Author Topic: A/C compressor wont engage (Read 6551 times)

Bimmer805 · « **on:** August 19, 2012, 09:37:30 PM »

so about a year ago i cut my a/c belt becuase it wasnt blowing cold and i didnt need it well recently i installed a new belt because i want to recharge my system and i want my a/c back. well turns out when i press the a/c button the aux comes on but the a/c compressor wont engage at all. how do i fix this problem please help:(

DesktopDave · « **Reply #1 on:** August 20, 2012, 06:53:59 AM »

Might be that the clutch is shot, or that the pressure switch isn't working. I've never done any A/C work on the e30 so I'm not sure which one to short, but the pressure switch is up near the passenger headlight on the receiver/dryer.

Bimmer805 · « **Reply #2 on:** August 20, 2012, 10:31:59 AM »

Oh ok I check for power there and I didn't get anything

Bimmer805 · « **Reply #3 on:** August 20, 2012, 04:39:03 PM »

i have check for power on the pressure switch and im getting no readings

DesktopDave · « **Reply #4 on:** August 20, 2012, 07:41:44 PM »

Did you download the e30 electrical troubleshooting guide yet? Definitely get that - it explains all this stuff. I grabbed the '92 318ic version as the '91 318 has some missing pages:

http://wedophones.com/BMWManualsLead.htm

Lemme see if I can post it somewhere, it's only about 10MB zipped. Or PM me an email address and we'll see if it'll go.

DesktopDave · « **Reply #5 on:** August 20, 2012, 07:55:46 PM »

Looks like fuse 20 feeds the A/C switch with a white wire, which powers up the 'evaporator temp regulator' unit, runs the aux fan on low, and lets Motronic know that it should bump up the idle with a black/violet wire.

You might be able to test this by seeing if the A/C switch turns on the aux fan in front of the radiator. Should happen with the ignition switch in position I or II.

Once the HVAC unit is running, looks like it uses two controls. There's that pressure switch (may be two switches on earlier models) and a evaporator temp regulator (not sure what that is though). Those send a signal to the 'compressor control unit' over a black/red wire. That control unit then finally switches power from a green/black wire to a black wire that powers the compressor clutch.

Bimmer805 · « **Reply #6 on:** August 20, 2012, 10:27:48 PM »

I push the snowflake button and the aux fan does come on

DanOKC · « **Reply #7 on:** August 20, 2012, 10:56:40 PM »

If the system has lost most of the freon, the pressure switch will keep the compressor from coming on. Try to jump across the pressure switch terminals with a short jumper wire to see if the compressor clutch engages. The pressure switch will cut off for too low pressure or too high.

I had to jumper mine to start charging it last year. Once you have a minimal charge, you can remove the jumper, & reconnect the terminals to the pressure switch.

Best bet would be to evacuate the system with a vacuum pump, make sure it holds, then recharge.

Bimmer805 · « **Reply #8 on:** August 21, 2012, 01:43:24 AM »

how do i go about jumping the terminals?

DesktopDave · « **Reply #9 on:** August 21, 2012, 05:59:48 PM »

Pull the connector off the switch & put a short bit of wire into the wiring harness connector. I don't think that carries much current, so a paperclip bent into a u shape might work well too...but be sure you don't test any ignition components that way...

DanOKC · « **Reply #10 on:** August 21, 2012, 06:43:14 PM »

Follow the wires off the switch about 10 inches away from the switch, there is a connector there that you unplug, squeeze the tabs & pull the connectors apart. Put the paper clip or wire in there. Do this for just a few secs to see if compressor kicks in.

Bimmer805 · « **Reply #11 on:** August 22, 2012, 04:58:50 PM »

theres one like a three prong and theres one with a two prong which is it?

DanOKC · « **Reply #12 on:** August 22, 2012, 06:34:57 PM »

2 prong, and when you unplug it, the you'll see 2 female contacts on harness side, and 2 male on the switch side. You jumper the 2 female contacts.

Bimmer805 · « **Reply #13 on:** August 23, 2012, 02:09:08 AM »

ok ill try that.

Bimmer805 · « **Reply #14 on:** August 24, 2012, 02:30:32 AM »

yipee it worked lol. so what do i do next for recharging?