I'm trying to refill my 1995 Volvo 940 A/C system and I cannot get the cap off the low-pressure service port. See attached picture below. I've tried pulling it off, rotating it off and nothing works; from YouTube videos it seems they should just come off? Any help would be much appreciated.

 

Yes, they just unscrew, lefty loosy, righty tighty - (has right hand threads). If you can't get it off without destroying something and causing a leak - you can take the low pressure switch off, purchase a r/12- r134 screw on adapter adapter (if it fits and depresses the valve in the accumulator) and use that port to fill from the low side. You will have to use a paperclip or something to complete the circuit on the low pressure switch - or the compressor won't turn on.

 

Honk, I appreciate all your responses so far. You've helped me a great deal with this car, and I've been able to do quite a lot of work myself. However, this one is bothering me. I took a basic wrench and it's not coming off. It seems like I probably shouldn't try to grip it with something like a vise grip where I might puncture the system. I looked online and some people were saying there isn't a high pressure port. Anyways, I can't identify another port. Where might it be? And one more thing, after further inspection I did notice this wire separated. Could that possibly be of any relevance to the system itself?

 

Have you tried a 6 point socket?

 

That was it. Went and bought some 134a and the system is already pressurized. I looked at the clutch on the compressor and it's not working. I checked all fuses. Would my next step be to check relay? If so, which one is it? And what additional steps can I look for here. Would that one wire highlighted above be a possible reason?

 

Unplug the connector on the receiver/dryer . It is the low pressure sensor. Take a wire or paperclip and short out the connector with the key on and AC switched on. The compressor clutch should engage (click). If not then it is bad.

 

Also unless they use a different AC compressor there should be a low and high pressure fitting on the back of the compressor.

 

Thank you for the response Jagtoes. I didn't see the high on the back. I looked but maybe I missed it. Just so I know what I'm shorting out, you're talking about the connector circled blue right?

 

There is no relay (well there is - it's part of the control module - and they do commonly have cracked solder joints on the circuit board preventing power going to the compressor - but we can deal with that after you check for power other places)

Looking at the wiring diagram - power for the compressor comes out of the control unit on terminal 10, then to the low pressure cut off switch on the accumulator (7/53) , then to the high pressure cut off switch on the condensor (7/41). If the pressure is not too high or too low - power is sent to the compressor. (8/3)

Note the wire colors to those three components - mostly green with red stripe (or green with black) You should be able to test power flow with your $5 test light - keep in mind the control unit waits about 5 seconds after the car is started (and the alternator is charging) before it will turn on power the the compressor circuit.
If you don't find power at the low pressure switch (and it looks like those wires have been damaged) as I mentioned it's common for certain connections on the control unit circuit board to become cracked - and 90% of the time re-soldering the offending solder joints restores power to the compressor circuit.

Your snipped green/red wire at the accumulator - does that rigged wire go to some aftermarket switch to send power through the compressor circuit (because of a problem with the control unit that someone could not figure out?)