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Am I undercharged?

70monte on Fri October 10, 2008 6:20 AM User is offline

Year: 1992
Make: Chevrolet
Model: Cavalier
Engine Size: 2.2L
Refrigerant Type: R12
Ambient Temp: 72
Pressure Low: 29
Pressure High: 165
Country of Origin: United States

I just competed the repair and recharging of my 92 Cavalier's AC system. I stayed with R12. The system calls for 36oz of refrigerant and I used three 12oz cans. My final low pressure was 29 and high side was 165 with an ambiant temp of 72 degrees. My vent temps at idle were 37 degrees. My book says low side pressures should be 37-47 and high side 150-325. My low side is lower than this range but vent temps are good. Does the lower pressure mean I'm undercharged or is my low side pressure fine?

The only reason I question this is because each time I removed a can from the can tap, there was a little release of pressure and what looked like a little bit of refrigerant. I wasn't sure if I was getting all of the refrigerant out of the cans. This leads me to my second question.

How do you determine that you have gotten all of the charge out of the cans? Is it when you can no longer feel any liquid sloshing around? Is it when the can no longer gets cold?. I'm just not sure if I'm getting the full amount of refrigerant out of the cans and thus wondering if I still don't have 36oz in my system. Thanks.


Chick on Fri October 10, 2008 8:02 AM User is offlineView users profile

using small cans is rough when you try to guess at the charge, but yes, you lost some in each can. I would "guess" that you are about two to three ounces less.. Don't go by the pressures listed as they give you a wide variance, and your pressures look fine for that ambient, but a couple more ounces would be better, and now you need to be careful not to overcharge it...

Email: Chick


Freedoms just another word for nothing left to lose

70monte on Fri October 10, 2008 12:58 PM User is offline

Thanks for the response. I do have a digital scale which I tried to use when I initially was charging the system but with the hose hooked up to the can and tap, the weight would jump around because the can wanted to tip over. I will have to try and find a way to have the can sit on the scale without wanting to fall over and just open the low side enough so that only about two ounces go into the system. The vent temps are plenty cold now but it seemed like the vent temps were a little colder before the repair.


mk378 on Fri October 10, 2008 1:49 PM User is offline

37 from the vents is really good. You can't get much lower without freezing the evaporator, and the system will start cycling the compressor to prevent that. You should wait for warmer weather before trying to fine-tune. Also it is hard to store a partly full can of R-12. Once it has been tapped, the tapper usually leaks slowly.

70monte on Fri October 10, 2008 4:42 PM User is offline

Thanks for the advice. I think I will do what you suggest and wait until it warms up. Its supposed to be about 81 degrees on Monday. Even then, I might just wait until next summer. As far as the partially full can of R12, its probably going to go to waste regardless because unless I get all of the correct parts to redo the system on my 1970 Monte Carlo, its the only other vehicle that I have that would require the R12. My other 92 Cavalier I converted to R134a two years ago and its AC still works fine. Thanks again.


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