All you a/c techs

[blacksnapon]

You hook up gauges to a vehicle that has a no ac complaint. The pressures are somewhat normal (maybe a tad low), the compressor is engaged, there is no outward signs of trouble, and the blend doors are working correctly. Technician a says the system is overcharged. Technician b says the system could be charged with air only. Who is right? A only---B only---Both A and B---neither

 

[Brian_B]

Subscribing. I know even less about AC than anything else.

 

[Fellro]

Hmmm, interesting question...would someone really be dumb enough to charge a cooling system with air only? maybe I shouldn't ask that... An expert I'm not, but if the pressure read right, but a shade low, it should atleast cool. How about blockage in the evaporator? (no airflow across it)

 

[blackhat620]

Neither a or b.

If there is no complaint, i am assuming the unit is cooling, and since the compressor is engaged and both gauges are reading normal or slightly low then the system is either charged correctly & the outside ambient air temp is low or the system is slightly undercharged.

If the system contained air then the gauges would show high head pressures and the system would have high operating temps.
If the system was overcharged then you would also see high head pressures. High head pressures will also result from a dirty condener or reduced air flow over the condenser.

If the high-side pressure is high you will also have high low-side pressures, and if the high-side pressure is low you will have low low-side pressures as the system must achieve a balance point.
Now if you have a High low-side pressure only (the high-side pressure remains low) then the compressor is defective.

Undercharged = both high-side & low-side pressures are low.
Overcharged = high-side pressure is high. The low-side pressure will be high if the evaporator temperature is high.