I bought some gauges (and AC book) and refrigerant for my truck and added refrigerant according to the manufacturer's specs (from Haynes manual).
The compressor will turn on and cycle at 45+ psi, but doesn't stay on. It's rated and charged at 60psi (low side), which is normal.
The high side pressure is low, at around 120 psi when it should be much higher in the 400 range.
The pressures do equalize when the engine is off. When the compressor comes on, the low side measures 0 psi and high side 120 psi.
Ambient temp is 95 degrees F here.
There is no cold air.
Do I need a new compressor or could it be something else?
Not sure what book you looking at, but high side pressure should be two times ambient temp. Expecting 400psi means it is approx 200 degrees where you live. If the low side is truly zero, then you need to research how to properly fill an empty system. If that haynes manually actually says it needs to be 400psi on the high side, throw that book away and get a better manual. You do not fill based on pressures. If it were me, I would put more in via the low side.
And btw, if you have low pressures on a properly filled system, it means there is a restriction on the low side somewhere.
Ah yes, I am sorry that was a typo there. I should correct that. If the high side should in fact be twice that of ambient temperature in degrees F, than ~190 psi should be the closer to the correct pressure? The low side pressure reads 60 psi when the compressor is cycling, but when it's shut off.
I have read quite a lot in the Haynes AC manual, and I have a hypothesis that air is not properly flowing on the evaporator core. Maybe because the air valve is not working. I'm going to take a look at it to see if the evap core is even getting cold soon.
I think there could be moisture in the system causing the restriction when the refrigerant line gets cold and it freezes up and I need to get it emptied and cleaned too, but I don't have another system to test or compare anything on.
The low side should be in the 20-30 psi range, and the high side on a hot day will be in the 150 - 200 psi range (NOTE: do not charge to these numbers, there are several variables that go into this, but this is just an order of magnitude, or a reality check). If you run the system up to 400 psi, you will be replacing the entire system.
What year truck do you have? I am assuming that it uses refrigerant R-134a.
I mistakenly said 400 psi. According to my AC manifold gauge papers, for my conditions (95 degrees F I should roughly have 50-55 psi low side / 275-300 high side. It's a year 2000, and it takes R-134a.
but I realize now this is probably incorrect and I'm looking for a better explanation and specifications on this AC system.
Also the AC clutch will not engage unless there is at least 45 psi there. I have replaced with switch twice with the same results.
Thank you both for helping out.
Anyone with a similar year/truck with AC working know the normal high and low side pressures?