01 sunfire a/c not running right

My sons 2001 Sunfire has an issue that I need some help on. His air conditioner seems to want to cycle on and off when the car is running with the a/c on. I can hear a clicking noise and the motor seems to draw down when it does this. He has freon because I had that checked. Anyone have any advice on this issue?

thanks for any assistance,

mlh

How did you check the R-134a refrigerant? (Freon was phased out by '96) The only two possibilities for short-cycling are low refrigerant (most likely) or a faulty pressure switch, either high or low side.

We tried to put a can of the R134a in his car, but my friends gauge was at 45 lbs I think? He said that it didnt need any more? that is just what he told me.

Might have to look into the faulty pressure switch. How does one check that or would I need to get it to a mechanic? thanks for the help

mlh

45 PSI on the low side with the engine running? That's about where it should be, toward the high side of "OK", but the compressor should keep running with it there. If that's with the engine off, it's way low. Statically, the system PSI should be close to the ambient temperature in degrees Fahrenheit, but there's liquid in the lines too. You can have almost no liquid refrigerant and still read a "good" pressure from just vapor, but with almost no refrigerant in there. a 2 LB system will show "good" PSI with about .5 LB in there, and it will short cycle and hardly cool at all. The reason for the short cycling is the low side pressure switch goes open (or sensor reads low) and the clutch is disengaged to prevent damage to the compressor. The pressures must be checked with the system operating.

When I check the pressure switches/sensors, I use a scan tool and look at the reading. Some read the actual pressure (sensor) while some read just "open" or "closed" (switch). I'm not sure, but taking a guess I'd say an '01 is probably one that has a switch. If so it will have two wires to it. If it's 2 wire, just check to see if the switches are open or closed. The A/C switch and both pressure switches are in a series circuit, so if any of them are open the clutch kicks out (almost always, it would be possible for the PCM to have a switch connected to it rather than a sensor, but I don't think I've ever seen something designed like that). I forgot to list the high temp switch on the compressor in my last post, check that too. If it's got sensors (3 wire), you can still test them with a voltmeter, but I couldn't tell you which wire to check without looking at a wiring diagram, and I don't think I've ever seen a voltage/pressure graph/table for A/C stuff anyway, but I've never looked for one since I use a scan tool.

No matter what you find, ultimately you will have to take it to a shop to have it fixed, or at least to have the refrigerant sucked out and to have it recharged. If you pull the part out and just let the refrigerant spray out, not only are you breaking a federal law, but you'll also lose an unknown amount of oil. A/C machines measure the oil removed so you can put the same amount of new oil back in. Too much or too little oil is bad. For recharging it, you have to remove all the air from the system or it will never cool like it should, plus the cans are a bad way to do it. Smaller A/C systems need the exact right amount, a high or a low charge will make it not cool as good.