R-12 subcooling in automotive

[mastmec]

I have been trying to find some sort of subcooling chart for r12 or superheat for TXV or orfice system. Any help would be appreciated. Thanks.

 

[MintJulep]

There is no such thing as a sub-cooling or superheat chart.

Refrigerant charts are for saturated conditions. Sub-cooling or superheat are measures of how far away from saturation you are.

 

[rmw]

I take care of a bus with a large A/C system on it, and while it has no "chart" it does have a specified range for superheat at the exit of the evaporator in order to prevent returning liquid to the compressor. Without looking it up, I think I remember it is 8°F when set at specific cold air conditions.

rmw

 

[rmw]

I did have an occasion to look this up, and I found that my memory was not complete. The SH value recommended for my system ranges from 6°F to 14°F of SH measured at the evaporator outlet. (Which is where I got the 8°F, which is the range.)

Now, one other caveat. This is for a R-500 system. R-500 is an azeotrope largely made up of R-12, and acts much like R-12, except without the tendency to freeze up the evaporator at lower pressures.

And, this is used on a system where there are load control (unloader) valves on the compressor whereby successive pairs of cylinders are unloaded as the suction pressure goes down (due to cold ambients) until the low pressure cut out finally takes the compressor out althgether if the pressure continues to drop to as low as 15 PSIG.

I hope this gives you a point of reference for what you are looking for.

rmw