Hi: Searching for half hour and can't find what the recommended low side pressure should be for 02 x-type auto climate control touch screen idling in driveway with ambient temp of 87 fahrenheit. Gauge suggests 25-45 is normal; my car is making 27. I was having the warm side cold side problem and found my temp door blend motor (one at bottom of the triangle) was getting weird signals from its brain so I jammed the door in full cold for arizona desert operations. Eventually that will have to be fixed right but am wondering if the system is fully charged or not? Coldness is subjectively better but still not like my old 72 olds with frigidaire r12. I won't put any r134a in if 27 is normal. Thank you. --Tom in tucson

 

The pressure should be about 28 to 35 PSI while at 2000 RPM with inside fan on high and off of recirculate(outside air coming in)..If you add any R-134a, make sure to purge the hose of any air first..then let a little in at a time until the return line (suction Line, or larger one where you're putting in the refrigerant) just becomes cold and sweaty (At 2000 RPM)...Your vents outlet temps should be around 45 to 55 degrees with proper air flow...Also check your Pollen filter..if it's dirty, it will cause a low suction pressure.

 

Refrigerant 134a is not like R12 as far as pressures go.
The pressures can look correct when the system is a little low.

You can get an idea of the charge level but just a low side reading can be misleading.

The best way to know if the system has the correct charge is to weigh it.
A/C machines recover the refrigerant and have a scale to weight it.

The high side should be considered if you are just relying on gauges.

bob gauff

 

I disagree with you..the Pressure/Temps are very similar..that's why this HFC R134a was created to mimic the CFC R-12 characteristics and operates at very similar pressures and temps as CFC R-12 did..in evaporator temp range of 40 degrees...High side temps/pressures are going to be all over the place because ambient temps and air flow over the condenser vary so much.



I will agree that to properly charge a system ..one should recover what is left in the system and only recovery machines can act as a recovery machine and not as a true vacuum pump for complete evacuation..but if the system is free of air and other non-condensables, the the recovery machine can remove the system's charge down to 10" of vac..then a weighed in charge should be done...But I've been working on MVAC systems to all the way up to 500 ton R-123 industrial Chillers and can charge by feel and some pressure/ temp readings to get real close to proper charge...as I first explained in my original post here...