Exploding A/C temp regulator

[IanJ]

Trying to diagnose the A/C in my '85 300D.

Installed a known working temp regulator (from my other car!) in the bad car. As soon as I applied power.... I heard a loud POP from the temp regulator box! (Now this box rattles just like the one that I pulled out did!)

Anybody have any idea what could cause the temp regulator box to blow like that?

I'm afraid I've let the magic smoke out of too many of these boxes!

[Larry Delor]

I've read that non-functioning aux. water pumps can make them go kaplooie.

[IanJ]

Actually, I had heard the same thing.... therefore I had already had the aux. water pump unplugged from previous troubleshooting before I tried the other temp. regulator.

Could a bad blower motor do the same thing? I can make the blower motor run though by jumpering it.

[Jeremy5848]

By "temp regulator" you mean the thing in the dash with the pushbuttons, the ACC? I ask because I'm not as familiar as I'd like to be with the ACC system in our cars. My unit had a bunch of fried traces and did not work completely. It came to me in that condition. I wired around the problems and resoldered everything (like the cruise control cure) and now everything works.

My guess would be a short somewhere, as Larry has already suggested. The ACC doesn't have many electronic things, mostly a bunch of small relays. Possibly one of them went pop. I would imagine that they control the monovalve, aux water pump, compressor, and blower motor. There is another controller behind the passenger side dash, or so I have read, plus a box of dropping resistors for the fan, on the passenger side inner fender. If you can open the thing up and figure out what went "pop," I may be able to help more with the diagnosis.

Jeremy

[IanJ]

Originally Posted by Jeremy5848

By "temp regulator" you mean the thing in the dash with the pushbuttons, the ACC?

No, I've actually already put a different ACC pushbutton box in there. The temp regulator box I'm talking about is the silver Bosch box back behind the glovebox. The other black box behind the glove box is the blower regulator box (already replaced it as well!) The resistor box under the hood also appears in good shape and is not shorted to ground.

After further investigation... the temp regulator box that went POP still appears to work in my other car. I did pull the box open though to see what happened inside. There are a series of large metal plates standing up across the back of the circuit board. Each plate comes from a small plastic covered block on the board. The black plastic covering that block popped off at one of the plates... but nothing else appears to be fried.

Anybody know what these plates are for?

I guess I got the power shut off to it quick enough!

[OMEGAMAN]

Go here http://mb.braingears.com/ and you can down load the factory manual for the climate control.
Also go to your public library they may have a good manual selection. Mitchell Manuals are in lots of libraries and are sometimes easier to use than the factory manuals because they are re written, even the wiring diagrams.

[SD Blue]

Originally Posted by IanJ

.......... There are a series of large metal plates standing up across the back of the circuit board. Each plate comes from a small plastic covered block on the board. The black plastic covering that block popped off at one of the plates... but nothing else appears to be fried.

Anybody know what these plates are for?

I guess I got the power shut off to it quick enough!

I'm not absolutely positive if this is what you are describing. But in nearly all electronics assemblies with large metal "plates", these are used as heat sinks for heavier current draw. It sounds as if you have a short that can fry things. Do you have a multimeter and know how to use it? (Not an insult, just trying to determine your experience with electronics.) I would check the pins at the connector for a short. Let me know if you need help.

From everything you mention, I am wondering if you got ahold of the wrong ACC controller for your car.