PeachParts Mercedes-Benz Forum - Help 87300E Automatic Teperature Control Problems

I can't thank you all enough for your help but, thanks anyway.

Regarding oil usage: I recently took the car from NYC to Ottowa and back without a problem. It used 1 quart of oil for about 1500 miles rather than its previous average of 1 quart per 2000 miles. I have concluded that this is normal and does not require work. I check the coolant pressure (thanks for the correction Gilly) tank weekly and see no oily deposits on the underside of the pressure cap at all. This cap is new. There are however residual oily spots on the inside of the plastic pressure tank under the coolant. These spots stay the same, they do not go away or get worse. No oily deposits have risen above the coolant level. My mechanic says that everything looks good but, that I should keep an eye on the coolant and let him look at it frequently (he does not charge me for this 2 second monthly inspection).

Regarding the Automatic Climate Control problems: after I replaced the push-button-control-unit ("PBCU") with a remanufactured one from Phil the automatic climate control system worked fine for about 4 days before the original problem (see start of thread) came back. I double checked everthing, had the mechanic check the cabin temp. sensor, the auxillary fan motor and the vacum switches. These components worked. Just after these inspections, however, the automatic climate control system worked fine for about 3 hours under all settings, then reverted to the original problem. After all this my mechanic concluded that the remanufactured PBCU was at fault. So, pursuant to warranty, I've asked Phil to replace it. The new one should arrive tommorow.

I do have a couple of questions however. Rereading this thread I learned that the water pump's electrical draw could "blow" the PBCU. Is this so? I did not check the new water pump's electrical draw -- I assume that its draw is correct because the new pump came from Benz and all the work was done by my mechanic -- a very experienced MB specialist. Is this still a "big" concern?

Second, I was reading the recent posts in this forum and someone (91 300D) concluded that a short in the coolant temperature sensor (or the heater core temperature sensor) can also cause problems with the automatic temperature control system. (I do not know if my car has either of these). His problem was the reverse of mine. The system sent out a/c when the PBCU settings called for heat. Is this still a possibility for me when my system worked perfectly for while and then, before replacing any components, malfunctioned as previously described, and then worked perfectly for awhile before malfuncioning again? I do not think that a sensor short is my problem because, if that was the problem the system would malfunction all the time and not work perfectly sometimes as mine currently does.

It seems to me, given the intermittant nature of this problem that this problem is electrical, having to do with the PBCU. Given that the vacums and vents all work perfectly when they do and that the cabin temp sensor is new and the auxillary fan motor (which pulls air over that sensor) also works perfectly, I'm convinced that the PBCU is still at fault.

Any help is appreciated, but the moral of this story is, I believe, when the PBCU breaks do not replace it with a remanufactured unit, buy a new one: it's much safer.

After I lick this problem, next year I will install a performance cam, exhaust and euro lights (probably from Bekkers). Right now the car is obsidian black (the silly side piping removed) with clear cornering lights, new HD Bilsteins, shiny 15 hole wheels and new Continentals.

Marc