AC Performance

[Robert Squires]

*Yep, I already have. Read the forty-some posts in the thread "AC upgrades/improvements" Interesting and useful.
*There's a formula of sorts given for determining the quantity of R134A to put in a retrofitted system that was originally R12. It's an indirect procedure of reading hi-side pressure while filling 134A and stopping the fill when the hi-side pressure reaches the formula-prescribed level. The formula given was ~2.2-2.4 (ambient degF) with ~25-30psi on the low side.
*So, on an 80degF day, the system would be full of 134A when the hi-side pressure was 176-192psi. I've been using a chart which gives a range of 175-210psi at that ambient temp. Essentially the same. But there are additional conditions for that pressure reading. Here's my question. At what rpm is that hi-side pressure reading taken. It makes a lot of difference since pressure varies with rpm, even more so than with R12. The reading also assumes that there's a stand-alone cooling fan running in front of the car.
*There are some cool (temp) retrofits out there and then there are a lot more that never should've been done. I agree with one sentiment of the thread, that of leaving R12 wherever possible. But for those that have already been changed, I think that a lot of performance problems can be avoided by just installing the correct amount of 134A.