The heater control or PCM isn’t providing ground to the control coil on the AC compressor clutch relay. Remove the electrical connector from the clutch coil and check for good ground using a multimeter. A corroded ground connection will prevent the clutch coil from generating a magnetic field, resulting in a compressor clutch won’t engage situation. The high pressure switch is located on a high pressure line or right on the receiver/dryer. Starting the AC compressor against high pressure, whether due to an overcharge condition or a restricted component can damage the clutch and compressor. The low pressure switch is installed on the low pressure line or right on the accumulator. That’s why you should NEVER jump across a low pressure switch to force the AC compressor to engage. If the compressor operates with a low refrigerant charge, the system won’t carry enough oil to the compressor, causing it to fail. Low pressure indicates a low refrigerant charge. To test, unplug the electrical connector at the clutch coil and test for battery voltage with the AC turned on. The electrical contacts in the AC clutch relay can develop pitting that prevent full current flow to the clutch coil, resulting in no clutch engagement. That would result in a weak magnetic field that prevents full clutch plate to pulley engagement. If the reading is too low, that’s an indication of a short between coil windings. Finally, attach both leads to the two clutch coil terminals and compare the resistance reading to factory specifications. Then switch to the other clutch coil terminal and check for short to ground. To test for a short to ground, set a multimeter to the ohms scale and touch one lead to a clutch coil terminal and the other to a ground point on the compressor. The most common cause of a blown clutch fuse is a short to ground in the compressor clutch coil. In newer vehicles where the AC is controlled by the heater control head or the PCM, the wiring is quite different. When turned on, power flows through the switch and then to a low and high pressure switch before flowing to the compressor clutch coil. In older non-computerized vehicles power flows from a fuse to the AC switch. How does an AC compressor clutch engage?Ĭarmakers use several different wiring methods to provide power to the clutch coil. When the clutch coil receives power and generates a magnetic field, it pulls a portion of the clutch plate against the clutch body/pulley, causing it to rotate the compressor shaft. The clutch plate connects to the AC compressor shaft and drives the compressor when it mates against the clutch body.When the driver requests AC, the system provides power to the clutch coil, thereby generating a magnetic field. The compressor clutch coil is simply a large coil of copper wire.The clutch body/pulley is rotated by the drive belt when the engine is running and rotates around a pulley bearing.How does an AC compressor clutch work?Ĭompressor clutches are sometimes referred to as a magnetic clutch because they operate like an electro-magnet. But the pulley will not rotate the AC compressor shaft unless the compressor clutch has engaged. The AC compressor drive belt rotates the compressor pulley at all times when the engine is running. Some engines use a dedicated drive belt to drive the AC compressor, while others use a drive belt that drives multiple components. A slipping AC compressor clutch is a sign of severe wear, shorted clutch coil or an incorrect air gap (explained later). Unlike a car’s transmission clutch, an AC compressor clutch is either transmitting full drive power to the AC compressor or not-it’s not supposed to provide partial power. Repair Topics > Air Conditioning Symptoms and Repair > Car AC compressor clutch Car AC compressor clutch What is an AC compressor clutch?Ī car AC compressor clutch is used to connect and disconnect drive power to the car’s AC compressor shaft.
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