W126 - M103 - A/C Pressure Switch Query - PeachParts Mercedes-Benz Forum

Mike Murrell · #1 03-02-2006, 05:13 PM

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.

Moneypit SEL · #2 03-02-2006, 05:17 PM

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

Matt L · #3 03-02-2006, 05:40 PM

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.

Mike Murrell · #4 03-02-2006, 05:50 PM

Quote:

Originally Posted by Matt L

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.

Moneypit SEL · #5 03-02-2006, 07:12 PM

Quote:

Originally Posted by Mike Murrell

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.

Matt L · #6 03-02-2006, 08:25 PM

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.

Mike Murrell · #7 03-03-2006, 09:04 AM

$$Pit/Matt:

I appreciate all of the information.