A/C Fuse #20 Blowing? We've got your fixes!

[kenika65]

My # 20 30amp Fuse would blow if my a/c would be on for over 5-10min

  Then after installing another fuse, the a/c button would flicker and their would be a faint clicking sound from under the driver side dash.

 For the longest time I had my a/c clutch rigged to my fog light relay so I could turn the a/c on when needed.

 But its was time to fix it so I printed out a schematic for the a/c and started testing wires for pos and neg to make sure everything was getting the correct stuff.
 
 Long story short,

I unhooked the pressure switch located on the passenger front corner and tested the two wires at the connection.

The Blk/White wire is what gives power to the switch

The Blk/red wire showed to be a ground, which is wrong-- And when I gave power to it with a power probe It would blow the breaker in the power probe, meaning there is a short.

I then ohm it out to ground and sure enough it was shorted to ground somewhere.

After searching for a good long time I finally found the short.

It is on the driver side front corner, I had to remove the cover and unhook the wire straps.

The 220k wire harness wrap had flaked away and two wires had rubbed thought the paint causing a short.

The green arrow shows where it rubbed through the paint

The red arrow shows the Black/red A/C wire that had shorted

The yellow arrow shows a yellow wire that was also shorted( I dont know what it was for hummm)

[monty23psk]

good job on the find.

[1991 E30 M42]

A/C what is that, you dont need A/C or power steering

[kenika65]

Thanks and here in TX yes you do need A/C!

[Birdman16]

Great, that helps me out!!!

[stuv812]

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[xwill112x]

ahhh spammer!

fts!

[B318M42W]

ahhh spammer!

fts!

+1

[e9nine]

This same issue crept up to the top of my to-do list.

I randomly lost fuse 20 while the a/c was operating.

I replaced it and it popped again.

I swapped switches and it popped again.

I unplugged the Aux fan and depressed the switch and it popped again.

I then left the switch connected but didn't turn the a/c on and the fuse didn't pop.

With the switc still off, I jumped the Aux fan manually from the temperature switch on the radiator and both low and high speeds didn't pop the fuse.

I by-passed the switch and triggered the single probe to the a/c compressor and it runs and blows cold air without popping the fuse and the aux fan was jumped as well at both speeds.

Time to hunt and see where there's a short from the fusebox to the junction on the pass side as a quick visual inspection in the aforementioned area by the OP didn't reveal much (eugh).

I'll now tackle it in depth tonight by taking the bumper and valence off to get the best access to trace the harness after it exits the fuse box :eek: This is where bier comes handy! :cool:

[DesktopDave]

Good luck with that.  Keep us posted with what you find.

You might also want to test the diode inside the fusebox too.  IIRC it powers up the aux fan when the A/C button is pressed.  The thermo-switch on the rad uses a different side of the same circuit.

[e9nine]

After re-tracing all the wiring forward of the fusebox for any breaks and tracing the wires in the HVAC panel as well as the grounds, the issue isn't wiring related.

I seem to have an intermittent issue with the Evaporator Temperature Regulator. It seems to be inconsistent in operation and thus almost sent me on a wild goose chase as it would sometimes trip the fuse and other times not do so.
I swapped my spare one in (it's been swapped out before as someone marked it "good") but it's also popping the fuse. I might go borrow another one to further identify if it is the relay indeed or not. (wishful thinking eh)

The fuse no longer blows without the unit plugged in but the compressor will not engage or as it's controlled by this piece.

More to come later...

[e9nine]

A guided path to fuse 20 popping if the OP's solution isn't applicable (it wasn't in my case)

Items I had inspected/swapped

• Refrigerant switch (Open/closes & engages/disengages compressor)
• Blower Switch (Controls fan speed)
• Evaporator Switch (turns blower to speed 1, sends signal to Refrigerant switch and aux fan)
• ECU (increases idle to handle compressor)
• Aux fan diode (found on low speed aux fan wiring in fuse box)
• Compressor diode (mounted on compressor - 2 diff models exist for m42 cars)
• All wiring from the HVAC panel to the actual compressor
• A/C switch (Blue snow flake button and Recirc button work together off same wiring)
• Blower motor (Make sure you have 4 speeds)
• Main ground above brake pedal (make sure it's not frayed or lose)

I followed the wiring diagram and tested the whole circuit back-to-back. No real solution popped up as there were false victories and phantom moments.

I opted to swap the fan switch which operated fine at all speeds and didn't exhibit any signs of malfunction and it was only then that the whole circuit would operate fully. Hopefully this issue has been put to rest!
I have been using my a/c for 2 days now with no adverse effects.

For anyone who ever has this issue. There are so many items in the circuit associated with this fuse that you will have to simply test each thoroughly. Follow the ETM, be patient!

[DesktopDave]

The fan speed switch is potentially the culprit?  Odd.  Some e30 circuits are pretty convoluted, that's for sure.