The gauges are an important tool and reading the low and high side pressure can give you clues as to faults within the system.
Ill add more to this as time goes on so come back regular
The out side of the gauges read in PSI you can use this to see if system is functioning ok , you will need to take a static pressure reading that is with the system off and compressor not working and both low and high side pressures equalised. There is formula here that says if gas is R134a then the outside temperature on the day if degrees F should be close to the static pressure in PSI.
Next take a reading of the system pressures with the A/C on and the compressor engaged, the low side should drop from the static pressure and the high side should increase. A good reading would be 35 low and 180 high but this can differ with temp and humidity on the day.
These gauges also have a temp gauge on the inside for popular auto refrigerants and these temps can be used to advanced fault find the condenser and evaporator.
But for this level of fault finding we can just use the PSI readings.
Low pressure in low and high side
Possible problems could include, Low refrigerant gas due to leaks or just through loss over time in auto A/C systems - top up refrigerant to test further . A restricted receiver drier could cause this check and replace. Expansion valve plugged or defective could also cause this problem
Normal low side pressure but high side is high pressure
Could be restricted condenser, check and replace any faulty components.
lower pressures low side and normal pressures on the high side
Could be caused by defective thermostatic switch
High pressure low side and low pressure high side
Could be caused by faulty or worn compressor , incorrect fitting of hoses
High pressure on both low and high sides
System overcharged check static pressures , Condenser or even Radiator plugged externally preventing good air flow , condenser fan motor or actuation switch not working
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