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Yes, no pressure switches (archive)
[ Follow Ups ] [ 5-series (E12) Message Board ] [ Msg. Board FAQ ]
Posted by Mike W. on March 26, 2002 at 01:14:41:

In Reply to: E12 AC clutch? posted by Chadtoolio on March 25, 2002 at 18:30:51:

I could probably find it but it would take a couple of days to get a schematic off to you, but there are no pressure switches, either high or low. Basicly though, they do the switching thru a microswitch (and relay) and a mechanical thermostat off the temp switch. The relay switches voltage from the heater blower to the A/C blower and feeds the thermostat which in turn goes to the compressor clutch and the aux fan. Those old Bosch compressors do run a long time, the one on my old (ex) 79 528i is still working at 357k. No experience with the R134a changeover but be advised the most likely source for leakage is the hoses, especially on the high side. I replaced a couple when I got mine at 197k and it has had one minor top off since then, about 10 years and 160k miles.
Mike

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