I don't know, but I wonder where you are headed with this. The '96 uses
R-134a, which (as I have learned the hard way) keeps its secrets more than
R-12 did. The high side pressure will tell you very little that is useful.

I always did my own A/C service back in the days of R-12, and could decently
charge a system by sight guage, by hi/low guages, by air vent temperature or
by ear (listening to the compressor cycle rate). None of those things work
on R-134a, as I have learned to my embarrassment. If you have doubts about
the amount of charge, the only way to correct it is to take it to a
professional, have it evacuated and charged by weight. It's too easy to
overcharge the system and "slug" the compressor, damaging it.

On the DIY front, make sure the electric condensor fan is running. If it
quits the pressures won't change much but the cooling will drop
significantly.

Mike

There isnt a HP side valve on the 800 / 70 series.- its read by the ECU via
a transducer by the washer bottle which controls the compressor and
condensor / rad fan accordingly.

Recharging properly is accomplished in one of two ways:

a) completely vac out the system and then recharge with the published weight
of R134a- this is a belt and braces approach, which will work 95%

b) hook upto the ECU and monitor the HP side via the scan tool as you charge
with gas upto around the published weight, and then use the ecu reported HP
figure to get the charge to the 'ideal' level.- this is the prefered method.

Tim..