Trying to get the a/c running in my 94 945. The compressor does not switch on. I assumed it had insufficient pressure and needed a recharge. With a can of r134 from Kragen however the gauge read excessive pressure (motor not running): 100psi with ambient temp 90f. At what pressure does the high pressure cut off switch activate in this system, and would it keep the compressor from running at all?

100psi at 90 degrees without the system running (Static Pressure) is not too far from normal. The high pressure sensor will only turn a running compressor off at about above 300 psi system pressure.

Were you able to get the system to take the can you hooked up? Was it one of those cans with the built in guage?

It could be a bad low pressure switch not letting the compressor turn on. It is mounted on the accumulator. You can unplug the connector and jumper the terminals in the connector to see if the compressor comes on and the system cools. You might just need a new low pressure switch if this works.
Good info on the 700/900 FAQs pull down menu above... explore! I have a 92 240 & your system may be a little different so maybe another 900 guy can help even more.

Hope this helps!
Danny Mac

Thanks for the suggestions Danny. I now think that it may be an electrical problem with the control unit, after reading the FAQ. I had initially looked for voltage in the connector to the compressor clutch when it was hooked up and the car was running w a/c switched on, and I got no voltage. But when I jumpered it the clutch worked. So I checked voltage when the plug was disconnected and it was getting 12v--which is exactly what someone on the FAQ describes as a symptom of cracked solder joints on the control unit--voltage but insufficient current. I think the pressure switch is ok.

If it is the controller, I have some experience with that. Some have had good luck with reflowing the old solder, but I found that this fails again unless done completely, by removing all the old solder and putting new. Or, replace the small relay, which I have also done. Both seem to work.

Well it was indeed the solder joint on the controller--exactly as pictured on the faq.

I resoldered it yesterday and the a/c is blowing cold now. Once I got the compressor running I took another pressure reading with the gauge on the refill can and it would drop way down when the compressor engaged, causing it to cycle. Adding a can of the refrigerant seemed to do the trick. I will just have to wait to see if the solder fails again. At least i will know exactly what needs to be fixed! In the mean time I will enjoy this chilly air. Thanks everyone for your suggestions.

Glad to hear you got it fixed! The 945 is a really nice Volvo. I used to have a 745.. very roomy & I could haul 4x8 sheets of plywood in it.. sort of a white collar pickup truck!

Danny Mac

Which relay did you use?
--
john

Good luck.. I hope you get it going!

Danny Mac