87 300E climate control - PeachParts Mercedes-Benz Forum

retmil46 · #1 04-15-2007, 04:20 AM

Quote:

Originally Posted by Ken300D

Yes. I second Adam's suggestion that you resolder only the pushbutton switch terminals. They are pretty easy to find on the underside of the circuit board. Each switch has two rows of three terminals.

My primary problem symptoms were the fan running in the OFF position, and the AC compressor coming on in the OFF and ECONOMY positions.

The pushbuttons get a lot of stress normally, and a whole lot of stress from people who think violently pushing them in (while angry

) will somehow make the system act right. Once you get your pushbutton switch terminals resoldered - treat them very gently.

It is also worthwhile to resolder the three terminals that connect the round temperature setting dial if you can find them. They are in a row, adjacent to the wheel, on the circuit board.

By resoldering only switch terminals and the dial terminals, you avoid a lot of contact with more sensitive components that are probably still soldered in OK anyway. Its the control hardware terminals that get stressed and cold crack.

You may have other system issues, but this should fix the fan running in OFF.

Ken300D

Outstanding! Almost exactly the problem I have now. A/C will run in EC mode, will turn off when I press down and hold the EC button, kick back in as soon as I let off pressure. And half the time when I start the car, the blower motor will come on as soon as I put the key in Pos II to kick in the glow plugs, have to punch O to turn it off.

Already had the unit pulled out of the car, the bottom cover off, the temp dial removed, trying to figure out how to disassemble it further to get to the switches when I tumbled onto this thread. 3 AM so repairs will wait till tomorrow, but already sounds as if it's going to save me a lot of grief.

A few questions though -

This thread was originally talking about the CCU from an '87 300E. Same CCU in an '87 300DT?

Will a Radioshack ColdHeat soldering iron be adequate for this?

Would cleaning the circuit board and spraying it with a conformal coating after doing the resoldering be any help?

As far as the aux coolant pump - instead of having the pump powered off the CCU, would it be feasible to instead have the CCU powering a standard automotive 12V relay (using the wiring already installed to power the pump), with the pump powered thru the relay from another source (ie, straight off battery) with an applicable fuse in line?

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