troubleshooting ac - PeachParts Mercedes-Benz Forum

bellyboy · #1 08-09-2007, 04:27 PM

83 300sd

been searching around.

i believe there is a few issues going on. was getting heat mixed in with the ac changed mono valve seems to be better. now i getting no fan in the cabin. i would appreciate suggestions on how to troubleshoot whether it is blower, regulator, vacuum etc. your thoughts are appreciated on where you would go next. have noticed my idle is slightly rougher right around the same time this no cabin air blowing started.

thanks

#2 08-09-2007, 04:32 PM

I would check the fuses first, I don't remember the number of the AC/blower fuse but I've had it burn out for no apparent reason.

bellyboy · #3 08-09-2007, 04:39 PM

those are good.

when it was intermittenly working it would go on a few minutes after the button was pushed

#4 08-09-2007, 04:44 PM

Quote:

Originally Posted by bellyboy

those are good.

when it was intermittenly working it would go on a few minutes after the button was pushed

That sounds a lot like the ACC (pushbutton unit) is acting up. They often start by failing intermittently, sometimes just the defrost button will work or you can make the whole thing work if you push the defrost button first.

rrgrassi · #5 08-09-2007, 04:45 PM

HAve you checked to make sure the aux water pump has not locked up? If it is not fused, it has been known to take the CCU with it. Also, check the CCU. Some have had good luch resoldering all the connections.

bellyboy · #6 08-09-2007, 04:57 PM

hmm.. if i only knew how to troublshoot these

#7 08-09-2007, 05:08 PM

Good question, most folks seem to "troubleshoot" them by either resoldering them or replacing them. When I got sick of mine acting up, I replaced it with a rebuilt unit. There may be some info on the forum for troubleshooting.

bellyboy · #8 08-09-2007, 06:01 PM

going to place some leads on the blower if it works it is the ccu if it doesnt it is the blower

#9 08-09-2007, 06:07 PM

Quote:

Originally Posted by bellyboy

going to place some leads on the blower if it works it is the ccu if it doesnt it is the blower

That should tell you if the blower is good, but there are still other possible causes (although it's usually the CCU).

bellyboy · #10 08-09-2007, 08:06 PM

Quote:

Originally Posted by Craig

but there are still other possible causes (although it's usually the CCU).

how true

tested it seems to work variably. i would agree it is both the ccu and motor,brushes, accumalator. when i hooked it should work variably(no constant speed) if it was just the motor

#11 08-09-2007, 08:13 PM

Unfortunately, a bad blower motor (as well as a bad aux pump) can contribute to the demise of the CCU. I ended up replacing the CCU and the motor at the same time (the motor was noisy and the CCU was toast).