About a month ago, Cathy told me her AC was making noises. I checked and sure enough, the noises were coming from the compressor. We still had AC when moving along. The sound just got louder so I knew it wouldn't go away. Last weekend, I changed the compressor, filter/drier and expansion valve. With the system disassembled, I back flushed the entire system. Including the compressor, there was very little oil in the system and no sign of debris. I did notice that the clamp/retainer on the refrigerant behind the expansion device was upside down in relation to the book diagram, so I assumed the problem may have been caused by someone working on the system and never adjusting the oil properly. I added the proper amount of oil according to the manual. I left the vacuum pump on the system for several hours, then added a static charge of refrigerant into the system and let it sit overnight, since it held a vacuum so well, I assumed it would hold pressure, which it did. Sunday afternoon, I reclaimed the refrigerant and drew the system back into a vacuum and let it sit about two hours while I did some cleaning on the car. Vacuum held, so I charged 700 grams (plus about 20 more-the manual specifies 700+50tolerance) using a digital refrigerant scale. System ran very well, very cold, very quiet. Then it started making a very intermittent rumbling noise that lasts about 5 - 10 seconds, maybe about every five miles, especially when idling at a stop. Just a low frequency roar, not very loud and not like a mechanical knock. The compressor clutch stays engaged and the cold air is not interrupted. I have noticed several related threads, but hope we can all get to the cause on these. I am lucky in that I was a marine engineer for most of my professional career and have all the nice goodies to service AC systems. My best guess as of right now is some resonance in the expansion device, but am not sure. I will follow any leads and get back after trying everything this coming weekend. Thanks. Cathy starts school this week and needs her mechanic back.
