W126 - M103 - A/C Pressure Switch Query
 

From what I read at Fast Lane, the pressure switch on my receiver-dryer serves as both a 2 bar low and 30 bar high pressure switch.

The red switch is fan related; not refrigerant. Could anyone confirm if this single switch does indeed serve as a low/high pressure switch?

Photo below in acpart.bmp file.

Thanks for your time.

I'm not sure which is which without looking, but yup, one is for the fan, and the other is hi/lo pressure.

That is the pressure switch. If you have a CFC12 system with original parts, it's probably a low-pressure switch only.

The high-pressure switch is mandated for HFC134a systems, which is why it's there in the replacement switches. Note that this switch is not a cycling switch - it's not supposed to shut down the compressor during normal operation.

So my original MB R-12 system only has a LOW pressure switch? That might make sense as all of my other R-12 cars only had a LOW pressure switch, but the description of the switch in the photo at the Fast Lane section here says 2bar low - 30 bar high.

If you look at the wiring diagrams, you'll find that it is a hi/lo pressure switch originally. I don't know how far back they were used, but I see the switch in diagrams for 1988-91 300SE.

http://img340.imageshack.us/img340/8...eswitch0xy.jpg

They weren't used in '83, that I do know, but there's no downside to having one in there. The replacement will always have the high-pressure switch.

Note that many cars have a low-pressure switch on the low side, to cycle the compressor. Yours is not among them, as the low-pressure switch is on the high side, and will only prevent the compressor from starting in the first place.

$$Pit/Matt:

I appreciate all of the information.