Another Climate Control Problem - PeachParts Mercedes-Benz Forum

chrislk02 · #1 08-06-2007, 03:51 PM

I have a 1985 Mercedes 190E with about 150,000 miles on it. The problem is with the climate control system - The air temperature from the vents remains the same no matter what temperature I set the dial to. If i set it to hot, it does not come out as hot as I would expect heated air too, set at cold, it is way to warm for Airconditioned air. It appears that all vent control work (I.E., middle vents, side vents, floor vents and defrost). I have read alot of threads on climate control problems and I found none that were described as this one. Any suggestions?

pwogaman · #2 08-06-2007, 03:54 PM

Could be dirty contacts in your adjustment wheel.

chrislk02 · #3 08-11-2007, 04:07 PM

I pulled the CCU unit out, all the solders seemed ok and there was no reason for me to believe there were dirty contacts. I believe the problem has something to do with the compressor.

I first noticed a clicking noise today, and it appears to be coming from the compressor. (It looks like the clutch is not engaging). I tried jumping the low pressure switch to see if it would cause the compressor to engage however showed no difference. I tried charging it with some R134, however it caused the fuse to blow all together. Any other ideas?

chrislk02 · #4 08-11-2007, 06:14 PM

I think I am getting closer to the problem. Spent several hours trying different things and trying to narrow down the problem. Here is what I have so far.

1.)In regards to the previous post, the strange clicking noise is unrelated apparently and is not the compressor
2.)The compressor kicks in a few seconds after starting the car (evidenced by watching it and also seeing a slight RPM drop as it kicks in). It however a few seconds later it either -
a.) Blows fuse #1 (seems to only happen with blower on high)
b.) Kicks out and RPM's return to normal. I cannot seem to get it to cut back on again even for a short time unless i shut the car off and restart it.

Any reccomendations?

sdpartz · #5 08-11-2007, 08:00 PM

Check the Klima relay (a/c relay), it's located on the passenger's side fire wall with the fuel pump relay & the ECU. Access through the engine compartment it's covered by a plastic bezel. You can swap with a known working relay just to test it.

chrislk02 · #6 08-11-2007, 10:53 PM

Ok, Ive pulled the klima relay. I am going to try and test it tomorrow. Do you have any advice on the best way to test it? What is the best way to determine if it is the klima relay it self or one of the relays inputs?

chrislk02 · #7 08-12-2007, 01:00 PM

Thanks for the prompt reply. I got a little more troubleshooting information, not sure if it will help. I checked the voltage going into the low pressure cutoff swtich and it was battery. Coming out is next to nothing so i jumpered the switch. The compressor kicked on and ran for probably 30 seconds before fuse #1 blew. I will be hooking the AC pressure gauges up here in a minute but was wondering is that the expected outcome if you run the compressor with low pressure (blowing the fuse)?

saumil · #8 08-12-2007, 01:59 PM

Yes, possible, if it is too low, the compressor will tend to sieze. If the system is virtually empty, would need to evacuate and recharge, make sure you also add some oil when you recharge. The pressure switch is open possible because of low pressure. If the fuse blows even after you have recharged the system, the compressor clutch coil may be shorted. Infact, check the resistance of the compressor clutch coil (with car off), it should be between 2.5 and 3 ohms, anything lower could indicate a coil short.

chrislk02 · #9 08-13-2007, 10:24 AM

Ran out of time to work on it for the weekend. However wanted to post this in case somebody else came looking.

When referring to the mercedes benz repair manual and troubleshooting guide in relation to the KLIMA control box, it refers to them by pin number. I spent some time troubleshooting and putting it together but finally figured out which pin was which.

^ ^ ^ ^ ^
towards front passenger seat

1 5 7 9 11
______________
o - o o o o
o o - - o o
----------------
2 4 10 12

(note, the numbers reference the socket pin holes after the kilma relay has been pulled)
This again was for a 1985 mercedes 190E.

mctwin2kman · #10 08-13-2007, 03:45 PM

I just recharged my 1986 190E and the problem I had before is still there. Unless I am moving and the RPM's are off idle my AC works. As soon as I stop and the engine idles my Compressor shuts off and of course has to be reset via turning ignition off and back on. All is well then. If I rev in Neutral and hold the gas at anything over idle the compressor will still work. Any ideas!

saumil · #11 08-13-2007, 03:55 PM

Either the engine speed sensor, the compressor speed sensor (if this car has one) is faulty or belt is loose/slipping on the compressor pulley. When the Klima relay detects a speed mismatch between engine and compressor rpm, it cuts off the compressor to protect the belt. The difference in speeds should be greater than about 30% to activate the cut-off. In the procedure I listed in this post, there are steps to check the voltage signals from these sensors.

chrislk02 · #12 08-13-2007, 05:26 PM

I will look at the troubleshooting guide I have. I went through the steps to troubleshoot in my troubleshooting efforts. It involves pulling your klima relay, jumping two connectors to force the compressor on (for short term only) and taking a reading between two other contacts. The problem is, i cant remeber which contact is which.

psfred · #13 08-13-2007, 08:34 PM

The usual cause for this behavior is a slipping belt. Check the side with the grooves -- if there are cracks or pieces missing from the ridges, you need a new belt, and likely the problem will go away.

Sadly, you will also likely need a new belt tensioner too, a royal PITA.

Peter

mctwin2kman · #14 08-14-2007, 09:39 AM

Belts not slipping at all. Funny thing is it actually worked fine yesterday. When it shuts off the pressure on the low side is about 34psi. Maybe I just need a hair more R134! I know the low pressure switch point is 2 bar so maybe it is too close. If I held the RPM's up near 900 ish when at stop lights the compressor never kicked off and I was surprised when I got in the garage and idle'ing that it was still engaged. Also no matter what CC unit I use, have tried three, the darn normal AC button does nothing. Only max AC works. Being that you guys have done more than I have I am wondering if there is an easy answer or not. I will go through the tests over the weekend when I have more time but for now was wondering.