I have a 1994 Toyota pickup (Hi-Lux out of the US) that has had inoperative A/C since I bought the truck 15 years ago. I've finally decided to find what's broke and fix it as I convert it to something other than R12.

While R-134a is a common conversion, I found some information on alternatives. Among the alternatives, R-152a (a.k.a. "Dust Off") raised its head as an alternative. So I threw caution to the wind and said "what the heck" and tried it this weekend.

I had some trouble finding specific information about this conversion. I'm real interested in finding out what pressures I should expect to see in my system. Here's my experience, but note that this is from a highly suspect system:

1. High pressure seems to be a steady 100 psi. Running or not. This seems a bit low compared to R-134a systems I've dealt with in the past.

(this is where it gets strange):

2. While charging (from a vacuum), low pressure side would not get above 15 psi.

3. As soon as I shut off the R-152 supply, the low pressure side would drop to 15 in. Hg Vacuum. The pump would not shut off (so I suspect a bad pressure switch controling the compressor clutch).

4. When I turn off the engine, the LP side would rise to 65 psi. This seems way high.

5. Absolutely no cooling at the vent. 90F day, 95F+ vent temp with A/C on high and recirculating.

Any information on R-152 and the expected pressures would be helpful. Any help in diagnosing my colling system based on the above would also be appreciated.

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