My a/c quit blowing cold 50 degree vent and now only blows cool 70 degree vent. So I hooked up my gauges and I'm getting 40 on the low and 250 on the high, when I rev it up to 2,000 the low goes to 10-20 and the high goes to 300-330 all the lines are hot except the one from the compressor low side to the expansion valve. Also my expansion valve use to make a hissing noise and now it doesnt. Now heres the part I dont understand when I shut off the a/c the pressures dont equalize the low goes to 90 and the high goes to 250. I think the expansion valve maybe bad or there is a restriction somewhere in the system. Also I converted the system to freeze 12 last year and it worked fine for the whole summer and up untill last week. Any Thoughts?

 

Certainly sounds like the expansion valve is restricted, be the logical place to start. I have no experience with Freeze 12, I always convert to R134a. Was the system properly evacuated when you recharged last time?

 

Does the accumulator a.k.a. receiver/drier have the sight glass on it? If so, do you see any bubbles or liquid bouncing around?

Either way, it sounds like a dissasembly is necessary.

 

Yes the system was properly evacuated and recharged to the proper amount and the sight glass shows the freon moving just like it should. Here is the weird thing it did the same thing last year, the expansion valve quit making noise and the a/c quit blowing cold so I replaced the drier pulled vacuum on the system and recharged and the expansion valve started making the hissing sound and the a/c worked great. So I think I may have to replace the expansin valve flush the evaporetor pull vacuum and recharge. Also does anyone elses expansion valve make a hissing sound my 85 also does it with a full charged R12 system and it works great.

 

mine hisses but only when the A/C first turns on or after I turn it off and the refrigerant equalizes in the system.
Also, mines an 88 converted to 134.

But, you're saying it did it last year when the same thing happened. I'd have to guess you've got some rust or congealed (thickened) oil in there that just happens to hit the orifice just right every now and then. So yeah, you need to flush it out good.