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DISCUSSION => Electrical => Topic started by: Bimmer805 on August 19, 2012, 09:37:30 PM

Title: A/C compressor wont engage
Post by: 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:(
Title: A/C compressor wont engage
Post by: DesktopDave 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.
Title: A/C compressor wont engage
Post by: Bimmer805 on August 20, 2012, 10:31:59 AM: Oh ok I check for power there and I didn't get anything
Title: A/C compressor wont engage
Post by: Bimmer805 on August 20, 2012, 04:39:03 PM: i have check for power on the pressure switch and im getting no readings
Title: A/C compressor wont engage
Post by: DesktopDave 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.
Title: A/C compressor wont engage
Post by: DesktopDave 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.
Title: A/C compressor wont engage
Post by: Bimmer805 on August 20, 2012, 10:27:48 PM: I push the snowflake button and the aux fan does come on
Title: A/C compressor wont engage
Post by: DanOKC 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.
Title: A/C compressor wont engage
Post by: Bimmer805 on August 21, 2012, 01:43:24 AM: how do i go about jumping the terminals?
Title: A/C compressor wont engage
Post by: DesktopDave 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...
Title: A/C compressor wont engage
Post by: DanOKC 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.
Title: A/C compressor wont engage
Post by: Bimmer805 on August 22, 2012, 04:58:50 PM: theres one like a three prong and theres one with a two prong which is it?
Title: A/C compressor wont engage
Post by: DanOKC 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.
Title: A/C compressor wont engage
Post by: Bimmer805 on August 23, 2012, 02:09:08 AM: ok ill try that.
Title: A/C compressor wont engage
Post by: Bimmer805 on August 24, 2012, 02:30:32 AM: yipee it worked lol. so what do i do next for recharging?
Title: A/C compressor wont engage
Post by: DanOKC on August 26, 2012, 12:56:08 AM: Well, if you don't have any experience at recharging AC, find a shop or mechanic who will
recharge with R12. They will pull a vacuum on the system, make sure it holds, and add the proper amount of R12, and monitor the high and low pressure with a manifold gauge and monitor vent temps and make sure the system is cooling properly. Y

Other options are pay more money for R134 conversion or find a shop or mechanic that is agreeable to use a blend like Freeze12. You can find R12 cans and Freeze12 on ebay.
Title: A/C compressor wont engage
Post by: Bimmer805 on August 26, 2012, 01:33:20 AM: how much would a shop charge me for recharging?
Title: A/C compressor wont engage
Post by: ak96ss on August 26, 2012, 06:34:45 AM: Just as an aside, I posted an updated version of the ETM here (http://www.m42club.com/forums/showthread.php?t=7748) a few years ago, which includes many of the missing pages... ;)
Title: A/C compressor wont engage
Post by: DanOKC on August 26, 2012, 07:39:20 PM: Quote from: Bimmer805;115198
how much would a shop charge me for recharging?

I don't know, never paid for that. My dad was an HVAC tech when I was young, and I picked up enough that I service my own AC for home, auto, etc...

It could probably vary wildly if you just call or go into shops & tell them what you have & what you want. Most might push for R134 conversion. The one you want it the guy who says, "yea we can do R12", IMO, but they may be hard to find.