Why is my car AC blowing warm?

Summertime is the period where you’re banking on your car AC to keep you comfortable as you weave your way through traffic under the unforgiving sun. When your AC is functioning well you look forward to taking a ride in the car, but if it starts to malfunction, it can be a hellish experience because the temperature of a hot car can quickly hit 140 degrees or more.

The first sign that tells you something is wrong, is when you turn on the AC but all you feel is warm air blowing out of the air vents. What could be the problem?

There are several culprits that could be responsible for your AC problems, and today we’ll explain 5 reasons why your car AC is blowing hot air and how to fix it, so you can troubleshoot the unit by yourself and get it up and running, or to at least have an idea of what the problem is before taking it in for repairs.

The five most common car A/C issues are:

  • Leaking refrigerant
  • Electrical issues
  • Broken condenser
  • Faulty cooling fans
  • Bad compressor

Your AC Refrigerant Is Leaking

If your car AC is blowing hot air, it is very likely that the refrigerant in the unit is low. A refrigerant is a special kind of gas (but compressed to liquid) that gives the unit its cooling ability.

What it does is absorb heat from inside your car and radiate or give off the heat outside the vehicle thereby making the interior cooler than the temperature outside.

When the refrigerant circulating in the AC is low or leaking, the unit doesn’t have enough power to perform its cooling function – kind of like when someone has lost too much blood.

The problem in identifying where the leak is due to the nature of the refrigerant.

It is a liquid when inside the unit, but when there’s a fault in the pipeline that it flows through, it escapes as a gas which makes it tough to pinpoint the exact location where it is leaking from.

The most common place where refrigerant can leak from are joints and connection hoses in the unit.

It can leak anywhere in the evaporator, the condenser, the compressor, or in the copper coil.

Like I already mentioned, the liquid refrigerant becomes gas when it leaks, so you won’t see the normal tell-tale puddle of water under the car, you’ll possibly see an oily substance collect around the area that’s leaking.

You or preferably a technician can use a sealant to plug this leak.

I recommend getting a professional air conditioning technician to fix the problem, they’ll inject a dye into the unit to trace and fix all leaks.

Problems With The Electrical System

Your car’s electrical is a jungle of cables, fuses, relays, and switches.

When everything is in sync and working as they should, the electrical system delivers the needed power to run the AC unit, providing you cool air and comfort on demand.

If one of these components in the electrical system fails due to a defect in the system, age, or a power surge. The system is designed to shut power to certain components to prevent further damage or unsafe conditions for the user.

While this setup and protective features help prevent dangerous fires from growing in the electrical system, it also means that something as simple as a blown fuse could cause your AC to stop working.

You’ll need to inspect all the wires entering and exiting the AC to see if any wires are broken or frayed. You should also trace them all the way to the fuse box to see if there’s a broken fuse. If notice any wire that looks melted or burnt, then you’ll need to replace them and possibly change a fuse.

I have to warn you, it’s quite difficult to locate or isolate the cause of an electrical problem without the proper test instruments and the necessary experience to diagnose such problems.

If you’re unable to detect any electrical issue in the system, then it’s time to take your vehicle to the garage for further diagnosis.

The AC Condenser Is Bad

The condenser is the part of the AC unit that’s responsible for radiating or dissipating the heat from the liquid refrigerant coming from the compressor.

When this component works as expected, it allows the liquid refrigerant to cool down a bit so it can return to a gaseous state again as it flows back through the rest of the unit.

On and on, the cycle continues.

When the process fails, that’s when you get punched in the face by a fistful of hot air.

It looks a lot like the engine radiator, only a bit smaller. It is located at the front of the car, between the radiator and the grate.

You’ll spot a pair of cooling fans mounted in front of the condenser to help move the heat away from the unit.

When the ventilation holes on condenser are blocked by the accumulation of dirt and road debris, air won’t flow freely over the copper coil, thereby forcing the component to retain some of the heat and the result is weak cooling or hot air.

If on inspection the condenser doesn’t look blocked or clogged, you should ensure that the copper pipes look okay.

If there’s an area on the pipe that looks compressed, then it might be blocking the free-flow of refrigerant through the unit.

This might result from road projectile smashing into the pipe or an accident that caused a bump in your fender or bumper.

Bad Cooling Fans

Recall that I did mention that the condenser has a pair of cooling fans mounted in front of it. The compressor and the fan(s) work hand-in-hand to get rid of the heat, but if the fan isn’t blowing at the optimum speed needed to get rid of the eat, then the partially cooled refrigerant will leave the condenser bad into the unit.

A visual inspection will tell you if the fan is in good shape and is working properly.

They aren’t the sturdiest component on a vehicle, so consider checking them for cracks that may have formed from impact with road debris.

Other common issues that might cause the fan to operate below-par are fuses and electrical issues. You might have to get a replacement fan in some cases or the help of a professional to address the issue.

The Compressor Has Issues

The compressor is the heart of the AC and its job is to keep the refrigerant moving through the unit at all times.

If it is faulty, the refrigerant cannot move through the system and you will never get anything close to cool air.

Compressors rarely develop issues when you’re using them.

The most common cause of compressor failure is inactivity – try to imagine a component that wants to work all the time or it fails.

An extended period of inactivity tends to shock the component when you finally use it.

This extended period of inactivity perfectly coincides with winter when you don’t need the AC running, but you there’s something you can do to keep it active.

We recommend running AC on full speed for 10-15 minutes every two to three weeks irrespective of the outside temperature.

You could run it in the winter with the fan or air vent block, or maybe leave it on for some time before you lock the car and retire for the night.

Other Possible Issues

Your Compressor Clutch Is Bad

Another issue that might be affecting the performance of the compressor is the compressor clutch. What is a compressor clutch? What does it do?

A car AC compressor clutch is the part of the compressor that connects and disconnects the compressor from the engine’s mechanical power.

Simply put, it connects the compressor to the engine so it can harness the rotational motion that the engine produces to make cooling possible.

Unlike the transmission clutch that can transmit partial power, the AC compressor is either on (full power from the engine) or off (no power from the engine).

Since it cycles between on and off continuously, it is also subject to wear and tear. A slipping AC compressor clutch means there’s an incorrect air gap, shorted clutch coil, or just aging.

The compressor clutch won’t engage if:

  • The clutch fuse is blown
  • The clutch relay is faulty
  • System pressure is too low, which means the refrigerant is leaking.
  • System pressure is too high, which means there’s a blockage somewhere.
  • The thermal fuse or flow control valve isn’t working or is blown.
  • Improper clutch plate air gap

You’ll need the service of a professional car AC technician to figure out which of these is the issue.

A Faulty Expansion Valve

Whenever your car AC continuously switches back and forth between hot and cold, chances are that the expansion valve is faulty.

The job of the expansion valve is to distribute a certain quantity of refrigerant to the evaporator.

In a situation where the valve is clogged, the flow of refrigerant could be obstructed or without restriction.

If the refrigerant is restricted even slightly it can cause the expansion valve to get so cold that frost or ice collects on the exterior of the hardware.

The result? Your car AC blows warm on the inside but cold on the expansion valve.

If you notice a poodle or drops of fluid under the car, then it’s very likely from a bad expansion valve (assuming your radiator isn’t faulty).

This could help your mechanic to diagnose and fix the problem.

What Does This Mean For You?

This list of car AC problems is by no means a comprehensive list of all the different things that could be responsible for your AC blowing hot air.

Most of them are fixable and very rarely will you need to overhaul your vehicle’s air conditioning system.

If you have the skills and experience to fix any of these issues yourself, then you should get the best replacement part you can find (if replacements are necessary) so you don’t have to do it twice.

Your friendly technicians at All Phase Auto Repair can diagnose and repair any problem with your AC system.

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