1980 300SD Climate Control Issues
 

Fan only works on high on defrost as it should since it bypasses everything I think. A/C comes on at first cold, then as engine warms up hot air blows as it should (it's on defrost). New compressor comes on, A/C charge is fine, new pressure switch, new temp switch, new expansion valve.
No other controls work.
Is this climate control module under hood? Or could it be button switches on dash? Or maybe vacuum problems (wouldn't be surprised at that)? Anyone know where to begin testing what and how with amp/voltmeter and Mityvac pump? Suggestions would be much appreciated.

1980 300SD
1982 380SL
1979 300CD
1997 C220

Have you tryed www.mb.braingears.com this is service manuals you may view. I have a simular problem with my 77 300 D. I have a slow speed with auto-low, and a little more air with auto-hi. It seems like the defrost mode is a little more speed on the blower, but hard to say. Give this a try, and good luck.

Look at the black monstrosity under the hood....if you find any cracks on it its bad.....odds are its bad anyway. there is also an amp behing the glove box...one will usually smoke the other. You will need a manual even if its the CD version....good luck finding a hardcopy Climate control manual...they are as rare as hens teeth. THe Chiltons will be worthless.

Steaky.skinnerbox.org used to have online manual but they went bye-bye recently. There is an alternative place but I don't remember what it is.

Expect an expensive fix...rebuilt ACC servos about $350 and amp about $100

if you buy one buy the other....

A/C followup a neverending saga....
 

OK.... I checked various vacuum tubes once I was able to follow some of the color switches (I do have a W116 manual on CD) that were apparently added on at a later date. I was never able to find the vacuum resevoir which I think is supposed to be behind the driver side wheel well. I know there is another one in the trunk but I'm not sure it has anything to do with this issue.

I unplugged the control switch behind the dash a checked vacuuum there at the tubes. They all seemed to hold a vacuum and I could hear some switches click.

The upshot was I connected the black vacuum tube to the tube that controlled the side flaps (hillbilly rigged it)and got both a/c and heat (bi-level and auto high and low, though the fan may run at only one setting and never cut off) depending on the temperature dial setting. On this setting it appears that the A/C compressor runs all the time, which I think is probably correct.

Mt question is: Do I have a faulty vacuum switch on the dash?? That's is my best quess. Any other suggestions? Is such a dash swith available anywhere, new or used?

Thanks in advence for any assistance.

Make sure the inline fuse buried in the fuse box (it's not one of the ones you can see) hasn't blown. Next most likely is the ACC, last would be the amp.

Good luck. I never could have serviced my ACC on my 80 450SEl without the manual. I just put it up for sale in the Parts forum.

fuses in fuse box
 

There are 2 in-line fuses in the fuse box. One has a regular MB fuse in it (I think it's 25 amp) and the other in-line fuse holder is empty. What is that one supposed to be for?
Thanks.

One is for the radio and the other is for the a/c ..... per my Mercedes Benz Electrical Troubleshooting Guide that is for sale :sun_smile

I don't recall the fuse size for either but if memeory serves it is on the paper in the lid of the fuse box.