E21 BMW ac problem
 

PPOT braintrust I present my problem.

1981 BMW 320i. The AC compressor cycles on then shuts off if you try to turn on the interior fan blower, then both do not work.

If I turn off the interior fan blower the compressor cycles back on, if I turn off the AC the fan will turn back on, both will not run together.

I suspect there is a relay issue, cannot find which relay.

Thanks in advance if anyone has personal knowledge and experience with this issue.

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From your description it sounds like the relay / circuit is not holding a load. I have seen time and time again the relay(s) 'work' but when 'X' load is placed the contact points will not flow enough amps to sustain current because they are pitted / corroded.

You should find which relay it is, replace it with correct amp rating ( it's printed on the side) they are inexpensive. If no success you'll need a schematic for that to start performing voltage drop tests to find the issue

I think you are on the right track, I had a e21 for a while years ago, can't help you with the relay position but you should check the contact surface of the fuse also. Could be wired direct through the switch?

http://bmwtech.info/BMW%203%20(E21)/Wiring%20Diagram/ETM_1981-1983.pdf

Page 9

Thanks for all the replies.

Actually 4-6 contains the answer I was looking for the AC Relay is on a dash brace under the right side of the dash, I was going crazy trying to locate it in the fuse box.

I know where to look now. I figured the perfect 1st step was to replace the relay, I now know where to find it.