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The term would be psig not psi. Proper psig for any a/c unit auto or not is a 40 degree evaporator and you would convert 40 to psig runningng a pressure temperature chart with engine running at 1500 rpm. I its usin R-134A the psig that equals 40 degrees Fahrenheit is 34.9 psig =40 degrees Fahrenheit at 1500 rpm. In fact , 34.9 psig is the pressure for 40 degrees no matter how many rpm. Use 40 and be safe. Don't forget ,40 psig at idle will be much lower as rpm rises and evaporator could freeze up depending on humidity and ambient temp of truck inside.

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13y ago

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