rule of thumb 2 to 2.5 X ambiant temp for high side or 175 to 200 lbs
30 to 40 lbs low side

With R134a it's common to see high side pressure between 2.2 and 2.5 times ambient temperature. On that same 80 degree day we would see between 176 and 200 PSI on the high side of an R134a system. The system operates in a specific range based on outside ambient temperature. High side pressure has a broad range relative to temperature because of heat load on the evaporator, humudity, airflow across the condenser, and engine speed.

 

A heater core block off valve will help keep it a good bit cooler........



This is one of the cheapest and most enjoyed mods that I have done!

 

I added an automatic vacuum-operated valve in the same place Bill's, above, is mounted.

If I had to do it again, I think I would put in a manual one like he did.

It really does decrease the duct outlet temperature for the A/C system, as it keeps hot coolant from still circulating through the heater/A/C box under the driver's-side dash when in air-conditioning mode.

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