A/C compressor runs sometimes

[ACC2]

Would anybody be able to point me in the right direction of why my 1980 300SD with ACC2 runs the compressor only sometimes. My servo and amp have been removed and replace with the mercedesfix.com upgrade, but as I understand this is not involved with compressor operation. I'm trying to figure out exactly how the compressor is told to engage.

Thanks

[daantjie]

From my limited knowledge on this if the system has too low pressure then the pressure switch will make the compressor not kick in.

[ACC2]

From my limited knowledge on this if the system has too low pressure then the pressure switch will make the compressor not kick in.

I recently had the system serviced though. It also works randomly and blows cold when it does...

[UTn_boy]

I still echo what I said on the restorer's guild page.  The only other thing I'd check is the a/c compressor relay.  Even so, I still think you have a vacuum leak causing one or both of the vacuum switches not to work properly.  You had asked about a schematic, and that is here in the library.  None of us can pinpoint what your exact problem is from afar.  You're going to have to do a lot of the diagnosing and testing yourself.  You need to confirm that vacuum on the climate control system is holding steady at idle and when accelerating, and you'll have to confirm the electrical part is in good order.  But again, because you have the aftermarket set up on your car things are much more complex and unknown now, and a large majority of the factory schematics will not apply.  If I were you I'd contact the people you bought the aftermarket system from and ask them for a schematic so you can properly and easily test the system without a bunch of guess work. 

[ACC2]

I still echo what I said on the restorer's guild page.  The only other thing I'd check is the a/c compressor relay.  Even so, I still think you have a vacuum leak causing one or both of the vacuum switches not to work properly.  You had asked about a schematic, and that is here in the library.  None of us can pinpoint what your exact problem is from afar.  You're going to have to do a lot of the diagnosing and testing yourself.  You need to confirm that vacuum on the climate control system is holding steady at idle and when accelerating, and you'll have to confirm the electrical part is in good order.  But again, because you have the aftermarket set up on your car things are much more complex and unknown now, and a large majority of the factory schematics will not apply.  If I were you I'd contact the people you bought the aftermarket system from and ask them for a schematic so you can properly and easily test the system without a bunch of guess work.

Where is the A/C compressor relay located?

I can confirm the system is holding vacuum well, I used a gauge/pump and amazingly the system does not appear to leak at all.

-Apologies. I'm going through the manual now. Thanks!

[UTn_boy]

Alright, then now you need to test the vacuum switches to ensure that the electrical contacts are closing circuit when vacuum is applied. 

They ACC systems was designed with a slow bleed down (the coiled up green wire that plugs into a rubber vacuum line connector behind/under the glove box) so after the engine is turned off the ACC vacuum system should loose all or most of its vacuum within 10-30 minutes. 

As far as the a/c relay location......I have no idea.  It'll be in one of three places.  In the fuse box, next to the vacuum switches behind the glove box (early), behind where the top right side of the console meets the lower dash pad (late), or behind the left kick panel in the left floor pan area (remove the panel behind the hood release handle).  Again, the location is more than likely shown in the technical manual located in the library on this very forum.