Smoked climate box - PeachParts Mercedes-Benz Forum

kafer65 · #1 10-30-2006, 09:48 AM

Been having problems with the HVAC on my '83 300td. All the pods check out except for the dreaded center vent pod and its a slow leak. AC is working and a get heat too but none of the pods ever move. I took the pushbotton box out and apart and whatyaknow its been real hot on the circuit board at one point. The fried circuit seems to have something to do with one of the copper wound relay switches associated with the airconditioning maybe. I have a lead on a used replacement but would this unit be consided junk or repairable?

SD Blue · #2 10-30-2006, 10:02 AM

I have not seen the fried circuit board, but have heard reports of an aux. water pump causing this. You might try some jumper wires direct to the batt. and aux. pump to see if it turns over like it should. Some have suggested installing an inline fuse, on the pump wiring, to prevent this.

If you have some type of electronics repair place nearby, they may take a look at it and see if it is considered repairable. (Or post some very definitive photos.)

Jeremy5848 · #3 10-30-2006, 11:06 AM

You should be able to run wires to replace the fried traces. That is actually a very common fix in the printed circuit board world. My ACC controller has several such jumpers dating back to the time the PM fried the board when the aux water pump froze and drew too much current. I cleaned up the board and put a fuse in the pump lead. Somewhere I have pictures, maybe already posted. I'll do a search and update this evening.

Jeremy

kafer65 · #4 10-30-2006, 02:45 PM

Well flip! Another thing to fix! I read post from pelagro that mentioned pins 9 and 10. Pin #10 was the one on mine thats fried. It does, however, have continuity across it. I'll check the aux. cooling pump and put a 1 amp fuse in. Any ideas on where to look on the circuit board that could get the switch valves that direct the vacuum working? Is there a way to test them?

SD Blue · #5 10-31-2006, 10:02 AM

Myself, and many others, have reported that usually the problem is with the solder connections along the edges of the main circuit board where it connects the two side boards. Over time the solder joints develop cracks and you get a lot of intermittent operation. Resolder those joints and see what you have from there.

kafer65 · #6 11-01-2006, 09:46 AM

Aux cooling pump is DOA. No continuity. No go jumpering from the bat-tree. Its going to fry anything that tries to us it so could I just unplug it until I can bypass or fix it? I'd like to get the center vents working and the dash back in and save the ACP for later.

SD Blue · #7 11-01-2006, 09:52 AM

Sure you can unplug it. From my understanding, it is mainly for heat while idling. If you do a search for "rebuild" and "aux pump", I believe it was Carrameow who had some photos and info on how to.

mplafleur · #8 11-02-2006, 06:50 AM

The aux heat pump is attached to the monovalve assembly at the bottom-right. The connector for it is clipped to a bracket on the left side of the monovalve assembly, next to the battery.

kafer65 · #9 11-08-2006, 03:28 PM

I resoldered some of the circuits relating to the relays since they looked cracked. All circuits I tested were good. Disconnected Aux. pump plug and comfirmed that many of the circuits are working. I had some vacuum lines that had been plugged shut that were in very discrete places around the vacuum manifold that needed opening up. I have all pods showing activating now. Center vent pod will need replacement or manual bypass but I see the light at the end of the tunnel!