AC high pressure problem on 240

[ItsOnlyTV]

My 1993 240 wagon AC's compressor does not kick on unless I bypass the high pressure switch. Then the AC works great. Nice and cold. it is an R134a system.

When running, the freon pressure is about 35psi - pretty good.
If I quickly hook up high pressure switch, AC keeps working.

When not running, the pressure is 75psi. And of course, the HP switch doesn't let in come back on and I'm back to square one - need to bypass switch again.

My questions...
- Does it sound like a high pressure switch problem?
- Is 75psi for AC normal for car at rest?
- What are the concequences of permenently bypassing the HP switch?

Thanks

[jimmy57]

You are talking about the switch on the high side line buried down below radiator or the switch on the low side line in back of engine compartment?
In either case it seems you need to inspect the terminals and if those are OK then replace the switch. You do need to be sure you ID the correct part.
Static pressure is system is temp dependent and R134a is about 1 psi/degree F up to 90F and then it gains a little to maybe 1.2 psi/degree F.
If it was 75F when you checked this then that is expected pressure. This assumes your gauges are accurately zeroed.
Those switches can fail. The diaphragm can leak and the outer part is sealed well and initially it offsets the switch open pressure before it leaks externally or the top pops off the switch and dumps the refrigerant. On that car the switches are installed on schrader valve sealed ports.

[ItsOnlyTV]

Thanks for your help.

I am talking about the switch on the receiver/drier in the back of the compartment (#5). According to a diagram in Bentley's 240 service manual, that is the high switch. But whatever it is, that's what I'm referring to. As far as the gauge, it's simply one that came with a can of freon. Not sure of accuracy.

So if it is on a schrader valve, it should be a simple swap with a new one?

from 240 Service Manual by Bentley Publishers