Rick's Free Auto Repair Advice

Auto AC Compressor turns on and off quickly

Auto AC Compressor turns on and off

When you run into a situation where your auto AC Compressor turns on and off, that’s often a symptom of low refrigerant charge.

What causes an Auto AC compressor to turn on and off

In some vehicles, the AC system regulates how long to run the compressor by sensing the refrigerant pressure in the AC accumulator located near the evaporator in the dash. In a fully charged system, when the pressure falls below a set-point, the low-pressure switch cuts power to the AC compressor clutch. Then, as pressure rises, it re-powers the compressor clutch.

Low refrigerant charge causes AC compressor to turn on and off

When an auto AC system is low on charge, the compressor actually pulls in refrigerant vapor faster than the evaporator and the accumulator can provide it. That causes pressure to drop, which causes the low-pressure switch to cut off power to the compressor clutch. As soon as the compressor stops sucking vapor, pressure builds and the low-pressure switch turns on the power again. This causes rapid compressor clutch cycling.

Fix a low charge

You may be tempted to just add refrigerant to solve the problem. But this is a sealed system. If you’re low on refrigerant, you’ve got a leak. Worse than that, you have air in the system. You can add refrigerant, but with air in the system, it’ll never cool well. The proper fix is to locate and fix the leak, evacuate the system and then refill.

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Posted on by Rick Muscoplat

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