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HELP!!!!!!!!! Aux Fans/AC Compressor not moving

634 views 3 replies 3 participants last post by  BlackVinDiesel 
#1 ·
Hello everyone! I'm a new member here, however I've been coming to this site for years, & reading threads that others have posted for information. The majority of my questions (if not all) have been answered from the knowledge posted on this forum. However, I've finally ran into a problem that I am not familiar with myself, and I'm looking for some guidance as to what to do next.

In January, I purchased a 96 S500. I managed to get it for a good price, and for the most part, nearly everything worked in it when I checked it out. Some minor work had been done to it, but nothing too crazy. But I will tell you my story of how this all started.

I recently had it painted, and the day I picked it up, I was on my way to the DMV to swap over my custom plates from another car. When I reached the DMV, I got out & heard this loud HISS, I walked to the passenger side & noticed that there was coolant everywhere. Seemed that the brass collar on the coolant bottle finally split front the bottle housing, causing it to leak. I called a family member who brought some water, filled the car, and got home before it could over heated. We then went to the junkyard & swapped out a coolant bottle from another w140 they had in the yard. Put it in, no problems. Drove to a party later that night, came home, & I noticed my car was approaching red on thermostat. Pulled in the driveway & smoke started to develop fast. I shut the car off, and got out to inspect, noticed a pin hole leak coming from in the radiator, and the cap was leaking on the coolant bottle I swapped out. :(

At that time, I decided to change out most of the coolant system, since I didn't know when the last time it had been done, & the car has 146k. Ordered an updated coolant bottle (fitted with the plastic cap), a radiator, thermostat, level sensor, and some hoses. Put the new parts in, inspected the hoses, and they all looked good except for one. Changed that, flushed the system, put in new G-05 coolant, ran the car, took it on a test run around my neighborhood... no leaks. But for some odd reason, I noticed that the car was still running hot (almost reaching 120 C). I returned home, checked my coolant level, & it was still full, so this was confusing. :confused: Then I noticed something: neither of my aux fans in the front had kicked on since I started the car. So I read up on them, and saw that the ECT sensor is supposed to actuate them once it reaches a certain level. Ordered a new one, and replaced it: nothing. So I thought maybe the fans were bad. I read up how to jumpstart them from the Climate control module inside the car, tried it and... nothing. It was also at this time I noticed that my A/C wasn't working at all. Inspected the AC compressor, and the clutch will not move when the car is running (there is refrigerant in the system). So I figure maybe the 2 are connected.

So, I ran a continuity test, was getting continuity from both fan assemblies, but nothing from the harness connectors. So I thought, well maybe it's the fan module itself. Changed that out with a fairly used one from another Mercedes, nothing. I Managed to talk to a friend that is a tech at MB of Buffalo, and explained to him everything that has happened, & he told me the last thing to inspect before changing the compressor, would be the Climate Control module itself. This is where it gets interesting. I found one at the yard from a w210. I replaced mine with it, and still no AC, still couldn't jumpstart my fans with the "hold the Auto buttons for 10 secs" trick. Now, my father owns a w208 CLK... I thought what the hell, lets swap those and see what happens. I took the climate box from that, and put it into my w140, and I was able to jumpstart the aux fans with it! Go figure! However, I still couldn't get the compressor clutch to actuate.

So I am currently at the end of my rope as to what to do. I am thinking that I'm going to have to get a another climate box, still change out the compressor, flush the system, and replace the refrigerant. This will be something that I will have a shop do probably, but I was wondering if anyone else has dealt with this at all. I went to one shop that specialized in A/C work, & one that specializes in fixing german cars, but they were talking about chewing me a new ass just to diagnose the issue! Any advice as to what I should do next? Summer is here & it's getting hot! Thanks in advance guys! Cheers!
 
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#2 ·
Well at least you did some thorough troubleshooting there!

One suggestion -- the climate control box on other Mercedes models of the same era may look identical to the one in the W140, but I'm almost positive the systems function differently and the W140 box is unique. Units from other cars may be compatible with some functions, but not others.

Before you go and buy a new AC compressor and start shelling out to a repair shop for diagnostics, my suggestion would be to first source a new W140-specific climate control unit and see if that restores functionality. I'm sure you can find one on Ebay for relatively cheap.

Worst case scenario you're back to square one, but at least you'll have one component replaced.
 
#4 ·
Thanks you guys for the insight. I managed to source a fairly used climate control module from a trusted salvage yard in town. Managed to get it in the car & still had no progress in solving this mystery. So I finally caved and drove around town, and found a good mechanic that specializes in german cars. I explained the story to him, and he was able to find out what the problem was. The AUX Fans weren't firing because the grounds were messed up, and the AC compressor is clogged, so it needs to be replaced (will worry about this in the spring, as it is about to get cold). So he rewired the, and also, the reason the car was overheating: the damn fan clutch on the main fan was shot. He had one laying around in the shop so he replaced it, and boom! Car runs great now!
 
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