I'm no A/C guru so hopefully some more experienced members will chime in. What your low side pressure is indicating, is the pressure of the refrigerant by the evaporator. If you know the pressure of refrigerant, you know its corresponding temperature simply by looking at the pressure/temperature chart for that refrigerant. That is what the pressure is telling you, not the amount of refrigerant in a system.

Ideally, you'd like a low side pressure of about 27psi with R-134 at the evaporator. That means your evaporator temp will be slightly above freezing. The hotter it is outside, however, the harder it is for heat transfer to take place so your low side pressures will generally be higher as outside air temperatures increase.

Remember, a 30 pound container of refrigerant will show the same pressure at any given temperature whether it has 30 lbs of refrigerant in it or just 1 pound. The same is basically true for your car.

A/C work can be complicated and dangerous. Its best to leave it to a professional unless you really take the time to learn.

Good luck.

Scott

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Scott
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