[Vetteman61]

1971 Pontiac Grand Safari.

Does anyone know of the max high side pressure on the AC system, or where I could find this information?

[mzbk2l]

I would think just an R-12 pressure chart should get you pretty close? I attached one I found on the web.

[Scott Stoneburg]

What refrigerant are you using? R-12? R134a?

[Vetteman61]

Thanks for the replies. I've converted to 134A. I may be incorrect, but I don't believe an R12 pressure chart helps in this situation because it gives the PSI of R12 at a given ambient outside temperature when exposed to atmosphere, but the AC is a closed system, and more specifically the high side is under higher pressure. I'm unsure of what are normal operating ranges on the high side of the AC. I'm installing dual electric pusher fans in front of the condenser and I'll be using a high pressure line fan controller switch installed in the high side line to activate the fans, but I'm unsure of what PSI to have the switch turn on the fans.

[hgerhardt]

Set the switch to turn on fans at 225 psi or so. Not too critical.

[mgarblik]

I agree with the 225PSI or so in most climate areas. High side pressures in a traffic jam on a humid 100 degree day can creep just over 300 PSI even with fans running. Don't like to see them go higher than that.