Auxillary fan wiring problem

[DaveSmed]

The purpose of the diode is to prevent voltage from backfeeding through the A/C switch from the temp switch- It makes it so the A/C doesn't kick on when you overheat.

That could be missing completely, and you should still see 12v at the temp switch on the rad.

Do your power windows and HVAC blower work?

[emi325i]

While diagnosing my aux fan problem, I found a molten mess inside the fuse box. You should check that just to make sure.

[bmwpower]

The purpose of the diode is to prevent voltage from backfeeding through the A/C switch from the temp switch- It makes it so the A/C doesn't kick on when you overheat.

That could be missing completely, and you should still see 12v at the temp switch on the rad.

Do your power windows and HVAC blower work?

Good to know.

Need to retest those components...will get back to you.

While diagnosing my aux fan problem, I found a molten mess inside the fuse box. You should check that just to make sure.

Uh-oh. I assume you had to take the fuse box apart to see the mess. I've never done more than pop the clear cover.

[emi325i]

Good to know.

Uh-oh. I assume you had to take the fuse box apart to see the mess. I've never done more than pop the clear cover.

Yes, remove all fuses and relays, and take out the screws. Comes apart pretty easy.

[bmwpower]

Alright.

Went out and checked things again.

Installed the window switches and tried the windows. Didn't work. Then I realized the circuit breaker was not installed. Installed the breaker and the windows worked.

Then I tried the A/C button - nothing.
Defrost - nothing
Fan?? - nothing

All worked the other day when I tested. I didn't try uninstalling all the window switches and the breaker to see if the HVAC would work.

Carpet and interior is out. Anything on the interior would cause this? Nothing crazy happening on the interior, just gutting stuff.

Time to find the HVAC diagram...

[DaveSmed]

Alright.

Went out and checked things again.

Installed the window switches and tried the windows. Didn't work. Then I realized the circuit breaker was not installed. Installed the breaker and the windows worked.

Then I tried the A/C button - nothing.
Defrost - nothing
Fan?? - nothing

All worked the other day when I tested. I didn't try uninstalling all the window switches and the breaker to see if the HVAC would work.

Carpet and interior is out. Anything on the interior would cause this? Nothing crazy happening on the interior, just gutting stuff.

Time to find the HVAC diagram...

Hold that thought. Check the top of the posted diagram.

Take a real good look at relay K7... Which controls power to the radiator switch and HVAC among other things.

[bmwpower]

Hold that thought. Check the top of the posted diagram.

Take a real good look at relay K7... Which controls power to the radiator switch and HVAC among other things.

Ok...Lemme go out and look at it.

Any way to test it other than swapping it out? I have an 87 325i fusebox. Checking realoem to see if it's the same....

[kishg]

Ok...Lemme go out and look at it.

Any way to test it other than swapping it out? I have an 87 325i fusebox. Checking realoem to see if it's the same....

should be the same. do you have a bentley, i seem to recall there was a test procedure in there. will check in 5m.

[bmwpower]

I have a Bentley. Checked but didn't see anything just now.

Well I'm out here and it looks like fuse #20 (30A) blew, how I have no idea. Maybe when I was restesting things tonight. Threw a 20A in there for now (note to self ... buy more 30A fuses).

A/C works now.

Retesting...

[bmwpower]

Fixed it

Figured it out.

Fuse #19 (7.5A) was not TIGHTLY seated in the fuse box. Took it out again...hmmm...seems loose. One of the connectors in the fuse slot was not contacting one pole of the fuse completely - hence no power to thermo switch connector. I took a small pick and carefully moved the connector inside the fuse slot closer together. Viola!

Thanks to all who helped. Pissed off I didn't notice that earlier, but the fuse wasn't blown and it seemed ok going in/out the fuse slot.

[DaveSmed]

Nice, good find.

Gotta love how a few things acting up can make it look like one thing...

[bmwpower]

Nice, good find.

Gotta love how a few things acting up can make it look like one thing...

Yea, go figure. And never had a problem with a fuse slot before. Won't overlook it anymore.

Thanks....

[bmwpower]

In this case get an 82C thermos switch from BavAuto and a 30A generic relay and fuse from any auto parts house. Tap power for the fan from the power distribution block on the firewall, run it through the fuse and then to the relay. I recommend installing a switch to allow manual engagement of the fan.

Using the existing thermo switch isn't a great idea as its low limit is 91C and the high limit is 99C. That's quite a bit higher than you want the fan to come on if deleting the engine fan.

You have a part number for that 82C switch?

[JeepJockey]

I have a Bentley. Checked but didn't see anything just now.

Well I'm out here and it looks like fuse #20 (30A) blew, how I have no idea. Maybe when I was restesting things tonight. Threw a 20A in there for now (note to self ... buy more 30A fuses).

A/C works now.

Retesting...

Digging this thread up to ask about this post regarding fuse #20. Fuse #20 is blown on my car and putting another 30amp in it immediately blew when the A/C switch was depressed. I am not getting any voltage to the Blk/Rd wire going to the A/C clutch when the A/C switch is on (blue light is lit). If fuse #20 is blown will it prevent voltage at this wire? This post seems to answer this question with a "yes" but just making sure.

Thanks

[scabzzzz]

Bump.