Air Conditioning System - troubleshooting

[bearusmc11]

Here goes my first post on here. 1991 318i 4D.

While driving with the AC on and fan speed at 1, there will be an audible click twice (sounds like a relay) approx every 30 seconds. Click....1 sec....click........30 secs......click......1 sec.....click. With the 2 click of each cycle there is a jolt in power like when you first turn you AC on and it is sapping a few hp. This is leading to assume that the clicking is the AC compressor relay clicking off then right back on in this cyclical motion.

This only happens while on fan speed 1. 2-5 it doesn't happen.

Anyone have an idea why this would be happening?

[tomstin]

Is your AC real cold? On my 85 there is a evaporator temp sensor that prevents the evaporator from freezing and that will shut down the AC compressor. Could it be that the sensor is sensing too cold while little air is moving over the evaporator? Check your wiring diagram, mine on on the driver side of the evaporator.

[bearusmc11]

It is really cold. I wonder if that sensor is malfunctioning because of how often it does it (every 30 seconds) seems excessive. I will look tonight.

[treff-7]

You might be low on refrigerant. There is a pressure sensor that won't let the A/C turn on if the pressure is under or over a certain level.

EDIT: I just saw your comment on the previous post. Does it do this from the point where you first turn the A/C on or only after a while?