These are the norms:
A/C System Pressure Readings
Ambient Temperature Low Side Pressure High Side Pressure Center Vent Temperature
60 °F 28-38 psi 130-190 psi 44-46 °F
70 °F 30-40 psi 190-220 psi 44-48 °F
80 °F 30-40 psi 190-220 psi 43-48 °F
90 °F 35-40 psi 190-225 psi 44-50 °F
100 °F 40-50 psi 200-250 psi 52-60 °F
110 °F 50-60 psi 250-300 psi 68-74 °F
120 °F 55-65 psi 320-350 psi 70-75 °F
Low Compressor Discharge Pressure
If the pressure on the low side is high the following may be the problem.
1. Leak in system Repair leak in system
2. Defective expansion valve Replace valve
3. Suction valve closed Open valve
4. Freon shortage Add freon
5. Plugged receiver drier Replace drier
6. Compressor suction valve leaking Replace valve
7. Bad reed valves in compressor Replace reed valves
Usually The following applies:
Low Pressure Low
High Pressure Low Low refrigerant Charge
Low side normal
High Side Low High Side Restriction
Low side normal/high
High Side Normal/High System Overcharged
Low side high
High Side high Moisture in the system
Low side Low
High Side Normal Faulty Cycling Switch
System will not operate Stuck open Cycling Switch
ow side high
High Side high Inoperative cooling fan, blocked Condenser
Rent or buy a Vacuum pump hook it to a compressor and evacuate the ssytem.
Evacuating the System:
Evacuation is performed with a Vacuum Pump which literally sucks the air and moisture out of the system. To properly evacuate a system, the pump must be capable of producing 29"hg of vacuum. At 29"hg any moisture in the system begins to vaporize sufficiently to be drawn from the system. The industry norm is to leave the vacuum at29"hg for 30-45 minutes.
Once the connections have been made, turn on the evacuation equipment, open both high and low side service valves on the gauge set.After approx 5 minutes, the gauge readings should be steady at 29"hg. Continue evacuating for another 45 minutes. After this period, shut off the valves in your gauge set, turn off the vacuum pump. Note:It is now that I recommend checking for leaks. Your gauges should hold this vacuum point for at LEAST 20 minutes. If there is any reduction in vacuum readings there is a good possibility you have a leak.Again, with coolant as expensive as it is, you can't afford not to check for leaks.
Just replaced a condensor on my neighbors daughters car and had to evacuate the system afterwards. Both the suction(low) and pressure(high) sides were high. Suction pressure should not exceed 70 psi.
Evacuate and see if it hold pressure for at least 20 -25 minutes. If there is a leak, pressure will go away.
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