AC. So if your AC has a low refrigerant charge, then it most likely has a refrigerant leak.

If your AC has a low refrigerant charge or refrigerant leak, then you’ll need to get an HVAC professional to repair it.

2. Dirty condenser coil

If your AC’s condenser coil is dirty, your AC will not blow cold because your AC cannot reject heat from your home.

The condenser coil is the coil on the AC unit outside your home. The purpose of the condenser coil is to move heat from the refrigerant to the air outside your home.

If your AC’s condenser coil gets excessively dirty, then your AC won’t be able to remove heat from your home and your AC won’t blow cold.

Fortunately, cleaning a condenser coil isn’t a difficult task—in most situations, all you need to do is spray it down with your water hose to remove dirt and debris.

However, if your condenser coil is clogged with excessive grime or debris, then you may need to use a cleaning solution to aid in cleaning the coil.

3. The thermostat is not set correctly

If your thermostat is not set correctly, then your AC won’t blow cold when your home gets hot.

That’s why it’s important to check if your thermostat is calling for cooling in the first place.

I recommend setting your temperature setpoint as low as it can go. Next, check if your cooling kicks on.

You should hear an audible “click” from the relay in your thermostat when it calls for cooling.

Another thing to check is the mode setting on your thermostat—especially if you have a split AC.

Thermostats usually have a few different modes—such as auto, heat, fan-only, etc. Make sure that your AC is in cooling mode and not a different mode such as fan-only.

If you suspect that your thermostat is bad, you can try bypassing the thermostat.

To bypass your AC’s thermostat, wire in a jumper at your AC unit’s control board (see the picture below).

If your AC starts blowing cold when you bypass your thermostat, then you know that something is wrong with your thermostat or the thermostat’s wiring.

Wire a jumper between the R and Y terminals to override cooling in your AC
Wire a jumper between the R and Y terminals to bypass your thermostat and override cooling in your AC

4. Clogged condensate drain pipe

If your AC’s condensate drain pipe is clogged, then your AC may disable its cooling.

Why does that happen?

Some ACs have a float switch installed in them. The float switch is used to detect the presence of excessive water due to a condensate backup.

If the AC’s condensate drain pipe gets clogged, the float swill will activate and shut off your AC’s cooling.

Depending on how the float switch is wired, the AC may still blow warm air around your home—or it may turn your AC off completely.

If your AC’s condensate drain pipe is clogged, you’ll need to unclog it before your AC will blow cold again.

For more information about how to unclog your AC’s condensate drain pipe, check out my article below:

5. Dirty air filter

If your air filter is dirty, then your AC will have trouble cooling your home.

A severely clogged air filter may even prevent your AC from blowing cold.

Why does that happen?

It’s due to one reason: A frozen evaporator coil.

When your AC’s air filter gets clogged, it will restrict airflow through your system.

If the airflow through your AC system gets too low, the evaporator coil will start to freeze up.

I’ll go into more detail below about what happens when your AC’s evaporator coil is frozen.

6. Frozen evaporator coil

If your AC’s evaporator coil is frozen, then your AC won’t blow cold. A frozen evaporator coil will inhibit the cooling capacity of your AC, preventing your AC from cooling your home.

When ice forms on your AC’s evaporator coil, the air flowing through your AC system will have trouble getting cold.

The reduced heat transfer from the evaporator coil will result in your AC not blowing cold.

So what do you do if your AC’s evaporator coil is frozen?

The first thing that you should do is defrost the coil.

After the coil is free of ice, you’ll need to figure out why the coil got frozen in the first place—it’s usually due to an airflow or refrigerant issue.

For more information about what to do when your AC’s evaporator coil is frozen, check out my article below:

7. The compressor capacitor is bad

If your AC’s capacitor is bad, then its compressor won’t turn on and your AC won’t blow cold.

The capacitor is responsible for giving your AC’s compressor the initial “jolt” of electricity to turn on.

If your AC’s compressor capacitor goes bad, then your AC will have all sorts of issues—and it won’t blow cold.

So how can you tell if your compressor’s capacitor has gone bad?

Two common symptoms of a bad compressor capacitor are a blown fuse or tripped breaker.

If your AC unit blows a fuse or trips a breaker, then there’s a good chance that the capacitor is bad.

The most surefire way to figure out if your AC’s capacitor has gone bad is to test the capacitor using a multimeter.

For more information about AC capacitors, bad capacitor symptoms, and testing capacitors, check out my article below:

8. The condenser contactor is bad

If your AC condenser’s contactor is bad, then the AC unit outside won’t turn on. This prevents your AC from blowing cold.

So why does a bad contactor prevent your AC from blowing cold?

The contactor is the “switch” that turns on your AC unit outside.

The contactor is controlled by your thermostat—when the thermostat calls for cooling, it activates the contactor. The contactor then powers on the compressor and condenser fan in your AC unit.

If the contactor stops working, then your AC unit outside won’t turn on, and your AC won’t blow cold.

Another issue that a contactor can have is pitting on its metal contacts.

Over time, the electrical arc that occurs when the contactor turns on will cause the metal contacts in the contactor to get pitted.

If the contacts get too pitted, the contactor can’t make a connection and won’t transfer electricity.

If your AC’s contactor stops working or gets pitted, then you’ll need to replace the contactor before your AC will work again.

Hi, my name is Trey Lewis and I’m the founder and chief editor at HVAC Training Shop. My goal for this website is to help homeowners troubleshoot and maintain their home’s HVAC systems. Whether it’s changing an air filter, troubleshooting a blower motor, or just buying a new humidifier, I want to make sure that you’re covered.

Leave a Comment