ACC Broken? - PeachParts Mercedes-Benz Forum

rmmagow · #1 11-03-2011, 01:28 PM

1985 300DT
The A/C doesn't work, never did since I've owned the car. I'm trying to figure out if my push button ACC is doing anything at all. I do realize there's a boatload of vacuum things involved here but read through and maybe give me some pointers about where to start. Vacuum thing in the car seem to work pretty much OK, locks lock and unlock, tranny shifts nice and 99% ot the time the engine will stop right away after turning it off.

My temp wheel works, get hotter and cooler moving it around. The Fan buttons work, hi-speed, middle speed (automatic?) and low. I don't seem to get a good volume of air when I push the defrost button, the vent on the driver's corner seems to blow the same volume of air no matter what button is pushed (vent flaps are broken). I generally leave the center button pushed in but pushing the other bottons doesn't do much of anything. The off button does shut the fan off.

The engine has trouble reaching 80C and might need a thermostat.

Is there anyway to definitively say the ACC control box is doing something? I am thinking to take it out and look at the solder connections. I'm still trying to figure out if in fact the flap control is doing anything. I am most interested in getting a good amout of heat to the front windshield during the winter weather to help thaw the car out in the ice. I don't drive it in heavy slushy type snow storms, but I do drive when it's cold and dry.
Pointer/links greatly appreciated.

leathermang · #2 11-03-2011, 02:15 PM

It sounds like a lot of your stuff IS working.... that is good...

I suggest replacing that thermostat first....as you seem to feel that you might be lacking in ' prime mover' heat for spreading to your windshield even if things were working perfectly... ....

The diagnostic section of the MB FSM ACC for just that dash unit is about 80 pages long... JUST the dash buttons...

Report back as to the change having the good thermostat in makes...

54dan · #3 11-04-2011, 02:27 PM

FWIW, I have the exact same issue on my '85 300TD. Air blows randomly but mostly out of the left-most vent. No change when the ACC buttons are switched.

I followed these instructions but ultimately found no real issues with the ACC:

Mercedes w123 Maintenance: Automatic Climate Control Unit Repair

I guess I ran out of inspiration at that point, but I suspect an issue with vacuum under the dash somewhere. ;|