Automotive Air Conditioning Information Forum (Archives)

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

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?

Thanks,
Bob B

Chick on Thu September 30, 2010 9:21 PM

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...

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

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

Thanks, Chick
I'll give that a try.

Bob B