Low pressure switch resistance

[Kevin]

Of course this would happen 3 days before DCS.

My A/C stopped working today. After much investigation, I think I've narrowed it down to the low pressure switch. My pressures are fine, resting they are at about 90 PSI which is about what I would expect in this weather. So I check continuity across the switch, if my pressures are 90 PSI, the switch should be closed, right? Well I measured resistance across the switch and it varied between 600-3000 ohms. I checked voltage at the compressor, I was only getting about 2 volts. I'm guessing that's not enough to A) engage the clutch and B) tell Dave M's fan relay to turn the fans on. So to test, I put a jumper wire in the low pressure switch connector, and all worked fine. A/C engaged and fans turned on.

The pins on the switch seemed a bit dirty and maybe a little green, so I sanded them down a bit and got them looking nice but it didn't seem to help. Since the jumper wire worked, I guess the pins inside the connector are mostly fine.

So my question is, should there be any resistance at the low pressure switch? It's just a switch, no need for resistance, right?

Do these switches go bad? Could it be an adjustment problem? To replace a switch, I guess I have to open the A/C system, right?

The weather has been warmer than usual lately, if that has anything to do with it.

[hmcelraft]

The low pressure cycling switch just screws off the accumulator and you replace it. Not expensive. Some people try to screw around with them and adjust them - not a good idea. They are not repairable.

The fitting has a valve in it like a tire valve stem. No leakage to worry about if it is working and I have never heard of one failing. There is an o-ring to seal the switch and keep the crap out. The new switch should come with a new one. Use a little refrigeration oil as lube. The oil is inexpensive too.

[Bitsyncmaster]

The switch would have to normally have very low resistance when switched on (above 50 PSI) to power the compressor clutch. Has to be much less than 1 ohm.

[Kevin]

Thanks, all! I guess I'll be seeing if Julee can overnight me a new switch. Good to hear it's fairly easy to replace, too.

[DMCMW Dave]

Thanks, all! I guess I'll be seeing if Julee can overnight me a new switch. Good to hear it's fairly easy to replace, too.

This is one of those parts you can replace with NO tools. Just unscrew it and screw the new one on. There is a danger that the Schrader valve under it is leaky so be prepared to work fast.

[Grover]

I spent a whole lot of time figuring out why my A/C stopped blowing cold. Nothing would fix the issue, pressures were fine, new condenser, new hoses, etc. Finally decided to replace the low pressure switch as it was one of the only things I didn't replace since owning the car. As soon as I did that, everything was normal.

As others have said, don't mess with it and just replace it.