Another car with an air conditioning problem came in. This time, the air conditioning would work fine for a little while, but then would completely stop working. I hooked up the A/C machine to see what the pressures were doing, and found that as I held the engine at 3,000 RPM, the high side pressure would just climb until it hit around 500 psi and the pressure switch would shut off the compressor.

Our first instinct was that there must be some sort of obstruction in the A/C lines. I checked the expansion valve and evaporator, because they’re relatively easily accessible on this car, and they seemed fine. After looking over the whole system, I noticed that the radiator was clogged with dirt. The condenser is in front of the radiator, and it didn’t look dirty at all, somehow there was dirt caked on the radiator. How it got there I don’t know.

The dirt in the radiator meant that air couldn’t flow through the radiator or condenser. When there isn’t airflow through the condenser, the hot refrigerant doesn’t get cooled down. As temperature increases, so does pressure. Eventually the pressure was reaching when the car’s pressure switch shuts off the compressor so the system doesn’t blow out a hose or fitting. I removed the condenser and fans and sprayed water through the back of the radiator to wash out the dirt, and once everything was back together, the A/C pressures were normal and everything worked fine.

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-Dan