My 91 240 sits a lot. Not a daily driver. I'll drive it and have ice cold a/c then 2 days later no a/c. The compressor does not come on. Then a week later cold a/c again. Etc.etc. There is power at the switch on dash and the switch works but no power at green wire that connects to compressor. If I jump power to compressor it works and A/C is cold. Suggestions experts? Where do I start trouble shooting?

 

You have to go backwards in the system until you find a voltage loss. I would first check the pressure switch on the accumulator. It cuts the compressor on and off to keep the pressures in balance.

 

indeed, from the dashboard control panel, the first stop is that sensor on the side of the drier-reciever aka accumulator. if you unplug that sensor, and jumper the wires together and your AC works, then the system pressure is too low, or that sensor has failed.

 

thanks. I will try work on it this weekend. Is there a way to test sensor? And can u replace sensor without evacuating system? Somone told be cuz this car sat for 5 years that the orifice tube may have trash in it and causing the pressure to change? What should the pressure read if I hooked a gauge to it? Do I hook it to the low or high side? Thanks Pierce, sorry for all the questions.

 

pretty sure you need to evacuate the system to replace that sensor. ad no, I don't know what the pressures should be, I leave all a/c work to the pros with the proper equipment.

 

You would check the pressure on the low pressure hose or on the dryer can. The 1st issue would be if you have any pressure at all. If 0 then that would most likely be why your compressor doesn't turn on. If 0 then look for the leak and repair it. Then flush the system and replace the orifice valve and recharge it. As for the sensor it is either on or off so no pressure it is an open contact and with pressure it is closed. If you remove it and there is gas in the system it will escape. Oh as a warning the freon will freeze your eyes and fingers so wear protection when working with it.

 

Not so. The pressure switch in these cars can be removed without loss of refrigerant, no need to evacuate the system.

 

awesome. Is there a way to test the switch?

 

Yes , no pressure then no continuity

 

in other words, if the switch is working AND you have freon pressure, then the sensor should be closed, if you unplug the harness connector from it, you would read zero ohms across the two pins of the sensor...

after checking the sensor resistance, probe the pins of the harness plug, one of them should be +12V relative to ground when the A/C control is switched on, if its not, I'd be looking at the dashboard control panel next.

if you do see +12V on the harness plug, jumper the two pins of the harness plug together with the engine running, and the compressor should engage.

 

The above advice is correct. If you connect a jumper wire across the wiring harness to the switch, the compressor should come on. That would confirm that the circuit works.

Don't be tempted to simply jumper out the switch as a solution. The compressor must cycle on and off otherwise you will have an ice ball in the dash.

 

Ok. Had the day off and tackled this issue. When inspecting the pressure sensor harness I noticed it had old electrical tape wrapped around it. I removed it and found this mess. The green wire is split in two inside the butt connector. I rewired it with heat shrink connectors and everything is now beautiful. A/C now works everytime its turned on. Thanks to all the great advice. You guys are the best.