AC problem no power to fuse #20

[Skoobeesnak]

WIth the hotter weather coming on I couldn't stand the thought of another long hot summer with my black on black '87 325is so I took it to a shop that specializes in automotive AC. Long story short, he ended up replacing the compressor converting it over to 134a and recharging it to work. The problem is that the AC does not turn on the compressor but the switch inside does turn on and light up. This is what I have found so far.

1- No power to fuse 20 which from what I understand engages the compressor.
2- When the old unit went out it fried the circuit board behind the switch which I have since replaced and now the button does turn on.
3- When the AC guy tried to get the old compressor to take a charge the clutch was fried which heated up the wire he used to short or force the compressor to engage. It was at this point he figured out a new compressor was needed since it was only $80 more than a clutch alone.

I am at a loss on what my next troubleshooting step would be. I have checked the power going to fuse 20 and I don't get any voltage. Please help if you can.

Thanks,

[HarryPotter]

If your switches are lighting up fuse 20 is definitely getting power. Fuse 20 powers almost all of the HVAC stuff the only thing it doesn't power is the aux fan. Power comes off of fuse 20 and into the the dash to the a/c button, off the back of the button it goes to the compressor. Maybe the button is bad check that to see if it works.

[Skoobeesnak]

Bad thermostat-switch

One other thing, it appears that my aux fan sensor is dead. I was able to test it by shorting the high and low speed settings on the switch as outlined in the Bentley manual and it worked on both high and low so I need a new 3 prong temperature sensor on the radiator. Would that cause the AC to not kick on?

[HarryPotter]

One other thing, it appears that my aux fan sensor is dead. I was able to test it by shorting the high and low speed settings on the switch as outlined in the Bentley manual and it worked on both high and low so I need a new 3 prong temperature sensor on the radiator. Would that cause the AC to not kick on?

I am not 100% sure but it might be an issue. I know mine didn't work so I hotwired the low speed to come on 24/7 when the cars in the on or running position. That might definitely be an issue.

[Skoobeesnak]

If your switches are lighting up fuse 20 is definitely getting power. Fuse 20 powers almost all of the HVAC stuff the only thing it doesn't power is the aux fan. Power comes off of fuse 20 and into the the dash to the a/c button, off the back of the button it goes to the compressor. Maybe the button is bad check that to see if it works.

This is odd because I pulled the fuse out of 20 and put my multi-meter on and didn't get any voltage at all. Maybe it has to be running or have the key on in that position to provide power. Can anyone else confirm this?

[HarryPotter]

Key needs to be in the on position.

[Skoobeesnak]

Bump

OK I checked the fuse with the car running and with the AC switched turned on and I am still not getting any voltage reading at fuse 20. Any idea how this is possible or where I should go next? I am willing to tear into the wiring harness but where should I look? Trace it back from the compressor?

[jlevie]

Have you checked the wiring diagrams (http://wedophones.com/BMWManualsLead.htm) to see how the circuit works? That will tell you where to check.

[Kershaw]

have you tried to jump the k5 (or is k7?) unloader relay to see if that will turn it on?

[Skoobeesnak]

have you tried to jump the k5 (or is k7?) unloader relay to see if that will turn it on?

I am not sure which pins to jumper on the relays or else I would give this a shot.

I was looking at the wiring diagram and it mentions a 2 amp inline fuse in the circuit near the water shutoff solenoid mentioned on the wiring diagrams but I am not sure where this fuse or the solenoid is located. Can anyone tell me where it is or show a picture of it?

[603Racing]

Reviving this thread, I'm having the same issues and would like to know if there was a resolution?

[SmokeE30]

maybe a previous owner has switched to another terminal on the fuse block to provide power to the hvac

[jlevie]

Reviving this thread, I'm having the same issues and would like to know if there was a resolution?

Use the wiring diagrams from the link posted above to find out why there is no power at fuse 20.

[603Racing]

I'm pretty sure at this point that I have a wiring issue. I have power at fuse 20, which is a 30 amp fuse. My blower fan works, my AC button lights up and sets the car to high idle. But I'm still not getting power to the AC components in the front of the car. If I jump the compressor it engages, but it does not work as it should with the button.

[rtwaits]

I have a similar problem. I havent checked at the fuse box for power, but the 12v wire to the compressor has no power. I have only started to try to trace the wiring. The light in the switch goes on. The passenger compartment blower fan goes on. the Auxilliary cooling fan in front of th engine does NOT go on. Looking at the wiring diagram, there is a High and Low pressure cut out switch - Im guessing as our cars are old, there is no pressure because there is no freon? The test is to look in the sight glass, but a bit difficult if the compressor doesnt go on
Ideas?