My AC Cooling Stops After 30 Minutes or so in Skoda Fabia 2008: Compressor or Electrical Problem?

Question

I own a 2008 Skoda Fabia, and recently I've been experiencing an issue with the AC. It cools fine for about 30 minutes, but then the cooling stops, although the fan keeps blowing air. To get it working again, I have to turn the car off and on.

I visited a local AC technician who thought the issue was with the compressor wall, the high-pressure switch, and the water pump (since he noticed the engine was running hot). I replaced all of these parts, but the problem persisted. While replacing the compressor wall, I noticed a black oil-like substance leaking from the compressor. However, the technician assured me that if the compressor or condenser were the problem, the cooling wouldn't work at all, not even for the first 30 minutes. We also tried removing and reinserting the same evap sensor below the steering wheel and noticed that the pipes were getting frozen when removed and the ice melted when inserted.

I then took the car to a different technician, who tested the power supply to the compressor by attaching a light bulb to the compressor wire. After about 30 minutes, the light went out, indicating the power was being cut off. When the car was restarted, the light and the AC came back on. He was certain that the issue was electrical, not with the compressor or the AC system itself, since the cooling would restart once the power was restored.

We scanned the car, and the only error that came up was related to the drive battery voltage ("implausible signal"), which the technician said wasn’t related to the AC issue. He ran tests on various car modules, and while checking, the wipers activated randomly, and the AC started cooling again, only to stop after 30 minutes as usual. Despite the tests, no significant errors appeared, except for the battery voltage issue.

The technician now believes the problem lies with the Body Control Module (BCM) and suggests it needs replacing. I'm unsure if this is the real issue, especially since I initially thought the black oil in the compressor indicated a fault with the compressor or condenser. Could it be the BCM, or is there another potential cause? I’d appreciate any advice. Please help. Thanks

Answer 1

Are these techs trained on vehicle ac systems? What do you mean by "compressor wall"? A 2008 is now 16yrs old, old enough for normal wear and tear with one fact universal to vehicle ac systems; the leak no one wants to address. Virtually all ac systems have protection sensors to disable compressor operation when refrigerant leaks out. Your system may be low on refrigerant. Refrigeration gauges and a person familiar with operating pressures can determine if your system leaked and lost refrigerant that may be contributing to intermittent operation. In addition, the cooling fan must run when ac runs; it forces airflow thru the hot ac condenser coil in front of a hot radiator. A dead or failing cooling fan(s) can diminish ac operation from higher operating pressures by sensors automatically disabling compressor operation.

Answer 2

30+psi/low side seems a little lower than ideal, 200+psi/hi side appears higher than normal. Does the cooling fan run or not? The cooling fan always runs when ac is running. A dead or slow running (worn out) cooling fan will allow discharge/high side pressures to increase to dangerous levels when the combination low/high pressure sensor detects out of range values and sends a disable signal to the ecm. The ecm disables compressor power until pressures subside; system pressures equalize - high pressures lower, low pressures rise until the high side pressures drop to safe operating pressure when the pressure sensor detects it and sends a signal to the ecm to enable power to the compressor.

Open the engine hood with engine idling, ac off. On a warm day, the cooling fan may run or not, depending on engine coolant temperatures. Pressurized cooling systems run as hot as 220F/104C when the cooling fan turns on and turns off when coolant temps drop below approximately 210F/99C.When ac is turned on, the cooling fan turns on immediately to force airflow thru ac condenser coil and hot radiator to prevent ac pressures from rising above a certain pressure, and coolant from overheating. If the cooling fan runs at low speed when ac is turned on, it may be worn out. On very hot days, the two speed cooling fan should alternate between low and high speed with ac running. On hot days with ac on, in stop and go traffic, the fan should be running at high speed.