94 124 ACC Climate Control Smoke & dead

[Bob Weir]

I strated the car on a 90deg very humid day. Off switch was engaged. I pushed the AC arrow down button, and a puff of white smoke came out of the center vent[s] and now its dead. No response to any direction buttons, fan speed or temp wheel. Fuse ok in main fuse box.

I pulled the control unit. Circuit board looks ok on one side. I released clips on face place, but it won't release completely and circuit board is partially secured in area near face plate. I'd like to release circuit board and inspect components on other side. How do I release circuit board? {8lb sledge & 3' crowbar?}

Could puff of smoke come from another component?

Suggestions appreciated...

Bob

[Rick76]

To remove the circuit board, you will need to pop the pushbuttons off and also remove the plastic pin that goes though the temperature adjustment potentiometer (couples the knob to the pot).

[Bob Weir]

Face plate has 2 tabs top and 2 tabs on bottom. Releasing these tabs allows faceplate to move about 3/16" from box containing electronics. Temp wheel is not affected by moving the face plate. Push buttons are very secure. Can prying on the face plate pop the buttons off?
Bob

[Chris W.]

I'm just at a bit of a loss how smoke possibly from the CCU could get up into the center vents. The vents are ducted while the CCU is just hung in the middle of the dash. If something fried in the CCU I would think some smoke might come out somewhere, but not necessarily from the vents.

On my car, one of the main power cables to the blower motor decided to fry itself quite close to the blower motor itself, causing mass quantities of smoke to come out the vents. All the vents. Scary quantities.... Not to mention that smell...

I was relieved to find it was only the cable and I spliced in a new section which has worked for a couple of years. Of course one has to take the blower motor out to do this, which is tedious in a 124.

Sorry to not be of much help!

Rgds,
Chris W.
'95 E300D

[Bob Weir]

Chris wrote


I guess I'll have to remove the plastic trim and jump the climate control fan motor to test it.

My thought as well. However, with all the comments regarding bad solder connections on the CCU, I thought it best to check it. My mother-in-law [previously an assembler for Allen Organ] found a few poorly solder connections, but nothing that would have caused the smoke.

So the question remains. What failed and produced the smoke?

Bob
PS Channel lock pliers work well to remove buttons.

[Bob Weir]

Summary
My mother-in-law examined the circuit board and didn't find any bad solder points. I replaced the strip fuse [$2.00 at MB dealer]. Fan motor tested ok [direct to battery]. I had a starter & altenator rebuilder check it and he said it's ok.

I tried Arthur Dalton's test posted 01-19-2006, 08:16
< You check for power at the 3 prong conector behind the booster. Red/blk is 12v power and y/blk is variable power [ 2-8v] for regulator trigger. If both are good, ground blu wire at regulator to complete the switched ground circuit. If blower works, reg is bad. >
but I don't think I did the correctly.

I removed the regulator and added more dielectric grease and noticed the original grease is "white" in color. Maybe this is what produced the white puff of smoke?

It functions properly, but today is cool & dry not the hot humid weather when it failed.

So the questions remain; what caused the white puff of smoke, and the blown strip fuse?

Bob