92 q45 AC HELP

[bigox777]

I'm not getting any power from the hot wire coming from the wiring harness that plugs into the AC compressor. I checked the AC fuse and the relay. What else could be wrong? I also jumped a hot wire directly to the compressor and it cut right on, so I do know that the compressor works. I 've gotten great help on this board before and all help will be greatly appreciated. Thanks

[DAEDALUS]

I don't have a manual with me now, but I know that there are at least 2 pressure switches on the system. I'm pretty sure at least one of them controls the relay. The ones I'm thinking of are on and near the receiver/drier. Disconnect the connectors (not the switches!) and take continuity readings at the junction.I have a similar problem, except with the condenser fan. It won't turn on, but it works if jumped. I'm replacing my drier and switches this weekend, assuming the parts are here by then.

[Q451990]

The pressure switch will typically cut out if pressure is too low - as well as if it's too high. This means a very low freon charge can prevent the system from coming on at all! I'd check the pressure readings on the low and high sides before replacing anything else. I'm in the middle of A/C repairs on my 97 Nissan Truck as we speak... talk about fun!

Heath

[bigox777]

I swiched over to 134 last year. Yesterday when I checked the line off of the wiring harness for power , it was not hot at all. If the pressure is to low, would it cut the power off? If so why?

[DAEDALUS]

I just checked the manual...page HA-64 in my copy shows the wiring diagram. There's only one pressure switch on the compressor-side of the system. The other pressure switch and a temp switch control the condenser fan operation. The switch on the compressor circuit is a dual-pressure switch, just like Heath said, which means that the line pressure has to be within a range for the compressor to turn on. Too high or too low and it will not. At normal operating temps, R-134a is slightly higher in pressure than R-12. Might want to ask a parts guy, but I don't think the difference alone in a properly filled system would be enough to shut off a good switch. Shutting off the system if it's low on pressure is to protect your compressor from working against too little fluid and getting damaged.

[DAEDALUS]

When you did the switch, hopefully they flushed the system out real good to remove the old oil. R-12 and R-134a oils of the past were not compatible, and both sucked up moisture when exposed to air and formed acids. I also hope they replaced all the o-rings and the drier.

[bigox777]

Thanks for the help. I'm going to work on it in this weekend. After the systems evacuated , do I have to jump the compressor to charge the system?

[DAEDALUS]

Check the switch before you evacuate the system to verify that's the problem. If it is, then either replace the switch or recharge the system and then recheck the switch. Once you get a good switch in there, and the right amount of R-134a, you should be fine. Running the compressor sometimes helps to pull a charge...I can't comment on a can-fill or how long that would take. Best to rely on their instructions. Usually you can get enough in there just from expansion to close the switch without having to jump the compressor.