School me on a/c cutoff switches vs low pressure only switch

[Bailey28]

Got a 84 GM G body with a/c. Converted to r134a but never got the system pressues exactly where I want them.

Sanden SD5H14 compressor, everything is new. New lines, condenser, evap, drier, clutch cycling switch.

I cannot get the system to stop the compressor at 21psi, then switch on a 42 psi. I believe the switches are adjustable and I attempted to adjust the first one with a screwdriver until it didn't work anymore. The second switch out of the box shuts the compressor off at 11psi and switches on at 45...

What am I missing?

 

[mk378]

You're probably using the wrong switch. The one for variable compressors cuts of at 10, because the compressor itself stops pumping around 25. The switch is only there to prevent running after a leak-out with zero pressure. You don't want that one with a fixed-displacement compressor.

The cut-out pressure is more important since the principle of the CCOT system is the compressor cuts out before the low side is low enough to cause the evaporator to ice over (refrigerant boiling point below 32 F). Cut-in pressure is relatively unimportant.

The general rule with auto A/C is once the air is cold you quit messing with it.

 

[Chris142]

If you are messing with an aftermarket switch those are no longer adjustable.

 

[Bailey28]

If you are messing with an aftermarket switch those are no longer adjustable.

Chris you are saying that even though these aftermarket switches have a screw in them they are not adjustable by some amount?
I have this exact switch on the car now.

 

[Bailey28]

You're probably using the wrong switch. The one for variable compressors cuts of at 10, because the compressor itself stops pumping around 25. The switch is only there to prevent running after a leak-out with zero pressure. You don't want that one with a fixed-displacement compressor.

The cut-out pressure is more important since the principle of the CCOT system is the compressor cuts out before the low side is low enough to cause the evaporator to ice over (refrigerant boiling point below 32 F). Cut-in pressure is relatively unimportant.

The general rule with auto A/C is once the air is cold you quit messing with it.

Should I be using something other than the Four Seasons 36674?

 

[Chris142]

Chris you are saying that even though these aftermarket switches have a screw in them they are not adjustable by some amount?
I have this exact switch on the car now.
View attachment 284353View attachment 284354

Yes. They can only be adjusted a small amount. Not enough to help really

 

[14Accent]

Seems like you got a bad switch. The specs clearly say "PSI low off 21".

Maybe try a NOS GM switch? Looks like the part number is 3041336. Ebay shows a bunch for sale around $50:

NOS GM A/C Pressure Switch