testing for non-condensables

[thecarpenter]

Can someone explain this "comparison between the liquid refrigerant pressure and corresponding saturation temperature at ambient conditions " can show if non-condensables or foreign gases are present???
I mean excessive high side pressure does not always mean moisture in system, could be over charge, no fan (ok, some things are obvious), but exactly how can I use these tests to pin down moisture?
Thanks
Greg

[heatingman]

add a pressure tap to the inside of the condenser, if there is not one already.

Close the refrigeration service valves. Turn on ONLY THE FAN.

let it run for a few minutes. Test the pressure and compare to the corresponding temperature on the gauge. That temperature should match the outdoor ambient.

I am not aware of this test being accurate when the system is running.

This test can also be useful in finding what refrigerant is in the system on refrigeration units.

[thecarpenter]

Could you explain the science behind this? I guess I never thought the refrigerant was in a liquid state in the condensor coil when the unit was off. So if moisture is present, corresponding temp would be off(higher?), fan is to ...?
Thanks for your help
Greg

[beenthere]

The fan is to coll the refrigerant to ambient temp. Without the fan running, solar heat could raise the temp and pressure of the refrigerant above the ambient temp.

[saylor240]

see below>>>

[saylor240]

Could you explain the science behind this? I guess I never thought the refrigerant was in a liquid state in the condensor coil when the unit was off. So if moisture is present, corresponding temp would be off(higher?), fan is to ...?
Thanks for your help
Greg

The Science behind it is Every freon has a Temp/Pressure Chart and The pressure is Relative to the ambiant air. For example I can put a pressure gauge on a Can of R22 freon and compare that to a PT chart and tell you the ambiant air temp. Now IF i know the AMbiant temp, and Know the pressure of the Gas and have a chart I can

[71CHOPS]

Dalton's Law....the law of partial pressures, states: that the total pressure of a mixture of gasses is equal to the sum of their individual pressures.

[jpsmith1cm]

Dalton's Law....the law of partial pressures, states: that the total pressure of a mixture of gasses is equal to the sum of their individual pressures.

Pure refrigerant will reflect the pressures on the PT chart. Those pressures are saturation pressures. Yes, it means that liquid can be present, but vapor can also be present at those temperatures. It's called saturation.

Add non-condensible gasses to the container (system) and you will see higher pressures.

[Redwood650]

Nice test. Thanks!

[woody19]

Pure refrigerant will reflect the pressures on the PT chart. Those pressures are saturation pressures. Yes, it means that liquid can be present, but vapor can also be present at those temperatures. It's called saturation.

Add non-condensible gasses to the container (system) and you will see higher pressures.

And the only place a P/T chart is accurate is when there is a mixture of liquid and gas i.e. the cond. or evap. coils.

[jpsmith1cm]

And the only place a P/T chart is accurate is when there is a mixture of liquid and gas i.e. the cond. or evap. coils.

Yes.

Where it gets exciting is when dealing with blends and the temperature glide.

[Pete954]

Came across this thread and I don't know what exactly a pressure tap is. Is it a line piercing valve? If so, don't those have a reputation for leaking after a while? Any info would be greatly appreciated. Thanks in advance.

[Dustykyle]

Came across this thread and I don't know what exactly a pressure tap is. Is it a line piercing valve? If so, don't those have a reputation for leaking after a while? Any info would be greatly appreciated. Thanks in advance.

Self piercing valves are for DIY home owners, under bid jobs, or lazy techs. They do not exist in refrigeration systems.