The lower the lowside reading, the colder the evaporator can get, which is fine if you have a freezer since you are not trying to cool warm humid air, but can cause problems on an automotive AC system. If I do top off I would shoot for 36 psi on the lowside. Too much refrigerant will cause the high side to increase which only place extra stress on the system.

Most shop uses a machine that add refrigerant on the high side without the need for the compressor to be running. The refrigerant is added by weight and not by a PSI.

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2006 Infiniti G35
2001 BMW 3.0I E53 X5 Build date 08/2000 SOLD
Lotus Europa 1970 Destroyed by fire
Lotus Europa 1970 S2 Renault Powered
Lotus Type 52 1970 Twincam Webers Powered
PORSCHE 911 Targa 1982 The Garage Queen
Audi Avant donated to Kars for Kids
BMW 525IT Sold
Audi 4000CS Quattro Sold
Jensen Healey Lotus Powered Sold
Opel 1900 Sold
Triumph Spitfire 1971 Sold
Triumph Spitfire 1968 Sold
Plymouth "Cuda" 340 Six pack SOLD