Car AC Compressor Won’t Turn On? 8 Reasons and Solutions

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Car air conditioning

It’s really frustrating when you flip your car’s AC on and you still get pummeled with hot air. During a hot summer day in the South, this is enough to drive you insane.

If the AC compressor doesn’t turn on, the most common culprit by far is low AC refrigerant. If there is a leak, no matter how small, it’ll eventually cause a non-working AC system. Another possible issue is a blown fuse and/or relay. Your owner’s manual should be able to tell you where those are located. Poor grounding, frayed wiring, bad clutch coil, and defective AC pressure sensor switch can also be an issue although less common.

The good news? Hot air blowing from your vents isn’t a death sentence for your car. It could be the AC compressor not turning on. In this guide, we’ll give you 8 reasons why your car’s AC compressor isn’t turning on along with some solutions to each problem.

What Is an AC Compressor?

The compressor is just one part of your car’s HVAC system. A lot of people don’t really think about how that cold air gets cranked out of your car’s air ducts even when it’s 100 degrees outside.

It takes a little bit of magic and a whole bunch of science.

Your car sucks in air from outside as you drive along. The air goes through a process that takes all the heat and humidity out of it. The result? Cold air coming from your vents.

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

One of the big culprits is your AC compressor. There’s a gas vapor called refrigerant that does all the magic of taking the heat out of the air.

The compressor circulates this refrigerant around. Once the refrigerant sucked up its fair share of heat, the compressor moves it out of the way so “fresh refrigerant” can take its place.

If the compressor doesn’t do this, the air won’t be sufficiently cooled as it passes through your HVAC system and out of your vents.

Automobile air cooling system.
The air cooling system in the car cabin is primarily used to remove heat from the cabin, using the compressor and clutch plate device to working start.

8 Reasons Why Your Car AC Compressor Won’t Turn On (and Solutions)

There are a number of reasons why your AC compressor might not be working. Each reason’s solution is a little different. Let’s take some time and explain all 8 reasons why your car’s air conditioning compressor won’t turn on.

1. Low Refrigerant in the AC System

This is by far the most common issue as to why your AC is not working. Low amounts of AC freon refrigerant will be detected by the AC pressure sensor switch, causing the AC not to kick in.

The most common refrigerant used today is the R134a refrigerant. There are two pressure states that need to be checked. As seen in the pic below the low-pressure is represented by the blue whereas the high-pressure side is the red one.

When using AC manifold gauges to check for good pressure, check both high and low. On the low side, there should be around 30-40 PSI at 75 degrees ambient temperature outside. If it’s on the low side, this may be an indication that there is a slow leak.

On the high-pressure side, the PSI should be twice the ambient temperature. So for example, at 75 degrees outside, the high pressure should be between 150-170 PSI approximately.

Solution: After testing the AC for the amount of PSI in both low and high-pressure lines, re-fill the AC and monitor the gauges carefully. Some AC refrigerants already come with the gauges built-in.

AC freon refrigerant refill
Re-filling AC freon refrigerant

If you suspect there is a leak when re-filling the AC refrigerant, a dye can be used so that next time it stops working, the dye will be visible when you check it in the dark with a UV light.

Any leaks will glow in the dark (greenish-glow). I would recommend starting at the A/C compressor and going along the A/C lines inspecting all areas carefully.

2. A Faulty Car AC Pressure Sensor Switch

When you click the dial on your center console to “cold” nothing happens, it could be thanks to a busted temperature control switch.

This switch toggles your HVAC system from hot to cold. If the switch isn’t working, then your car’s HVAC will be stuck on one of the two settings.

AC pressure sensor switch
AC pressure sensor switch

In your case, it’s stuck on the heat setting. Your compressor might be fine, it’s just not getting the signal to get things chilly.

The only problem is that it’s not easy to test this control switch. Your best bet is to try some other things on this list and if it still doesn’t work, then replace this temperature control switch.

Solution: Replace the temperature control switch.

Relay or Fuse Problem

Capacitors and relays are little electronics that are built into the wiring around your car. Without getting into the electrical intricacies, we should tell you that these pieces are imperative.

Car fuse box closeup. Multiple rows of different fuses, one connector and part of a relay visible.
Car fuse box closeup. Multiple rows of different fuses & relays

If a relay or capacitor has a problem, the full voltage won’t make its way through the full journey. All of the voltage needs to make it to your compressor or else it won’t run.

Solution: Inspect the capacitor and fuses for the A/C, replace them if they look worn or damaged.

Compressor is Dead

The simple fact is that sometimes the compressor is just dead. A component inside of it might have broken, leaving it powerless.

detail of the engine  fragment include ac compressor belt and pulley.
Inside the engine bay – A/C compressor mounted to the engine with belt installed

Once the compressor is dead, the only solution is to completely replace it. This is something that you can do on your own so you don’t have to take it to a mechanic. It might be a couple of hundred bucks in parts if you choose to tackle this project.

Solution: Replace the compressor.

It’s Not Getting Power

The compressor needs to get voltage before it can turn on. If this wasn’t the case, your AC would be blowing even when the car was turned off.

Inspecting the car battery
Inspecting the car battery to ensure it’s getting at least 12v

That means that if the vehicle has low voltage, it can affect the electronic modules that affect the air conditioning system. Once the vehicle is running, the alternator will provide constant voltage, but there could still be some error codes.

Solution: Troubleshoot your battery. If it’s getting below 12 volts, it could be a faulty battery. Try jumping your car, or check if the battery needs to be replaced.

Wiring Issue

Yet another electrical issue that can arise is improper wiring. This doesn’t mean that the compressor manufacturer crossed some wires, it means that something went wrong along the way.

If your compressor never worked, then it could mean that the internal wires weren’t installed correctly. If you just recently installed the compressor yourself, make sure you ran the wires correctly.

Large wide cable with multicolored red and green wires and conne
Visually inspect the A/C wiring going to and from the A/C components (Fan clutch, compressor, fuse/relay) in the engine bay to the other side of the firewall where the ECU/BCM and climate control are. Sometimes wiring can get corroded, frayed, or be completely severed.

If this problem started happening randomly, you might be able to thank mice. They are known to chew through wires to sharpen their teeth. You’re left with disconnected components all over the place.

Solution: Check for damage to wiring and ensure all connections are tight.

Compressor Clutch Isn’t Engaging

The compressor shaft will rotate when it’s turned on. There’s a little clutch that then gets pushed against the shaft and engages. Once the clutch is engaged, the air will start cooling down.

If the clutch doesn’t engage, then the compressor will just freely spin with no reaction.

AC-compressor-clutch-highlighted

There’s an easy way to troubleshoot this. Turn your car’s HVAC setting to “heat” to blow hot air. Pop the hood of your car and locate the compressor. You should notice the disk on the pulley side of your compressor is not moving at all. This is the clutch and it should be disengaged when your car is running the “heat” mode.

Get in the car and turn it to AC and go back to the front of your car. Check to see if the clutch is moving now.

Solution: Check the connections on the clutch and replace the clutch if there’s mechanical damage to it.

Rusted Clutch Plate

Let’s start by saying that rust on certain parts of your clutch plate isn’t going to cause your compressor to break. It’s actually the byproduct of a compressor that has seen better days.

Rust on the outer ring of the clutch, however, could be the culprit. In either case, if you spot rust, it could be an indicator that your compressor died from old age.

Solution: Replace the clutch plate and potentially replace the compressor, too.

Prevent a Dead AC Compressor in the Future

As you can see, there’s a lot of troubleshooting that goes into fixing an AC compressor that won’t turn on. If you want to skip this laborious troubleshooting, you should know how to prevent this problem.

The biggest means of prevention is maintenance. You might want to get an AC tune-up from a car shop every spring so you can get ahead of the problem.

Mechanic with manometer inspecting auto vehicle air-condition co
Mechanic inspecting the vehicle’s air-conditioning compressor with a manometer.

Besides that, it’s a good idea to run the AC for 10-15 minutes once a month, regardless of how cold it is outside.

If you spend a little time and money today on maintenance, you can save a lot of money tomorrow. This is one of many ways to ensure your car lasts forever.

Conclusion

We hope that you find the root cause of your AC compressor not turning on. Our 8 reasons and solutions should help you narrow it down and troubleshoot your way through this issue. For more car maintenance tips, explore our blog. Make sure you have the right accessories and tools to make things easier.

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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.

22 thoughts on “Car AC Compressor Won’t Turn On? 8 Reasons and Solutions”

  1. Which of the following components is most likely to cause the AC device to malfunction? The reasons you have mentioned here happen suddenly with car AC and show signs of the machine breaking down. I like your suggestion to consider the warranty coverage when choosing a new system. My brother wants to have a new air conditioning system installed in his car. The info you shared here should come in handy when he starts talking with an AC service about choosing a system!

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    • I’m glad you found this article helpful. The most common culprit is low A/C refrigerant or a leak somewhere. Doing a dye test should help find where that leak is. The next item I’d check is the A/C relay. A/C compressors are known to fail and sometimes they can be rebuilt but if it makes sense just to replace it altogether, I’d go that route. What kind of car does your brother have and what all is he planning to replace in the A/C system?

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      • Replacing my compressor and accumulator blower motor works good bc heat blows good thermostat and ac charge are my only 2 conclusions on why my ac isn’t working I’m getting in vacuumed and charged today but if that doesn’t work idk what else it could be any ideas?

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        • When they re-charge they’ll most likely add dye to it if the shop suspects any leakage in the A/C system. Let us know if you get your A/C working again. It’s getting hot out there especially here in Georgia!

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  2. very good post for readers who are looking for a compressor. I really enjoy it and read it carefully I get some information. I hope you will share some more info about compressors with us I absolutely love this site. Thanks
    peças para compressores

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  3. Thank you for a great write-up! I’ll be bookmarking this site. I was wondering if you know what could be causing my issue. Once the a/c works, it works great. But to get the a/c to start, 90% of the time, I have to press the gas 1-3 times, in neutral. I can do it in gear as well but it’s just quicker to do it while in neutral. Once it engages I do NOT have to keep pressing the gas, it just works. Then I won’t have to do this again unless I turn my engine off and have to turn it on again. Thanks again. Have a great day!

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    • That’s a very unusual issue where you have to put it in neutral to make the A/C system work. What year, make, and model is your vehicle?

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  4. HELLO

    I was driving going to work and my ac is working perfectly fine…very cold… but suddenly it just stopped blowing cold air while driving.

    Upon checking, when I tuned on the the ac button the aux fan is engaging but the compressor is not engaging.

    What is the problem and what need to check? thank you

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    • It depends on what year, make, and model since several specific vehicles can suffer from a similar issue that’s common in the A/C system. Either low refrigerant or relay is typically the most common issue. If both of those check out, it could be the A/C compressor at fault. I recommend troubleshooting the easiest components like the relay, and fuses, and then diagnosing further.

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        • A great feature of the Audi/VW vehicles and many other makes that share this similar feature is that they have a built-in climatronic (climate control) self-test diagnostic mode that will give you a code in reference to where the issue might be. This helps with troubleshooting.

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  5. I have a Mazda 5 which is not blowing cold air. I have checked the fuse and relay by swapping them with other fuse and relay on the fuse panel but no success.
    Another thing that I notice is I think my compressor clutch is always engaged ie I see it rotating even when the heat is on or A/C is off or even the blower. Does mazda 5 compressor clutch is always engaged ??
    I also have a engine light on because of thermostat issue which makes the engine believe its running cold – I suspect that is not the issue if you have other opinion ?

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    • The two most common culprits are a faulty relay or a failing thermostat. The A/C fan is most likely on constantly because it doesn’t know when to turn off. If you’ve already confirmed via diagnostics that you have an issue with your thermostat, I’d start by replacing that first.

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        • For that year, make, and model the A/C relay should be inside the battery junction box. Pull out the relay C1008, inspect the pins for any corrosion, wiring going to and from the junction box where that relay is located, and if you have a multimeter you can test the relay itself.

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  6. Hi I have a Ford F250 I took my truck in because my Ac was running hot they replaced the compressor and the compressor clutch and the condenser and pressure switch then it worked for a day and quit.I never had a problem before this with my ac.Then I took it in again after spending over 2000.00 and the said it was a fuse it blew cold but not ice cold

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    • Sorry to hear about your pickup truck A/C troubles. It depends on what year that Ford F250 is. Certain years share more design flaws when it comes to particular weak points of the A/C system. If the compressor clutch and condenser were already replaced the shop you took it to more than likely installed the new A/C refrigerant. If there is a certain load on the system it’s not uncommon for the fan blower motor relay or fuse to blow. Depending on the climate I also check the cabin air filters to see if they’re clogged up, which can cause the A/C system to become more strained and lead to component failure.

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  7. I have a 2011 yukon xl. I went turn on the A/C today and the light blinked 3 times which the owners manual says happens it doesn’t have access to the air compressor. I changed the fuse for the compressor and it’s still not working. Guessing it not coolant if it doesn’t have “access” and won’t turn on. Next thing to check?

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    • If the A/C light is blinking 3x, this usually means something isn’t properly calibrated for the A/C to function. It’s either the “mode control” that’s in the wrong position which can cause the A/C not to work in defrost mode, or the A/C isn’t kicking on. Try this calibration reset procedure:

      1. First start up your vehicle and turn your climate control completely off.
      2. Perform a hard battery reset procedure by turning the vehicle off. Disconnecting the car’s negative terminal cable and let it sit for 20-30 min.
      3. Now disconnect the positive terminal cable and touch both the positive and negative battery cables together for at least 30 seconds (make sure you don’t let the cables touch the car battery when shorting them out).
      4. Carefully, disconnect the cables from each other and re-install them on the car’s battery.
      5. Let the vehicle sit for at least 15-20 min.
      6. Start up the vehicle then proceed to turn your climate control on. It should be re-calibrated now. This will re-calibrate blend door actuators and sync everything back up.

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  8. Hi
    I have a 2012 Nissan Sentra. The air conditioner was working and it quit working all of a sudden.

    I was checking the wiring to the compressor and did not find power going to compressor with engine running and AC switch on.

    Unfortunately, Nissan has the relays built in to the IPDM not allowing to check for power.

    What do you suggest would cause no power to compress?

    Thanks!

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    • Hi Ray, as far as I’m aware the fuses and relays are not soldered in for that specific year, make, and model. They should be removable. Even if they’re not a good way to troubleshoot and diagnose the issue is by using a positive fused jumper wire to bypass the A/C compressor clutch relay. If the A/C compressor still doesn’t engage, run another fused jumper wire directly to the A/C compressor, this time for the ground.

      If the A/C compressor turns on, use a test light to see where in the wiring harness the signal is dropped. It will also help to have a good OBDII scan tool to scan for any codes and command the A/C system to check if it responds properly. Hopefully, you find the issue and are able to resolve it!

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