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Tuesday, September 02, 2014

Doug's Domain

Doug Vetter, ATP/CFI

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July 28, 2006

More Aux Fan Fun

I took the car in today for its appointment to have the A/C Compressor and Dryer replaced. I told my technician of my recent success in testing the fan and thought the refrigerant pressure switch was the culprit. After all, by sending voltage to the coils of the low and high speed relays I verified the relays themselves as well as the fan were in good shape, but the fan was still not running after several minutes at idle with the compressor running. Something was still wrong with the system.

He suggested that it's very rare to replace a compressor and they usually fail only because they've been run low on oil. That certainly wasn't the case here, but we couldn't ignore the compressor chattering. He reiterated that the compressor can get noisy if its working at higher-than-normal pressures and he'd need to spend some time troubleshooting the problem before he would feel comfortable changing the compressor and dryer outright. I agreed to leave the car with him for the day, and I got to drive an X3 around some sharp corners and scare myself. No, it's not a Coupe by any stretch.

Anyway, later in the day my technician let me know the culprit turned out to be the low speed relay after all. With the fan disabled, refrigerant gauges on the system showed the high pressure side peaking at nearly 350 PSI, while a typical maximum on this 90 degree F day was more like 250 PSI, simply due to a lack of airflow over the condensor. He didn't have the relay in stock so he ordered one and rigged the old relay contacts to remain closed at all times so the fan ran in normal speed mode continuously while the A/C was on -- not a perfect solution, but sufficient to confirm that the compressor itself appeared undamaged. This fix eliminated 90% of the noise as the running pressure dropped dramatically.

The remaining 10% of the noise appeared to come from the belt and idler pulley. He removed the 1-month-old A/C belt to find it in pretty bad shape -- apparently the extra load on the compressor had taken its toll on the belt. Upon closer inspection he then saw grease leaking from the A/C belt idler pulley (the only pulley we didn't replace during the cooling system overhaul). Naturally, he installed a new pulley before installing a new belt and later remarked to me that the compressor is now "quiet as a mouse".

The good news is that these fixes have eliminated the noise from the compressor and repaired some critical components of the A/C and cooling systems. The bad news is I have no idea how much damage I've done to the compressor over the years it's been running like that. For now, it seems, I'll avoid the cost of a compressor, but I'm still somewhat concerned about how long it will last. And I'm also concerned about the dryer, since those are known to fail and clog up the expansion valve with dessicant. I figure I've just put off the inevitable, but that's okay with me. I have several more pressing things to spend money on.

Total Mileage: 130764, Labor $255, Parts $75, Total $352.