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AC Compressor Pressure Readings & their Meaning

A/C Infographics    

Many of us come to a conclusion that if the vehicle's AC fails to blow crisp, cool air, the cause is a malfunctioning AC Compressor. This may not turn out to be true all the time, as the AC could have failed due to a fault in some other component. Therefore, instead of leaping to a wrong conclusion, it is better to ascertain if your AC compressor is really at fault. You can check your pressure readings against the infographic above/chart below to narrow down the problem and remedy for your AC Compressor.

 

AC Compressor Pressure Problem with the Compressor Remedy
 

High 250 Low 50

 

Overcharged system or condenser issue Recharge system and inspect condenser for blockage
 

High 160 Low 10

 

Evaporator frosted or low pressure piping faulty, or expansion valve Check and replace as required
 

High 225 Low 80

 

Expansion valve too wide open, heat sensitizing tube faulty, or too much refrigerant Recharge system
 

High 50 Low 50

 

Clutch engages then disengages Check wiring, run power straight to the compressor to test
 

High 150 Low 30

 

Water in the system Evacuate for 30 mins, dry and refill
 

High 125 Low 30

 

Not recharged enough or too much oil Check amount of refrigerant/oil
 

High 150 Low 30

 

Ideal reading Ideal reading
 

High 200 Low 70

 

Blockage in system Find blockage and replace
 

High 150 Low>10

 

Expansive valve open or leak Check valve or complete dye test
 

High 100 Low 100

 

Compressor does not engage Check wiring

Note: The most ideal pressure readings are around 150 high and 30 low.

Warning: Remember, venting 134a refrigerant into our atmosphere is illegal and bad for our environment.

The following table presents the possible inferences and the actions that can be taken, based on the level of pressure registered by the high and low pressure gauges:

Low Pressure Gauge High Pressure Gauge Inference/Action Required
In range In range AC is working properly
Low Low Add refrigerant
Low High Need service, possibly blockage of the expansion valve or orifice tube
High Low Need service, possibly faulty compressor
High High System is overcharged. Slowly remove refrigerant. Venting is illegal in USA

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