Hello all,

I'm working on an 83 500SEL and I can't seem to locate all the controls for the A/C system.

When the car came in the blower motor didn't work along with the A/C so I replaced the controler in the dash. Blower working now.

The system is charged, that I know. I tried jumping the low pressure switch but no effect. I checked and have no power going through the switch so I found the relay in the fuse box and switched it with another one and still nothing. I checked the ground to the compressor and thats fine, and all the fuses.

I was wondering if there are some kind of switches under the dash that the wiring would pass through on the way to the comp?
I can hot wire the comp and it works fine so I have a charge, and the comp works.

With the switch on the dash set to A/C I have power on 30 and 86 on the relay but no ground on 85. If I ground 85 I get the relay to click but I can't find what controls 85?

Thanks in advance!

Ron

Which system? AAC or port/dealer installed?


Joe

__________________
Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.
Raleigh NC
919-881-0364

Good question Joe,

As far as I know its a gray market car, came over on the "boat" and the only thing that was done to it was make it conform to US standards.

The A/C system seems to be factory from working on it, the wirings is to perfect to be an after thought.

Hope this will be of help

thanks

Ron

Bump...

C'mon, someone must have some ideas!!

I'm begging here

Toxicant,

I'm a little confused by your post.

At the top you say that you jump the pressure switch and nothing happens, then later you say that you hot wire the compressor and it works fine.

By hotwiring, do you mean you jump voltage directly from the battery? If you jump voltage directly around ALL circuitry and the compressor comes on that only says that there is something somewhere in the circuit that is not putting voltage to the clutch.

Secondly, you keep saying that you KNOW the system is charged, but I'm still not clear why you think that. Have you put gauges on the system?

Good luck,

Hi Larry,

I know the system works because I have put power to the clutch with the car running and everything works fine other then the fact I can't control the comp with the controls on the dash.

All the doors seem to work and fan control but there is no signal going out to the pressure switches or comp. I've checked the relay and that is fine so somewhere between the control in the dash and the comp clutch there has to be some device thats failed other then the two pressure switches. Or a bad ground I suppose.

Thank you,

HI Ron

Looking at a wiring diagram for a USA version 126 pin 85 of the relay goes straight to ground. No control if it at all. The push buttons provide power to terminal 86, via the pressure switch on the drier, which turns the relay on passsing power from 30 to 87. The ground for this relay is location G102 which is behind the instrument cluster. I also see it shares a ground with a ACC control unit. Which part did you replace? I'm a little confussed on what part it is since there is 2 controllers and the push buttons for this system. If it is a bad ground then grounding pin 85 would make the system work. A simple test would be ground pin 85 then put the system in to EC mode and see if the compressor shuts off and on in any other mode.

This is the same for all years 1981 to 1985 126s' with Automatic Climate Control. Sounds like you have a OEM system so this should be valid for your car even though it is a Euro version but not promising you that. It could be differnet but for the most part this kind of stuff is universal for Mercedes.


fasthair

HI Ron Again

Do over. Re-reading your last post I see you say you have no signal to the pressure switch. How did you check this and what did type of signal did you look for? You should have battery (B+) voltage (12volts) at the low pressure switch. If not then either the push buttons (PB) are bad or the Evaporator Temperature Regulator (ETR) is open or fuse 10 is blown since that is where the PB get there power. The ETR should be located in the heater box just to the right of the gas pedal. Check for B+ on the Black/Red wire of the ETR if none PB is bad. If power is going to it but none on the other wire ETR is open and needs replaced.

fasthair

Just a little footnote, i had the same problem with my 85 500 sec, the blower worked but the a/c did not. I ernt through all kinds of things, wiring, compressor, etc., to find out that it was the ignition switch, which is actually a common problem with the 126. I dont know what the wiring setup is for the switch, but for some reason the a/c compressor is connected to it in some way, probably through some relay. With a little jiggle of the key back and forth the compressor would kick on and off. Dont know if this helps, but there are many threads in here about the 126 ignition switches.

I still ask how you KNOW that the system is charged. Have you put on gauges? If the pressure is low, the clutch will still come on when you jump power to the clutch.

If the system charge is low a low pressure switch will be actuated that will interrupt the compressor circuit. I haven't seen anything in your posts that indicate that you have checked for that.

Good luck,

Larry,

I interpret his statement to be that refrigeration is not the problem. This means to me that it gets cold when jumped. If it gets cold the low pressure switch will be tripped.

I haven't decided what A/C is involved here though. Most grey 126 cars don't have the pushbutton controller. They all probably involve an ETR switch though.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Lets see if I can answer some of your questions.

The a/c system in this car is factory installed, there is no doubt in my mind. The car is loaded with leather, abs, airbag, hydro susp, heated seats...the list goes on. Besides, I've looked at all the wireing and there is no way it could be an after thought.

I have no power to my low pressure switch, the cooling fan doesn't run in a/c mode and no power to the comp clutch.

I took the system charge down and converted it to 134a. The machine I have will put the proper charge into the system. I did this after I started to work on the car so hence, there was no a/c before I switched to 134a.

If I supply a power and ground to the comp clutch with the engine running the a/c works fine, as in it will cool down to about 42 degrees.

There is no ground to the relay so I was wondering if the system supplied the ground to the relay, I've been a little hesitant to start supplying grounds and powers to un-known circuts so I don't fry anything.

So what I was looking for was perhaps another "switch" or "sensor" that the ground might have run through before going to the relay. Fasthair might have the answer for me but if you could tell me where the "ETR" is that might save me some time.

Thanks all for the help, keep it coming

Ron

Ok, this morning I supplied a ground to 85 and have power going to 87, both 87 and 30 are hot but still no power to my low pressure switch.

I checked the ETR and have power going in and out so its not that. What I replaced was the push button controler, I had no blower motor and that took care of that problem.

You mention two other controlers for the a/c system I was wondering where they were located and is there a way for me to check them?

Thanks

Ok, latest update!

I have power to my low pressure switch now, had some wireing problems near the switch. So power in and power out.

I also found a bad resistor under the master cylinder and replaced that and now I have the aux cooling fan running when in a/c mode but still no power to the comp. clutch.

I think I'm getting closer just one more silly thing and I'll have this licked....

Thanks all '

Ron

There should be a relay behind the motor to the center of the master cly. Check it, control for the clutch. Klima relay.



Joe

__________________
Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.
Raleigh NC
919-881-0364

There is no Klima relay on this car. That started in 1986.

Both the manual and automatic air have a relay after the low pressure switch. On the uS aut system the relay is code 3 in the fuse box.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician