What's the first step in heater/klima diagnosis ? - PeachParts Mercedes-Benz Forum

strelnik · #1 12-23-2016, 01:31 PM

This is a note especially to former/current W126 owners.

The car: a 1982 300SD OM617.951 with about 200K on the clock

Originally, when I picked it up the former owner told me that the Klima didn't work at all. As I drove it to my place, I kept fiddling with the buttons and got the defrost blower to provide generally hot air but in defrost mode only.

My past experience with a 350SDL (to be continued) indicated that this setting was the default on the 126 models.

So what's the next step? My intent is

1. Make all the heating controls work

2. Fix the AC and use it in the summer.

I have been told there's a valve to replace in the cooling/heater system, it's about 40.00. I replaced this on the 350SDL when told by a man who knew less than he claimed that this was the primary issue for the HVAC systems on the W126.

I am ok taking my time learning to fix this, I just want to be on the right track when I start.

Gotta do the timing chain after this too!

sixto · #2 12-23-2016, 02:40 PM

The first step is to clarify nomenclature and symptoms if only for me. The Klima relay came along around '85 or '86 when AC compressors gained an rpm sensor. The Klima relay considers a number of inputs in particular compressor rpm vs engine rpm to determine whether it's safe for the engine to keep driving the compressor. I don't think there's a relay external to the ACC controller in earlier MB Diesels let alone one specifically called a Klima relay. But maybe Klima is the old world term for AC or climate control in general.

Defrost only provides hot air though the compressor should be engaged to dehumidify the air. Good luck feeling anything cold when the heater's going full tilt as in defrost. So at least that works

Things to check (not comprehensive, off the top of my head):

- ACC vacuum system = is there solid source vacuum to the solenoid bank by the front passenger's left knee? Are the appropriate solenoids energized based on ACC mode? Are the vacuum pods holding vacuum (so to speak) and functioning?

- blower motor and control = are the brushes making solid contact? Are the bearings in good shape? Are there burned coils in the resistor pack?

- PBU = are there broken solder joints?

- monovalve = is there a ground signal to the monovalve in cooling modes? Is there continuous +12V to the monovalve when the engine's running? Is the cartridge sealing element intact? I heard MB stocks the cartridge again!

- auxiliary pump = add a fuse!

- compressor = does the system hold pressure? Is the system charged?

Sixto
83 300SD

strelnik · #3 12-28-2016, 03:03 PM

Quote:

Originally Posted by sixto

The first step is to clarify nomenclature and symptoms if only for me. The Klima relay came along around '85 or '86 when AC compressors gained an rpm sensor. The Klima relay considers a number of inputs in particular compressor rpm vs engine rpm to determine whether it's safe for the engine to keep driving the compressor. I don't think there's a relay external to the ACC controller in earlier MB Diesels let alone one specifically called a Klima relay. But maybe Klima is the old world term for AC or climate control in general.

Defrost only provides hot air though the compressor should be engaged to dehumidify the air. Good luck feeling anything cold when the heater's going full tilt as in defrost. So at least that works

Things to check (not comprehensive, off the top of my head):

- ACC vacuum system = is there solid source vacuum to the solenoid bank by the front passenger's left knee? Are the appropriate solenoids energized based on ACC mode? Are the vacuum pods holding vacuum (so to speak) and functioning?

- blower motor and control = are the brushes making solid contact? Are the bearings in good shape? Are there burned coils in the resistor pack?

- PBU = are there broken solder joints?

- monovalve = is there a ground signal to the monovalve in cooling modes? Is there continuous +12V to the monovalve when the engine's running? Is the cartridge sealing element intact? I heard MB stocks the cartridge again!

- auxiliary pump = add a fuse!

- compressor = does the system hold pressure? Is the system charged?

Sixto
83 300SD

Sixto,
Thanks for your help.

To clarify " Klima" is the slang German word for "Klimatisation" or AC.

I will now systematically look at the HVAC/Klima system and report on what I find, once the car returns from the paint shop

BillGrissom · #4 12-30-2016, 04:30 PM

Confused me too. People here usually use the term "Klima" to refer to the 1985+ AC clutch relay box which has "Klima" in white on the side.

If yours has the push-button switches w/ the red-white-blue temperature setpoint wheel, that is the same as 82-85 300D & 300SD U.S. cars. There are 2 other boxes involved, a TemperatureRegular and a Blower Speed Control, both above the glove-box liner. All of them have problems w/ cracked solder traces and old capacitors that need changing. But, even when new and working as-designed, the system was a bit confusing. Read the owner's manual to understand how it should work. There can be long delays between when you command a warmer temperature and you notice anything happening. One example is that a temperature sensor in the coolant keeps the fan from running until the coolant has warmed up. The original upper-class buyers wouldn't tolerate cold air blowing on them.