How to test car AC compressor with multimeter.

How to test car AC compressor with multimeter

As you know, the air-conditioning compressor is a key component in any vehicle with an AC controlled climate system. Its duty is to compress the refrigerant in the system so it can be cooled and distributed into the evaporator. Sometimes air passes over the evaporator before going through the vehicle’s air ducts and into the passenger’s area. So whenever you suspect the air-conditioning system in your vehicle malfunctioning, there are several things you can test to determine if the compressor is faulty.

How to test car AC compressor with multimeter

 

  1. Just turn off your vehicle. You need to turn off the engine so that the moving parts under your hood are stationary. Once your engine or internal parts are hot, just wait for them to cool down before inspecting your compressor.
  1. Now open the hood and find your AC compressor clutch. The compressor clutch will usually be located under your hood on the left side near the front of your car. It will look like a cylindrical metal piece with tubes and wires running from it.

 

  1. Inspect the compressor for damage. The compressors are prone to rust on older vehicles. Inspect the compressor itself for holes or rust damage. Also try to inspect the tubing and wires to ensure that they aren’t disconnected, frayed, or damaged. In case they are, you can replace them more cheaply than it would cost to get an entirely new compressor

 

  1. Try disconnecting the wires running from your battery to the AC compressor. Note that there should be wires running from the top or side of the compressor. Also note that the white wire is your live wire that carries electric current, and while the black wire is your ground wire. Just press on the sides of the plastic fittings and pull on the wires to get them off. Once done, it should reveal the contacts that you’ll use to test the compressor.

 

  1. Now insert the multimeter pins into the plastic fittings to get the reading. Then set your multimeter to continuity and place the pins on the contacts. By setting the dial on your multimeter to continuity, you will test if the current is properly running via the compressor clutch

 

  1. Now replace the coil if the reading is below 3 ohms or above 5 ohms. However, if reading is 0 ohms, it means that your wires are bad and you’ll have to get them replaced. But if your reading is over 5 ohms, it simply means that you have a bad coil, and your diodes should be examined by a mechanic

 

  1. Try to connect your AC compressor clutch to a 12-volt battery and see if it engages. Now connect your negative, or black battery cable with the grounded contact in your compressor. After that, attach the black wire to the negative side of the battery. Then connect the positive, or red wire, to the positive side of the battery.

Now touch the metal end of the wire to the live compressor clutch wire. Once done, this should engage the clutch back and forth. But if the clutch does not move or make any noise, it means there is an issue with the contacts or the clutch itself.

What causes car AC compressor failure?
What causes car AC compressor failure?https://kctimoauto.com/what-causes-car-ac-compressor-failure/

How To Test The Compressor’s Clutches

Step 1

Just open the hood of your vehicle, and find the air compressor. This is located on the upper left-hand side of the engine compartment.

Step 2

Now turn the air conditioner selector knob in your vehicle to an off position, and then start your engine.

Step 3

Now connect the voltage tester to the negative connection on your vehicle’s battery.

Step 4

Find the wires coming off of the ac compressor, and unplug them. Then you can place the voltage tester on each of the three connections individually.

Now turn the air-conditioner selector knob to the on position. Then place the voltage tester on each of the three connections. Right now the middle connection should produce activity on the voltage tester, indicating the connection is hot. But if no activity is noted, then your air compressor clutch and wire should be replaced.

 

How to Troubleshoot Air Conditioning Compressor Motor

The air conditioning compressor motors are very simple to troubleshoot but can be confusing. So if you find that an AC compressor is getting the proper voltages, has a good capacitor, and will not run well, etc. it could be that the motor windings have a problem.

Note that there are only 3 motor winding failures, they include:

  • The Open Winding 

Here is when one of the wires that makes up the motor windings is broken or separated.

  • The Shorted Winding 

Once the insulation on the windings fails, it could be that one part of the winding is making electrical contact with another part of the winding.

  • The Grounded Winding 

Here’s another one similar to the shorted winding. Instead, the wire with the broken insulation is making electrical contact with the compressor casing or ground.

Note that any measurement that doesn’t read infinite indicates a grounded winding.

Sometimes these measurements are very difficult to make because there is usually a shroud around the compressor terminals. Meaning you have to stand on your head to get to them. But if you can, find a scrap AC unit at your environment and grab a compressor plug, then strip the 3 wire ends.

Whenever you take off the compressor plug, you can plug-in your plug with the bare wires and easily make your resistance measurements.

 

Conclusion on how to test car AC compressor with multimeter

As we said before, an air conditioning compressor creates cool air by circulating refrigerant through your AC unit. So if your AC isn’t working, there’s a good chance that a faulty compressor could be the problem.

So you can diagnose the problems with your compressor by using a multimeter. You can also use a device that can measure volts, amps, and ohms.