AC intermittent - PeachParts Mercedes-Benz Forum

odie · #1 07-20-2009, 12:19 PM

Damn AC is going out. plenty of freon the best i can tell. I put a guage on the low side fitting with the car off and it jumped to close to 200 psi so there is plenty of pressure/freon in the system. It just blows ambient and occasionally the AC will kick on for a few minutes. then off again for a long time.

I'm guessing a wiring problem or failing sensor. I've done some searches and seems this KLIMA relay thing is a possibility or some temp cut-out switches? So many wires and stuff on these cars. The compressor appears to have something like 5 wires going to it? I'm used to just one wire for the clutch.

Will start tracing wires, checking connections and looking for relays that I have no clue where they are...wish me luck and offer any advise...it's 100 plus in South Texas and I really don't want to take it in the shorts from a shop.

rrgrassi · #2 07-20-2009, 02:30 PM

Is the compressor randomly engaging/dis engaging? HAve you tried juming the compressor to see if it stays engaged? If it stays, the pressure switch could be the problem.

Klima can cause that, as can a failing pressure switch, or a failing compressor clutch.

Check all the connections.

My car does not have a Klima, so I'm just throwing out some basic stuff.

ds190 · #3 07-20-2009, 09:11 PM

"I put a guage on the low side fitting with the car off and it jumped to close to 200 psi so there is plenty of pressure/freon in the system."

Whaaa??

Low side pressures are indeed low, like 20-50 psi depending. High side pressures are indeed high, like 160-190 psi or so.

You've got a clear problem if you've got 200 psi low side. Check for overcharged system or bad compressor.

erik · #4 07-20-2009, 10:08 PM

Is your engine tach working fine? not sure what year MB put in the comparator circuit but if it's also intermittent, that could cause the A/C to be intermittent due to the comparator circuit comparing compressor speed to engine speed. If there is >10% diff it may think the compressor is stalling/frozen and turn off the clutch.

Cheers!
Erik
No, I'm not a MB mechanic but I did sleep at a.....
you get the picture, your mileage may vary

odie · #5 07-22-2009, 05:27 PM

i don't recall the pressure but it was way high. and the car was not running so i would think the pressure evens out through the whole system when static. I have not added any freon, it's been running cold and great for months, just now stopped.

by intermitent i mean it does not work at all then suddenly while driving it decides to cool down for a while, then quit again. it's not the compressor cycling a bunch. it will not work for days or several short trips, then suddenly work when i get in the car and drive to the store or something.

my guess is a loose connection under the hood somewhere, barely making contact, depending on bumps in the road...but that's just a guess

odie · #6 07-22-2009, 05:29 PM

decided to work today. it's like i'm afraid to mess with the wires if it's cooling. and jiggling the different wires and connectors when it's not does not seem to do anything.