Eratic Climate Control

[RavzSa]

Hi All,

Within the last week, I noticed that the climate control unit sometimes shuts off when pressing any of the 3 buttons (RECIRC, AC, humidify) or sometimes just on its own. When I say shut down, the AC switches off, the buttons don't illuminate and the side vents start blowing hot air. I know that when the vents start blowing hot air, that the DUO-Valve has also lost power and the valves are now open...

The CCU comes back on after a few minutes or if you leave the car off for a bit.

Not sure where to start looking, KLIMA, CCU?

Thanks

[Christo C]

Looks like a loose wire somewhere.

[CraigB]

Yes I was thinking bad or burnt contacts in switches - same sort of thing. I think you will have to get in there and start moving things and see if you can trace what part is making a difference.

I always think its unfortunate they didn't make the default position on the duo valve to close off the heat.... we can put a jumper on in winter.... but then the car wasn't designed for Australia!

[RavzSa]

Yeah I was hoping it wasnt that, those cables are like a maze!

I agree, wish those duo-valves were set to close rather than open - I suspect this is historic issue as the PO had blocked off the duo-valve by blocking the pipes to it.

Oddly enough the blower fan is unaffected

[brycedunn]

I've not troubleshooted this on a W124, but if you have the full automatic climate control I've done quite a bit on the W126 which is similar.

The Klima is easy to troubleshoot. It controls the A/C compressor and you can bridge it and see if the compressor kicks on or not. On the w126 it is pins 5 and 7 from memory. If you have the manual there is a whole series of steps you can follow. Probably slightly different on the W124. There is a picture of this section of the W126 manual here:

https://www.classicjalopy.com/2020/03/w ... r-cooling/

I also found that my erratic climate control was due to a bad pushbutton unit. I got a rebuilt one from Programa Inc.
the picture here will show if its the pushbutton unit like a W126:

https://www.classicjalopy.com/2017/10/f ... wer-motor/

Hopefully this is somewhat useful. I've had to completely rebuild the climate control on two W126 cars and at least the earlier W124's with climate control look quite similar.

[RavzSa]

I've not troubleshooted this on a W124, but if you have the full automatic climate control I've done quite a bit on the W126 which is similar.

The Klima is easy to troubleshoot. It controls the A/C compressor and you can bridge it and see if the compressor kicks on or not. On the w126 it is pins 5 and 7 from memory. If you have the manual there is a whole series of steps you can follow. Probably slightly different on the W124. There is a picture of this section of the W126 manual here:

https://www.classicjalopy.com/2020/03/w ... r-cooling/

I also found that my erratic climate control was due to a bad pushbutton unit. I got a rebuilt one from Programa Inc.
the picture here will show if its the pushbutton unit like a W126:

https://www.classicjalopy.com/2017/10/f ... wer-motor/

Hopefully this is somewhat useful. I've had to completely rebuild the climate control on two W126 cars and at least the earlier W124's with climate control look quite similar.

Thanks for this useful info - I eventually tracked it down to a faulty fuse which seemed fine to the naked eye - go figure! I should have started there I guess...

[StraightSix]

Hi,

I realise this is an old thread, but this is the closest I have found to my current issue.

The three central buttons in my W124s HVAC only seem to operate when the coolant has reached full operating temperature.

The main fuse on the block seems fine. Are you referring to another fuse for the HVAC?

Thanks,

Andrew

[RavzSa]

Sorry havent been on here for a while...

Did you come right? The fuse I was referring to was the main fuse in fuse box for Klima.