How to Test Car Ac Compressor with Multimeter

Test Car Ac Compressor with Multimeter

A car compressor is an essential component of the HVAC system. An AC compressor compresses the refrigerants and provides cooling or hot air. A faulty AC compressor is your car effect’s the air conditioner’s performance, making your experience poor and worsening your vehicle’s performance. In this post, we’ll learn how to test a car AC compressor with a multimeter. But first, understand how an AC compressor works.

The compressor is basically the heart of the HVAC system that pumps refrigerants to the whole system. The compressor applies pressure on the refrigerant to compress and use them to change the temperature.

A compressor clutch is an electromagnetic unit that activates the compressor pump when a signal is sent through the power control module (PCM). The AC compressor clutch is responsible for converting the power supply from the engine and supplying it to the compressor.

A refrigerant is a gaseous or liquid compound used in HVAC systems. It rotates in the HVAC system, absorbs heat from the air, and gives a cooling effect.

Refrigerants and compressor play a vital role in compressing the refrigerants, which absorbs temperature in your vehicle’s cabin.

What is AC Compressor?

The ac stands for air conditioning. When you notice that your ac is giving the hot air on the more hot day, it probably has a bad compressor or faulty component. In the case of a defective ac compressor, it will lead to engine failure.

It causes the car to stop moving when you are driving, and It leads to injury. The bad compressor also affects the steering and the brake because the power line is limited. So, the AC compressor is vital in producing fresher air and ensuring circulation in the entire AC unit.

You can quickly fix the faulty compressor. For this, you have to perform the test with the help of a multimeter to determine where the problem is occurring in the AC unit.

Car ac compressor failure symptomsCar ac compressor

The most common symbol of compressor failure is:

  • Poor air conditioning performance.
  • Dropped and irregular performance of the Air conditioning system
  • Refrigerants (moisture) leaks.
  • The HVAC system may overheat or doesn’t cool the air,
  • Loud noise from the AC compressor or engine compartment.
  • Compressor clutch stocks and don’t engage.
  • The electrical failure leads to the AC clattering or rattling sound in the AC compressor.
  • You may have to face a hard time while starting the AC compressor.
  • The AC may start blowing the cold air.
  • Many problems can occur with the circuit breaker.

You can also Troubleshoot the AC Compressor in the following ways:

  • Calculate the discharge pressures
  • Observe the pressure of the discharge line
  • It would help if you recorded the temperature of the refrigerator space
  • You should test the compressor valve
  • You should also check for faults, so you should monitor the electric motor

How to test car ac compressor with a multimeter?

To test a car AC compressor:

  • Locate it and disconnect it from the power supply.
  • Set your multimeter to DC voltage and check the voltage in the compressor clutch and another pressure switch.
  • Ideally, the voltage should be around 12V.
  • Also, measure resistance in the pressure switch terminals and compare the multimeter reading with the ideal ranges.

Follow the guide to test your car’s AC compressor.

  • Visually inspect the AC compressor

Before examining your car’s AC compressor, make sure to power off the circuit, as accidental contact with live wire can result in electric shocks.

After that, visually inspect for any physical damage to the AC compressor. Unscrew the compressor from the engine and check for any broken wires, terminals in connectors and plugs, and damage to the compressor’s body.

  • Test voltage in the compressor clutch

We’ll test the voltage supplied to the compressor with a multimeter.

First, we’ll locate the compressor in the car’s engine. The car AC compressor is located in the front of the engine bay with other components in the accessory belt configuration.

To test the voltage supply of your car’s AC compressor, disconnect the power connector from the compressor clutch.

Set your multimeter to DC voltage. Insert the red multimeter probe into one terminal in the compressor clutch terminal. Connect the second probe to the battery’s negative terminal.

Most of ac compressor clutch in cars works on 12 V (battery’s voltage). That’s why if your car’s ac compressor is fine, the multimeter should read 12V in the compressor clutch.

If the voltage reading is relatively low, the compressor wiring is damaged, or the compressor is faulty, leaking the current.

  • Measure resistance in the pressure switch

The pressure switch in a car’s AC monitors the refrigerant’s pressure. The pressure switch is located on the high-pressure side of the loop.

Set your multimeter to ohms at a high range to test resistance in the pressure switch. Connect one multimeter probe to terminal 5 and the other probe to the 7 terminal on the low-pressure switch.

Resistance is not directional, so you can touch multimeter probes in any direction.

If your multimeter reads 0 or quite low resistance, then it means that the pressure switch has excellent continuity. However, the pressure switch circuit is broken if your multimeter reads OL.

In the same way, test continuity in the 6 and 8 terminals on the high-pressure side.

Read the multimeter and evaluate if the high-pressure switch is fine or not.

Test AC Compressor with the Help of a Multimeter:

Here are the 5 steps to test an ac compressor with a multimeter in more detail in a step-by-step guide.

Step 1

Before monitoring your AC compressor, you must ensure that the AC compressor switch is switched off completely. Doing this would help because it helps you avoid getting electrocuted. After this, remove the AC unit’s face plate by unscrewing them. Because it will enable you to come in touch with the elements on the inner side of the unit.

After this, remove the power access panel to check how the wires are attached to the AC compressor unit. So you can check the burnt or terminals.

Step 2

You should ensure no connection between your power connector and the clutch compressor. You should set the multimeter to the direct current. Connect the one positive probe with the terminal. This positive probe leads to the port of the clutch energy. And then makes the connection with the negative probe.

After testing the AC, .you should start the engine. It would help if you observed the voltage displayed on the multimeter. You should move the probe to the next connector if it says zero.

You should move the negative probe to a different terminal when it still shows zero. At the time when you have placed both of the probes on the power connector, it means that both the ground and clutches are receiving the adequate power supply.

Step 3

Connect the battery’s negative terminal with the negative probe to determine the power flow between terminals 2 and 3. Connect the positive probe with terminal 4 and the negative probe with terminal 3.

Step 4

Then start your car engine. Turn your AC to its maximum for the monitoring of the voltage that is shown on your multimeter. in the case when you have the power on all of the switches. Then you need to perform the continuity test across all of the switches.

Step 5

Set the multimeter on the ohm, then attach the one-meter lead to the particular terminal placed on the low-pressure switch and link the other with terminal 7. When the switch is closed, the pressure of the refrigerator is perfect.

Frequently Asked Questions

  • How to check if the car AC compressor is working?

To check if the car AC compressor is working, turn on the engine by rotating the ignition key.

Turn on the AC by pressing the AC button. Also, press the recirculation button. Now head toward the engine and check if the compressor clutch is spinning.

If the compressor clutch is usually spinning and stops, eventually, the compressor works fine. If the clutch doesn’t spin even after minutes, then the compressor is facing an issue, which could be due to a low refrigerant level.

  • How to know if a car AC compressor is bad?

Poor air conditioning performance, sound from the compressor, compressor clutch not spinning, low refrigerant level, low cooling, and high temperature.

  • How to test the AC compressor clutch coil?

The black wire in the compressor clutch is ground, and the yellow is positive (live). Check the voltage in the compressor clutch with your multimeter. If the clutch is working properly, it should have above 11V.

A car AC compressor clutch can also be visually checked. Run the engine and turn the AC and recirculation on. Check if the compressor clutch is spinning or not.


So how to test a car AC compressor with a multimeter? Testing a car compressor is essential for your HVAC system to work constantly.

Use a multimeter and check the voltage and resistance in the compressor clutch and other switches.

Make sure to compare the multimeter readings with the ideal range of your specific compressor model to check if the compressor is working with enough voltage and if there is continuity in the components.

If you still have any queries, let’s ask us in the comments.

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