Compressor Not Engaging
The clutch oil starts to energize when it is being powered. A magnetic field is created and it draws the clutch in so that it engages the shaft of the compressor. If the clutch fails to engage, the A/C compressor of your car will not be able to pump refrigerant in the way it is designed to. In this case, it is recommended that you kickstart your diagnosis by determining if there is a working compressor clutch.
How Does a Car A/C Compressor Engage?
A majority of car manufacturers utilize an electro-magnetic clutch to disengage and engage the air conditioning compressor. As mentioned, the clutch is pulled in towards the pulley via a magnetic field. The clutch disc will then be splined to the compressor shaft. When this happens, the pulley also provides the rotating power needed to operate the compressor. If the clutch successfully engages, the air conditioning compressor will proceed to pump refrigerant.
So, what should you do if the compressor does not engage? Try turning on the A/C controls to MAX A/C and start the engine. Next, look at the front of the compressor clutch. You should be able to see both the clutch and pulley spinning. If this is happening, this means that the clutch is properly engaged with the pulley. If you see only the pulley turning, this indicates that there is a problem somewhere in the system.
What’s Preventing the A/C Compressor from Engaging?
One of the reasons why compressors do not engage is because of a low pressure lockout, a poor ground, a bad clutch coil, an opening in the wire to the clutch coil, or simply a blown fuse. There are several ways A/C compressor clutches receive power. One, the relay can be operated by the PCM (the PCM interprets the condition of the low and high pressure sensors). Two, the clutches activate through a relay that’s energized directly by a certain condition of the low/high pressure switches. That’s why it is good to start the diagnosis by checking the compressor clutch fuse.
Let’s say that the fuse is good. You can disconnect the compressor clutch coil from the electrical connector. Make sure it is moved away from any moving parts before checking the power and ground. With engine running, you will want to set the A/C to MAX. If you have a digital voltmeter, you can check for battery voltage.
Do keep in mind that wiring varies by year, model, and make. Some car manufacturers trigger the relay control coil ground via the ECM or PCM. There must be a good signal from the evaporator temperature sensor, high pressure switch, and low pressure switch for the computer to provide ground.
Can You Charge a ‘Dead’ Compressor?
Yes, you can. You need to start by connecting the recharging kit to the suction. Note that the low pressure tubing always has a larger diameter than the high pressure line. In addition, the kit fitting only attaches to the low pressure port. Next, turn the key to RUN and the blower fan to HI. Start the radiator fans by turning the A/C to MAX. Now is the time to start adding refrigerant.
Does your car use an orifice tube system? In most cases, the refrigerant gas will enter the condenser coil via one of the open compressor reed valves. Let the blower fan run for a few minutes. After that, you should have enough pressure to close the low pressure switch. If nothing works, do not hot wire the low pressure switch, it is recommended that you visit a mechanic to check the issue.