AC problem, no power to AC compressor

All vehicles have a low pressure switch to protect the compressor when pressure gets low.

They also have a radiator fan sensor when pressure gets high. And should have a hi pressure switch to protect the compressor from overcharged. Those 2 might be one sensor though.

You've also got a relay, fuse, power switch and body control module. And all the wiring.

What's your static pressure? It shouldn't be more then 120 psi in the hot south. Less in the cooler north.

Freon contracts and expands with temperatures. Cars won't even operate the compressor in winter time. Anything below 43ish degrees and there's not enough pressure.

My car reads 5 psi in January. 115 psi in july.

 

I called dealer and this one doesn’t it’s a trinary switch they called it, has the low and high in one bunch! So I’ll change it out and see, cuz I got fed up from looking everywhere and that’s the only switch that has wires going to it.

 

I've heard of that but never seen one.

How much is the part?

 

$92.00 CDN

 

I just replaced the trinary switch and compressor still not kicking in! So what now? Would it be the expansion valve? Anyway to test it out?

 

Fuse
Relay
Power switch
Body control module.
Ground
Wiring.

Provided your freon isn't too much or too little

 

That’s one thing with the Freon I ran out like at 3.00lb all could put in !

Checked fuse, relay, the power switch, body control module not sure what that is? Is that like one of the main computers?

 

That's one of the main computers.

On cars it's part of the ac circuit.

Not sure on semis

 

Still have this darn issue. All the correct fresh Freon is in the system with new trinary switch!

 

The few times I’ve had that problem, it was always a bad wire. Couple times the power wire itself was broken/chafed not far from the compressor. On my Freightliner it comes from the starter. I once hooked it up wrong when changing the starter. A couple times the temp probe at the evaporator came unplugged. Other times the wire from pressure switch was broken. Most recently ( 2 mos ago) the plug itself going to the pressure switch was bad. Since you can’t jump the pressure switch to engage the compressor. I’d suspect a bad wire or plug from the switch, or a bad wire or connection on the constant power wire, if you have one. They all come together at the compressor. You could also check for power at the evaporator probe. That would at least establish power to there. With a/c on. If probes good, should light up both terminals sending power to/through the trianary. I’m not good at electrical. I think that’s how the system works. I’ve always been able to figure it out with just a test light.