Is high engine temp really all about AC? - PeachParts Mercedes-Benz Forum

ksing44 · #1 07-11-2007, 05:48 AM

Well, it was in the mid 90s for a couple of days here in PA. Sure enough the Cool Harness V2 has the aux fans come on high speed at about 95 degrees and then they don’t turn off until you turn off the car. Too bad. In more normal temperatures, the aux fans never even come on at high speed, but in the very high heat it is on and never off.

The good news is that before the V2 install my car was doing pretty good with the heat. It seems that my fans running at low speed, from the AC pressure, keeps my car under 100 degrees with no problem. My aux fans were not responding to AC system pressure before, since my system was a bit low on charge. It still got cool in the car, but the charge was low. Now with a new full charge, the aux fans do come on low speed quite frequently and that seems to keep the car running cooler without going to the higher temperature that kicks in the high speed.

Now I am thinking that maybe the W124 would not run so hot if everyone had good AC systems with a full charge. The real weak link might be keeping a full charge in the AC system, since it seems everyone has issues with them. The AC system just leaks. Sooner or later it just happens. If you are lucky, it isn’t the evaporator. I am on my second leak in 10 years. The first was the expansion valve to receiver drier. This time it is the compressor.

Is it possible the Mercedes actually designed the car to stay cool in most normal situations by responding to AC pressure and that the high speed fan is really just a kind of emergency fail-safe kind of thing? It makes sense that you would have the AC on if it is hot, so why not depend on the AC? They also seem to have designed the car to use AC even in winter driving to control humidity. Maybe they just figured AC would always be on.