There should be a schrader valve on the fitting. There is always the possibility it is bad or someone previously removed it.



Cut from my Ford manual:

Clutch Cycling Pressure Switch


Removal and Installation

1. Disconnect wire connector from pressure switch.

2. Unscrew pressure switch from suction accumulator.

For installation, follow removal steps in reverse order. Use new O-ring lubricated with clean refrigerant oil and hand-tighten switch only. Check system for proper operation.

 

Replaced the sensor that screws into the accumulator with a new one. The accumulator itself is only 1 year old (replaced when I did the r134a upgrade). Checked the pressure with a set of gauges - 40 psi on low side, 45 on high side. Ran truck and A/C. Gauges still read 40 and 45 psi. Still no voltage at the compressor (note: replace compressor fuse with a new one recently).

 

I'd swap that accumulator pressure switch again just to be sure, but sometimes, those things have a large range from when they open until they close again. You are definitely low on refreigerant. Static pressure with the high and low side equalized and the system full should be 100-120 psi depending on the temp outside.

Go ahead a shoot some more R134a in and get the low side over 50 psi and see if that gets the cycle switch moving and back to life. it might just be stubborn after sitting for so long.

And yes, there should be a schrader valve under it, so it might shoot a small shot of gas out, but it should stop as you unscrew it more.

 

Unplug the low pressure switch and use a paper clip to jumper the plug on the wire harness. Turn the AC on. If there is STILL no voltage at the compressor, you have a wiring issue somewhere else, and the low pressure switch is not the problem.

If you DO have voltage at the compressor with the harness jumpered, then the low pressure switch is the problem, or you're low on refrigerant.

 

I tried putting a jumper across the sockets in the plug that plugs into the sensor on the accumulator and the compressor started running. The issue is with the schrader valve mounted on the accumulator that the sensor screws on to. The sensor is brand new and the accumulator is only 1 year old, but one of them is not working properly and I have to discover which it is to get the A/C working again. Thanks for all the answers that were provided to this thread.

 

What did the gauges read when the compressor kicked on?

 

You are low on charge as previously indicated. It's not a switch issue, it's doing what it is supposed to do. There is a designed in "dead-band" where the contacts are open until ~45 PSI. The contacts close, the compressor kicks on, when the low side drops to ~25 PSI the contacts open again.

In a properly charged system the low side will start to equalize with the high side, implies low side will rise to ~45 PSI when the contacts of the clutch cycling switch close again. The cycle repeats. In very hot weather it is not unusual for the compressor to stay energized for a very long time.

This is another reason why you need a manifold gauge set to see the low and high side at the same time. It would have saved you a lot of aggravation and guessing.