I've consulted online charts about "normal" pressures, both hi n low sides, and for the life of me, I can't seem to ever seen a hi side pressure of 300-350 psi at around 100 Fahrenheit! I've also consulted the great oracle of youtube and the priests of automotive air conditioning always show lo pressures of around 30-40 psi. The pressure chart seems outta whack and in my 96 Dodge Ram 1500/5.2, I've never seen lo side 30-40 and hi side 300-350 on a hot day when it's working good. did some system maintenance recently, recharged the system. Cools great, proper charge, BUT the pressures are cattywompus, any ideas?

 

I have the same question. I added some R134a recently as my '96 Ram 2500 5.9 magnum was not properly cooling and has a very slow leak (haven't added R134a in several years now). Since I was in a rush, I simply added some R134a as opposed to vacuuming and recharging the system and the low side was in the low 50s range on a 90+ hot and humid central VA day. Once the AC has run for just a few moments, the duct output temps inside the cab go as low as 45 - 50 degrees. It would be good to see a what the high and low side should read on a given outdoor temperature and relative humidity for a properly charged system.

 

Well dog...'ol blue was roughly the same as your beast. I had a leaky hi pres valve and I thought I'd replace the orifice tube at the same time. My low side press, at approx 100 degrees, mid 40's on the lo side, n the hi side, approx 225. The inside vent temp after about 10 minutes of a/c was roughly 55 at idle and 47/48 at 1500 RPM. Cab gets nice n cool. I also rinsed the evap core with a water hose thru the hole where the evap fan is mounted...but the hi-priests of youtube a/c repair get different #'s, ALWAYS?!?

 

If your a/c compressor cycles properly, and your a/c performance is good, don't worry about the pressures. If it ain't a problem, don't fix it.

High side pressures are VERY dependent on Orifice tube design. The new one that you installed may not be as much of a restriction as stock......

 

I hear ya. I'm more bewildered now than ever because I keep reading how "the original specs don't matter" on many issues I've faced with my mechanical conglomerations of wonder over the last 40 years. Next thing I'll prolly discover is how compression rings and torque specs are meaningless...unless they're not?!?