Where Is the AC Compressor Relay Located

Where Is the AC Compressor Relay Located

When there is a malfunction in the car AC system, the first thing we should check is the AC compressor relay. Then, where is the AC compressor relay located?

AC compressor relay is located in the fuse box which is in the engine compartment.

Last summer, the AC system in my car suddenly stopped working and started to blow hot air. The problem was with the AC compressor relay. After deep research, I was able to locate the AC compressor relay and diagnose it. In this article, I will explain how to find an AC compressor relay and how I diagnosed it using a paperclip.

What is an AC Compressor Relay?

AC compressor relay place on a table

The AC compressor relay is an electrically operated switch. There are two main circuits in an AC compressor relay. The primary circuit is connected to the 12V DC supply that comes from the battery. The secondary circuit contains the load which needs to switch on and control the AC compressor.

What Are the Types of AC Compressor Relays?

There are two types of car AC compressor relays.

Relay TypeAdvantagesDisadvantages
Electromechanical relayAffordable Widely available Simple operationLimited lifespan Prone to arcing
Solid-state relayNo moving parts Faster switching Longer lifespanHigher cost Heat dissipation High sensitivity to voltage fluctuations

The most common relay type used for car AC compressors is the electromechanical relay. The main reason behind this is its reliability and compatibility.

What Are the Symptoms of A Bad AC Compressor Relay?

The main symptoms of a bad AC compressor relay are inconsistent cooling and the AC compressor not turning on.

Inconsistent Cooling

Problematic AC compressor relay provides weak or intermittent power to the compressor. So, the AC compressor doesn’t function properly and results in inconsistent cooling.

AC Compressor Not Turning On

This is the most common sign of a faulty AC compressor relay. In this case, you will not hear the compressor’s clicking noise when you turn on the AC. It also indicates a lack of power due to a faulty relay. This can also happen for other reasons, but the relay is the main culprit.

Where Is the AC Compressor Relay Located?

So, where is the AC compressor relay located? Here I will mention how I accessed and test the AC compressor relay.

Step 1: Disconnect the Battery

It’s very important to disconnect the battery when working with the electrical system of the car. Therefore, first I turned off the power by disconnecting the negative battery terminal.

Step 2: Locate the Fuse Box

Fuse box of car with relays

Then I located the fuse box. It was on the driver’s side of the engine compartment.

Step 3: Identify the AC Compressor Relay

I used the owner’s manual of my car to identify the relay of the AC compressor.

Step 4: Inspect the Relay

First, I visually inspected the relay for any signs such as burnt marks or melted plastic. There was no such thing.

Warning: If you notice any of those signs, the relay is problematic and you should replace it.

Step 5: Test the Relay Using the Paperclip

Then I tested whether the problem was in the AC compressor relay or any other components by using a paperclip.

I found the open and closed positions of the relay from the diagram on the relay. In my case, it was labelled “30” and “87”. Then I identified the “30” and “87” relay pins.

Next, I took a paperclip, straightened it out, and inserted one end of the paperclip into the “30” pin and the other end into the “87” pin.

Then I started my car and turned on the AC. Done! The AC worked as before. It meant the problem was with the AC compressor relay.

Step 6: Replace the Relay

I went to a local spare part shop and bought a new AC compressor relay and replaced it.

Note: Please remember to take the old relay with you when you go to a shop. It will help the merchant decide on the correct relay that your car needs.

How To Test the AC Compressor Relay Using a Multimeter

You can test the AC compressor relay using a multimeter.

Set the multimeter to resistance mode.

Place the probes on the open and closed terminals of the relay. (Refer to the diagram on the relay to identify the terminals) If the relay coil is in good condition, the multimeter should display a resistance reading between 2.0 and 5.0 ohms.

If you get a value outside this range, it indicates that the relay is malfunctioning.


How long do AC compressor relays last?

The compressor relay’s lifespan is expressed in cycles rather than miles, or the number of times it is switched on and off. The majority have a 50,000-cycle rating. This often equates to ten years of driving for the average user.

Why would an AC relay fail?

After years of consistent use, the electrical connections may deteriorate. Relays may also overheat, particularly if an issue with another AC component causes excessive power to flow through the relay. It’s fairly uncommon for a relay’s plastic enclosure to burn out or even melt due to a defective component.

Can a AC compressor stop a car from starting?

Yes, if the AC compressor is locked up, the starter motor’s power will not be enough to turn the engine to the proper speed. In large trucks, the AC compressor can take 12HP from the motor while in small cars it can take up to 8 HP. If the engine turns but the car won’t start, there may be a spark or fuel issue.

Why is my AC compressor smoking?

That smoke comes from the AC compressor clutch. Overcharging the system leads to a defective compressor clutch. In this case, you need a new compressor. At least bypass the AC compressor because a malfunctioning one affects other important components such as the alternator.


Again, where is the AC compressor relay located? It is in the engine compartment and you can easily find it in the step-by-step guide that I provided here. Thanks for reading and have a nice day!

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