How to Troubleshoot a Vehicle’s Air Conditioner

AC Car Mechanic Inspecting Air Conditioning in Vehicle

What’s better than cranking up your AC during a long road trip in August? Powerful, cold air coming from your vents can make or break your trip. If you’re not getting the coldest and strongest air possible, you came to the right place.

I put together a list of reasons why your vehicle’s air conditioner might not be working. I also included some troubleshooting steps and solutions to fix your car’s AC. Follow along and see if you can find the culprit, fix it, and get back to having cold air blowing on you.

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How Your Vehicle’s AC Works

Knowing how to fix your car’s AC starts with understanding how it works. There are vents in the front of your vehicle that allow outside air to come inside your car. The air goes through a little science, and it’s shot out your air vents as cold air.

Cold air can’t affordably be generated like that. What happens is that your car actually takes the heat and humidity out of the incoming air, leaving you with cool air.

It works just like your home’s AC evaporator coil (an in-depth guide can be found here if you’re interested). Essentially, the coil uses refrigerant to suck the heat out of the passing air.

AC-diagram

The condenser is at the front usually near the radiator (3). The evaporator is usually located behind the dash (6). It looks similar to the condenser but is oftentimes smaller and the last important stop before you get cold air coming from your vents.

Refrigerant is a special liquid or gas that’s really good at absorbing energy and releasing the energy elsewhere. In our case, it’s absorbing hot energy from the air and transporting it away.

How does the refrigerant pump around your car’s AC system? The answer is – through a compressor. It pressurizes the refrigerant and pumps it away from the condenser after it’s used.

Finally, a blower fan will help pump that cooled air into your car through your vents. There are some flaps within your HVAC system that recirculate, direct and restrict airflow through your vehicle.

Common Reasons Why Your Vehicle’s Air Conditioner Isn’t Working – How To Troubleshoot Your A/C

Now that you understand how your AC system works, you can learn what’s causing your AC system NOT to work.

Let’s take a look at some of the more common reasons why your vehicle’s air conditioner isn’t working. Keep in mind that your car might be experiencing a number of these issues, so troubleshooting might take some time.

Refrigerant is Leaking (Low Level of Freon)

Remember that magical juice we were just talking about, refrigerant? Well, if you’re losing refrigerant anywhere in your system, it won’t be able to efficiently take the heat out of the incoming air.

Your car isn’t being constantly refilled with refrigerant. You’re relying on a reservoir that keeps circulating around.

Refrigerant is traveling through a series of hoses and tubes. If anything is cracked, not correctly sealed, or missing — refrigerant will escape and leak.

A/C refrigerant pressure hoses
A/C refrigerant pressure hoses

The reservoir you’re left with might still cool the air, but not to the level you’d like. Alternatively, it might not cool the air at all.

Troubleshooting: It can be tricky to find any refrigerant leaks. One way to go about this is by filling up the A/C system with a special dye that is visible with Ultra-Violet (UV) light and enough refrigerant to run the diagnostic.

Park the vehicle in a dark area, with the vehicle running and the A/C, turned on for a few minutes, you should see the special dye with a special UV flashlight to see exactly where the leak is coming from

Solution: Replace any seals, hoses, or components that are leaking refrigerant.

Broken Condenser

The condenser is the heart of this operation. It’s the part where all the magic happens. If the condenser is broken, hot air will come from your vents regardless of what temperature you set the HVAC to.

A condenser could break if road debris goes into the grill of your car. Your car’s condenser is a field of tubes that tightly wind their way upwards. It’s a rectangular piece that’s black and silver.

It’s located at the very front of your vehicle, immediately behind your car’s grill.

Troubleshooting: Take a look at your condenser. Look for punctures or any other types of damage. If there’s no visible damage, it could be an internal failure.

Solution: The only solution is a replacement. The part itself costs around $100.

Damaged A/C condenser
Damaged A/C condenser

Condenser or Evaporator is Clogged Up

Beyond a problem in the condenser, there could be a simple blockage on the exterior. This is a mechanical failure that is often easy to detect and correct.

It’s not uncommon for birds, leaves, and bags to cover the front of your grill or condenser as you drive along.

The evaporator that is directly behind the dash is also prone to failure. Inspecting it for any kind of failure would be something to keep in mind although due to its location, it might not be the first thing I’d try diagnosing in the A/C system.

Troubleshooting: Inspect the A/C condenser under the hood near the radiator at the front. Make sure there is no obstruction on either side of it and no immediate signs of an issue.

Inspecting the A/C evaporator might not be so simple, due to it being behind the dash, certain panel components will need to be removed before it can be diagnosed.

Solution: Remove any obstructions or replace the condenser or evaporator, then test your A/C again.

AC evaporator clogged up
AC evaporator clogged up

Cooling Fan is Faulty – A/C Fan, Fan Clutch, Fan Relay

The cooling fan is right behind the condenser. It gives the air a little boost and sends it through the rest of the HVAC system.

If a cooling fan isn’t working, it won’t create the correct amount of flow required. Air will navigate around the condenser without getting cooled down and it’ll work its way into your car. The result is a car that only emits hot air.

The A/C fan runs off a relay and sensor that tells the fans when to kick in and when to turn off. Any one of these components and wear out and fail.

Troubleshooting: This is another piece you’ll have to visually inspect. With your car running, see if the cooling fan is spinning. If it is, turn off your car and check for cracks or missing fins on the fan.

Also, A/C cooling fans run off an A/C relay. If that relay is at fault, the fans won’t kick in or will work intermittently. The A/C relay would typically be in the engine bay area along with other fuses.

Solution: I’d suggest taking your car to a mechanic for this fix. The only solution is a replacement.

A/C condenser cooling fans
A/C condenser cooling fans

General Electrical Issues – Wiring & Fuses

There’s also an opportunity that there’s an electrical disconnect somewhere in your vehicle. This could be a blown fuse, faulty resistor, or snapped wire somewhere.

Basically, if there’s no electrical signal to your vehicle’s AC, nothing’s going to happen.

Troubleshooting: If the AC doesn’t turn on at all, or the air is only warm, it could be an electrical issue. It’s also a viable candidate if you work through the other troubleshooting steps and don’t see anything physically wrong.

Inspect the wiring going to and from the A/C fan sensor to the fans and any other wiring related to the A/C.

Solution: Replace or repair whatever component is burnt, frayed, corroded, or simply not fully plugged in. You can use a fuse tester along with a multi-meter to inspect the fuses and relays for the A/C system.

Fuse box
Fuse box under the hood where the A/C relay and fuse are located

Bad Compressor

The compressor circulates the refrigerant and ensures there’s always fresh refrigerant to absorb incoming heat.

If the compressor doesn’t do its job, the refrigerant won’t actually cool the air that gets passed through.

AC-compressor
A/C Compressor will normally be at the front of the engine with the other belt-driven units.

Cabin Air Filter is Blocked

It’s also possible that the air doesn’t have a chance to come into your car. The cabin air filter is the vent on the exterior of your car that passes outside air inside.

A blocked cabin air filter works a lot like a clogged condenser. Since the air can’t pass through, your vents won’t get a strong flow inside your car.

What’s worse, if the cabin air filter is full of debris and clogged up, it can create a strain on the A/C system forcing your A/C compressor to work that much harder. This can also cause your “fan blower motor relay” to fail.

Troubleshooting: Check the air intake on your car for obstructions. One is located at the base of your windshield.

Solution: Clear any blockage and try your AC again.

Cabin-Air-Filter-Comparison-Dirty
Clogged vs. new air filter

Can You Troubleshoot and Fix Your Car’s AC on Your Own?

If you weren’t sure, a lot of these troubleshooting steps and solutions can be done on your own. In fact, a lot of them can be done with no car knowledge whatsoever.

Replacing components can be a little trickier. If you like wrenchin’, none of these projects are outside the realm of possibilities.

Conclusion

I hope that you found the reason why your car’s AC is acting up and corrected it thanks to this guide. Check out these other helpful articles on my blog. I also have a list of tools and accessories that you absolutely need for your car.

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Ernest Martynyuk

An automotive enthusiast who's been tinkering with vehicles since I was 15-years old. Repairing automotive electronics has been my main job for over a decade now and have a passion for everything technical regarding cars.

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