A worn-out pressure-cycling switch can cause air *conditioning compressor clutch failure, service experts warned. Also, ignoring a simple voltage check on the pressure switch can lead to repeated compressor clutch failure. Many technicians are aware that the pressure-cycling switch opens every time low-side refrigerant pressure drops too low, thereby breaking the power supply circuit to the compressor clutch. Then when low-side pressure rises again, the pressure switch closes, turning on the compressor clutch.
But many people forget the switch is a high-wear component because it operates every time the compressor cycles on and off. Worn or burnt contacts inside the switch reduce voltage and current to the electromagnet inside the clutch.
Reducing electrical energy to the clutch lowers its holding power, allowing it to slip. Eventually, this slippage causes total clutch failure.
As explained elsewhere in this service section, compressor clutch failure has become costly today.
Usually, it's no longer cost-effective to change just the clutch. Instead, the entire compressor/clutch assembly is replaced.
Because the pressure-cycling switch is such an active component, many service technicians routinely replace the switch whenever they replace a clutch or complete compressor/clutch assembly. They explain to the customer that the relatively low cost of a new switch is cheap insurance against repeated clutch failure and an expensive comeback.
Others replace the switch only if it fails a voltage drop test. To do this test, connect a digital voltmeter between the positive battery terminal and the positive or power feed terminal of the compressor clutch. With this hookup, the voltmeter displays the voltage loss between the battery and the compressor clutch when the clutch is engaged. Engage the clutch by turning on the air conditioner.
If the voltmeter reading exceeds about 0.20-0.30 volt with the compressor running, trace the power feed wire up to the pressure-cycling switch and carefully back probe the wire's terminal at the switch. If the voltage loss is still excessive, move the test lead to the other pressure switch terminal and back probe this terminal. If the voltmeter reading now drops near zero with the compressor running, you have pinpointed the voltage loss to the pressure-cycling switch. Replace the switch.