Wednesday, April 02, 2008
Question: My 1999 Jeep Grand Cherokee had the Air Conditioning compressor replaced in July '07. It worked OK for around 5 months. It Stopped engaging. I had the system recharged and had dye added at the same time. Drove it home about ten miles and it seemed OK. Did not run Jeep for two days. A couple days later I noticed the compressor wasn't engaging. Took it back for the UV light check for the dye. No leaks were found. They tell me that my evaporator core (under dash)is leaking. They can replace it for $750. The compressor doesn't engage but the system seems to have a charge (determined by pushing down the fill stem.) Does this sound right and could it be something else? Answer: Absolutely possible. The A/C system can still have pressure in it, and yet be too low to engage the compressor. The low-pressure cut-off switch will prevent compressor clutch engagement to protect the compressor in the event of a low refrigerant charge, and this condition is normal. The system can still contain some refrigerant (noticeable at the service ports), and will even seem to have a charge with only residual refrigerant (essentially, empty) when pushing down on the schrader valve at the service port. When checking the system with dye, it's often easy to verify the leak by shining the UV light on the HVAC case drain tube. Often times, though, nothing is evident at the drain, and you only notice the leak when the HVAC case is removed and the evaporator inspected (the evaporator is not visible without pulling the dash and HVAC case). I've pulled plenty of these apart, after the UV showed nothing visible *anywhere*, only to find out that the evaporator is green (with fluorescent dye).The cost seems a bit high, but in HVAC system repair, you often get what you pay for. $750, while expensive, is about normal for the dealer, and it's the hardest component to replace in the A/C system.