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1989 Isuzu Trooper - Low/High side A/C Pressure

Bob B on Thu September 30, 2010 6:35 PM User is offline

Year: 1989
Make: Isuzu
Model: Trooper
Engine Size: 2.8L
Refrigerant Type: R134a conver.

Just recently converted from R12 to R134a. The orignal compressor blew Flushed system,
replaced compressor with PAG150 oil as recommended for R134a and drier.
A/C is cold on intial start up but when system gets hot it takes a constant higher rpm 1800+ to
get it to put out as cold as initial startup. Charge with 85% of charge designated for R12 of 2.1#.
When outside temp is 105`F, the high side pressure starts to creep over 300 psig. The low side varies about
40-50 psig. Can anyone offer suggestions for improvement? What should the approximate Low and High side
pressure be at a given temperature?

Bob B

Chick on Thu September 30, 2010 9:21 PM User is offlineView users profile

When it comes to retrofitting, there is no set pressures, rather keep your pressures in line and have proper cooling.. You could be slightly overcharged.. At those high ambients, I would recover the charge and start with about 65% of the R12 charge and "slowly add an ounce at a time until the inlet and outlet of the evaporator are the same temp..Giving a few minutes for the system to stabilize..The suction line should be slightly colder going back to the compressor.. It's not that small a system, so just take your time and you'll find the right charge with the best cooling...

Email: Chick


Freedoms just another word for nothing left to lose

Bob B on Fri October 01, 2010 10:23 AM User is offline

Thanks, Chick
I'll give that a try.

Bob B

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