Why Is My AC Blowing Hot Air? How to fix? [With Pictures]

You’ve been sunbathing in your backyard for an hour, and once the timer finally beeps, you’re absolutely sizzling. You scurry across the patio stones, go inside, and close the door behind you. But the house is warm! You walk to a nearby AC supply vent only and feel a jet of warmth. Somehow, your AC is blowing hot air. If this sounds familiar, you’re not alone.

Every summer, Americans across every state and city are faced with the same problem. We’ll tell you why. And if your AC will not turn on at all, learn what to do in our blog on that subject as well.

How Does An AC Work?

Firstly, let’s go through the basics:

Your AC system is not creating cool air.

Instead, a fan pulls warm indoor air through a filter and over the evaporator coil. The coil is full of refrigerant – a special chemical – and when the warm air is pushed over it, heat is absorbed by the refrigerant in the cold coil. The air, which is now cool, is blown back into the warm areas of the house.

Now, if the air being blown back into the house is warm, the coil, for some reason, is not extracting the warmth from the air. (We’ll expand on that later).

Once the refrigerant is hot, it is turned into gas and passed through the compressor. As the name indicates, this is where the hot gas is compressed into an even hotter vapor.

The third step happens within the condenser unit – the heat of the hotter vapor, sent over by the compressor, is discharged outside, returning the refrigerant in the coil into a cool liquid and restarting the cycle.

At this point, you might be thinking "this sounds complex. How could I possibly locate the problem with my AC?"

Believe it or not, with our help, you’ve got a chance. Keep in mind, however, that you may not be able to, in which case you’ll need to call AC experts like those here in SuperTech HVAC (if you lived in Maryland).

Let’s go through your checklist.

Seven Possible Reasons Why Your AC Is Blowing Hot Air 

The Thermostat Could Be The Culprit For Your AC Blowing Hot Air.

This first check on our list is simple enough – make sure your thermostat is set to cool (you’d be surprised how often it isn’t). Next, check that the fan is set to AUTO, not ON. This way, the fan only rotates when there’s cool air ready to be blown into your home. And finally, check that the temperature is at the proper desired level!

If none of that works, there’s likely a mechanical issue along your air conditioner’s closed loop system. Check out our blog discussing why your thermostat isn't working if you want to learn more.

Is The AC Coil Frozen?

Because of the chemical properties of the refrigerant, when heat is not absorbed into the coil for a certain amount of time, it freezes.

So, what prevents the presence of hot air around the coil?

Airflow is somehow being cutoff, which can mean one of several different things:

• Dirty air filter. Dirt and debris are blocking warm air from entering the return vent. OR a household object - like a sofa or blanket - is in the vent’s way and blocking air flow.
• In a less common scenario, your air duct has collapsed due to wear and tear, bad installation, or pests, and air from the return vent cannot reach the coil.
• Dirty evaporator coil. The evaporator coil is covered in a layer of grime and air cannot pass through it. If dirt has made its way into this area, you may have a defective filter or cracks/fissures in your air ducts.

Additionally, your indoor air may start to smell musty if you have a frozen coil due to the development of bio-growth.

If your air conditioning system seems intact and clean, your system might be low on refrigerant, leading to a frozen evaporator coil.

So, Your AC Blowing Warm Air Could Be Due To A Refrigerant Leak.

We explained how the refrigerant, when put under pressure, gets hotter. The same is true of the inverse. With low refrigerant levels, the chemical liquid in the coil expands, cooling it until it freezes.

Because your AC is a closed-loop system, if your refrigerant is low, it is escaping the refrigerant line through a leak. And once the coil has frozen over, your AC cannot extract the warmth from your home’s air. It is simply sent back un-conditioned.

Don’t try fixing the freon leak yourself. Call an HVAC technician to do a “leak search” to locate it, repair the hole, and add the correct refrigerant into the evaporator coil to normalize the levels. For those of you living in Maryland, you can get AC help here.

Your AC not blowing cold air as a result of dirty condenser coil.

Your outdoor unit houses the other end of the coil, where the refrigerant arrives as a hot vapor and is released into the outdoor air.

To learn more about this subject, check out our refrigerant leak blog.

Your AC Not Blowing Cold Air As A Result Of Dirty Condenser Coil.

Because the box that covers the coil needs to transfer the heat outside, it is vented. Being exposed to the extremes in weather, it can also sustain considerable damage. Dirt, debris, critters, and even grass can find its way onto the exposed coil through the vents, or holes and cracks, and interfere with normal operation.

If you don’t want your AC blowing hot air, it’s important to keep the area around the condenser box clear of obstruction. Air is constantly flowing in and out, so the condenser needs at least two feet of “breathing room.” Without it, the coil’s cooling capabilities will be hindered.

Your Compressor Might Have Failed, So Your Air Conditioner Is Blowing Hot Air.

Like a heart, the compressor circulates the refrigerant around your HVAC system. In every cycle, low pressure gas becomes high pressure gas at this stage.

Being such an important part of your central air conditioner, the compressor requires the most electricity to run. An aging compressor pulls more and more electricity every year. Eventually, the aged compressor could trip your breaker by pulling too much, leading to your air conditioner blowing warm air.

Age can also lead to contaminants settling in the closed loop system – things like rust and other metal particles can block the refrigerant from its normal function.

Your worst-case scenario is a grounded compressor. This means some wiring in the motor has been severed, causing a short. If this is the case, you’ll have to get the compressor or entire outside AC unit replaced.

Compressor issues can be difficult to assess. When in doubt, the simplest thing to do is call an expert – like the team at SuperTech HVAC – for help.

Our blog about AC compressor failure offers more detail about reasons for your compressor having failed.

Or Is It Your Condenser Fan?

This fan in your outdoor unit sends the heat from the coil outside. Without it spinning, your condenser will overheat and get shut down by a safety mechanism, usually a high pressure switch, to prevent AC system damage.

When this happens, your coil is no longer capable of extracting the warm air from your house.

In other words, your condenser fan could easily be responsible for your AC not blowing cold air!

The likeliest scenario is a burnt-out fan motor that has resulted from general wear and tear. Sometimes, the simplest fix is a whole new outdoor unit (yes, we can help with that).

The fan could also be damaged. Things like rust, damaged bearings, and debris can halt rotation.

Keep in mind: if your fan isn’t getting power, it can’t turn. To learn more about the causes of your AC fans not working, check out our blog about them.

Loss Of Power To Outdoor Unit Could Be The Cause Of Your Air Conditioner Blowing Warm Air.

With a dated electrical system and outdoor AC unit, you risk blowing a fuse on a hot day. Why? Well, as we mentioned earlier, an older AC unit will struggle to meet your cooling needs and require too much power to accomplish its goal. The circuit becomes overloaded, and if the fuse overheats (there are other possible causes for this), the circuit will be disabled.

Modern AC setups incorporate a circuit panel instead of a fuse that “trips” when the circuit is overexerted. If this has happened, you can simply flip the switch back on.

Make sure to monitor the situation, and if it happens again, there’s an internal issue you need to fix.

But don’t try to find the bad wiring yourself! Instead, call for help.

What you CAN do yourself is check that your AC’s disconnect box hasn’t been accidentally switched off. It is located near the compressor (outside) and allows you to manually cut the power to your AC.

Here's How To Troubleshoot The Problem Of AC Blowing Hot Air Yourself Before You Call Us

• If you notice the entire outdoor unit not working – not just the fan or coil – check whether the breaker has tripped. If so, try resetting it. Your circuit breaker is usually a grayish panel with a door located in a low-traffic area in your house, like your basement or garage. 

• You can also check and re-set your AC’s disconnect box (see section above).
• If your coil has frozen, there are things you can do before calling the pros:
• Turn the AC off and fan on to melt the ice.

• Make sure your vents are open and your filters aren’t dirty (replace your filters if they are).

• Check that nothing is blocking air flow into your return and supply vents (furniture is most commonly the culprit).

The next and final step is calling SuperTech HVAC for air conditioner repair; or, if outside Maryland, your local HVAC technician.

How Do I Prevent My AC From Blowing Warm Air In The Future?

The easiest and most essential thing you can do to maintain your air conditioning unit in good shape is to change the clogged air filter! Set reminders every quarter and keep filter backups for an easy swap.

It’s also a good idea to get professional maintenance done in the spring before your AC’s workload ramps up for the summer (especially if your AC system is old).

A good HVAC pro will check your:

• Thermostat
• Fuse box
• Refrigerant levels
• Compressor

Additionally, they will clean your AC's coil to prevent it from freezing, clear your AC's drain line to keep it from leaking water, and check for any other AC repairs. 

And much more! Explore all the ways an HVAC professional reduces the risk of your air conditioner blowing warm air in our blog about AC maintenance.

Remember,

Some TLC is needed to keep your air conditioner from blowing hot air. By signing up for a maintenance plan with Baltimore's top AC contractor, you can avoid expensive air conditioning problems.

It’s never a bad idea to call and ask for help in AC maintenance, AC repair, or AC installation. We always tell our clients to take every necessary precaution, even if it means asking us a silly question!

If you live in Maryland and have any questions (silly ones included), call us today or schedule online to speak with one of our experts so we can help you fix the problem with your AC blowing hot air!