The AC in my 2000 Impreza, was turning off & on, so I bought freeon and added it to the low side of compressor until the gauge read "good." 3 weeks later the AC started clicking off & on and the compressor locked up, so I turned it off immediately. After it cooled down, I turned it back on and it worked again. I hooked up the freeon gauge on the low pressure side and it read in the red, (too high). The compressor locks up. Any idea of what's going on? Why high pressure on the low side?

When you say it was turning off and on, do you mean the compressor was just cycling on and off? Or do you mean it would blow warm then cold then warm then cold?

The compressor was cycling off & on. Even when the compressor is not running, the pressure on the low side is high. Early this morning I turned on the compressor and it ran, blowing cold air. I turned it off because I didn't want it to lock up again.

Simple answer, its overcharged.

The little gauge dohickies they put on the cans are hardly accurate. Need a real set of manifold gauges to watch system pressures while its running to determine if its actually overcharged or if the cheapo gauge is lieing to you.

Except maybe under high ambient temps when idling, the compressor is supposed to cycle on and off. If it was blowing cold air maybe it was fine.

Usually when it's recyling, it's low on freeon. Even if it was supposed to recyle, it's not supposed to lock up. I don't have another set of gauges, but as far as accuracy you're probably right. However, when I 1st added freeon, it was reading low; after I added it the reading was good, but on the lower side of good. It ran fine for 3 weeks, then it started recycling and it locked up & stopped. Then the reading was in the red zone for high pressure' on the low side. Something must have gone wrong for it to run good for 3 weeks, and then start acting up and reading differently.

Maybe you need to use a gauge set then. Harbor Freight has a set on sale cheap sometimes, I think there's one style of it that is better quality. I was reading some info on overcharging refrigeration stuff in general and it said when it's overcharged, it can allow liquid refrigerant to enter the compressor suction line, then the liquid enters the compressor crankcase, and since liquid isn't compressible then it makes the compressor lock up.

Hey, thanks. That makes sense. I'll check Harbour Freight for the gauges; O'Reilly's wants $54. Fairtax4me is probably right on the gauges, so I checked the prices. I forgot to check Harbour Freight, though.

 

Sounds good, right, with the gauge set you tap the high and low side at the same time then after running it for like 10 minutes you can read the pressures. It comes with some charts and other stuff to tell if it's in the right part of the performance curve. I picked up a set but didn't use it because it didn't come with one of the quick connect fittings for one of the taps for some reason. Some auto parts places might let you borrow the gauge set. 

 

I remember seeing reviews for the HF set, there were two styles. One style was garbage and leaked a lot I remember reading that, and some other style got pretty decent reviews. GrossGary had a HF review thread on there some time back; not sure if this gauge set got reviewed ...

 

If it short cycles like the compressor just comes on for a second or so then shuts off and you get a bit of hot/cold cycling at the vents that usually means low refrigerant. But if it's cycling on and off every few seconds and you get nice cold air at the vents it was probably just fine before the excess refrigerant got added.