Air compressor pulley was not engaging on 94 Nissan Quest. Started to add some R134a and after a few seconds the center of pulley engaged but will cut out after a couple of seconds. Continued to charge but pulley keeps engaging and cutting out. Pressure was between 50 and 55 psi when engaged which was what the table on the can said it should be for 90 degree ambient temperature. Should I continue to add more to see if it stays on?

1. Check the compressor has engaged. Identify the location of your compressor. Look at the pullyer and you should be able to see if it spining or not. The engine running turn the A/C on max cool, set fans high, and make sure that the clutch is engaging on the compressor. The pulley spins any time the engine is running. The center part of the A/C pulley only engages when the A/C is on. If the clutch is engaging and disengaging rapidly, the refrigerant may be low. For more info check here: http://www.mercedesmedic.com/ac/

It sounds like you've done just about everything except to check if there is a bad or intermittent wire causing this or perhaps your low-pressure safety cutout switch is possible going bad causing the compressor to kick on and off?

The squeeling is the belt because the air compresor is likely seizing. At idle it can't turn the compressor, in motionthe compressor probably turns and cools the air. Most air conditioners come on when the defroster is on.

If the compressor is not engaging (the center is not spinning) then it's likely that the r134a is low in the system

Add a an or two to make it work better.

Also, make sure the radiator fan goes on when you turn the a/c on.

Good luck to you.

Locate wires coming from compressor clutch and trace to nearest plug that you can unplug. Turn on A/C to max cooling. If clutch not engaged (center of compressor drive pulley not spinning with pulley), unplug compressor clutch wires and use multimeter to check voltage going to compressor clutch. If voltage is around 12 volts or more, then clutch should be engaged when plugged in. Plug clutch wires back in (with motor still running and ac set to max). If clutch still not engaged, then clutch definitely bad because 12V signal should engage it.

I would check the following possibilities:
1. Is compressor clutch working? - You need to do this when the ac is blowing hot air only - locate compressor drive pulley on engine - rubber belt wraps around it. Start engine and set to max ac. When the ac is blowing hot air, look at the center of the compressor drive pulley using a good flash light - watch it for a while, it should be spinning with the pulley - this means the compressor is engaged. If not, the compressor is not engaged. If your ac is blowing hot air, then the compressor should be engaged and running (trying to cool). If it is not engaged, then your compressor clutch is probably going out. Could be low voltage to clutch, but more likely the clutch is worn out and only working some of the time. Note: if working normally, the compressor clutch will engage and disengage in cycles- but the air should always be cold. If clutch is bad, compressor would need to be replaced (sold as one unit). This is tricky to diagnose and could take some time - you need to do it when ac is blowing hot air but set to max cooling.

2. Low on refrigerant or refrigerant has moisture in it? If your ac blows cold initially after being off for a while, then heats up, and continues to regularly cycle back and forth between hot and cool air, then the system may be low on refrigerant or the refrigerant may have moisture in it that is freezing and restricting refrigerant flow. An a/c shop can check refrigerant level and even replace refrigerant if moisture is suspected.

Could be other issues, but I would start with these.

Good luck

used to be a big deal. today, you can buy kit from autozone or other auto store and do it yourself. Need to discharge R12 into reclaimer so it does not go into air and pollute air.

Then, install R134a fittings on lines, add r134a feon in proper amount with new oil. leave old oil in system. you can buy cans with oil already in the can with the freon. probably need about 6 ounces of oil.
lot's of websites tell how to do this. vidoes on line too.

good luck

You should see it right by the compressor pulley. It will be a aluminum colored tubing with a cap on the port. The compressor pulley is the one that engages and disengages when the a/c is on.

To reset your AC compressor, you need to remove power for at least 15 minutes. After you reconnect, the compressor should turn on. If it does, immediately turn to high and try to add refrigerant. Best of luck.
Greg

I hope you are adding R134a & not R-12. I think you are just confusing them.
our problem is a leak in your a/c system somewhere. Your a/c should cycle about 4 times/minute. When you add refrigerant, you are refilling the system and making it work again. The system only holds about 3 cans of refrigerant. If you are doing yourself, get a fill hose with a gauge on it so you can see if it's "ok" low or high pressure.
The leak will probably require pro ehlp.