What is 'superheat'.

[TJ Hopland]

I see references to it in Pontiac and Cadillac manuals in the AC compressor service sections.  What was it?

["Cadillac Kid" Greg Surfas 15364]

TJ,
The simplist explanation of super heat as it refers to the Air Conditioning cycle is "that amount of heat added to a liquid/vapor mix after all the liquid has turned to vapor".
What this is in fact is the heat added as measured by the increase in temperature over the "boiling point" of the refrigerant vapor at the evaporating pressure.
The TX valve, bulb, measures the temperature of the suction line and compares it to the evaporation pressure and controls the refrigerant flow to maintain a constant "superheat".
The superheat switch in the compressor compares the pressure and the temperature and by those two values, decides if the refrigerant charge is excessively low (or at least the refrigerant flow to the compressor).  If it (the superheat switch) senses excessive superheat at that point it grounds the contact and "blows" the fuse shutting power to the clutch to protect the compressor.
I hope that answers your question.  If not let me know.
Greg

[R Schroeder]

A little more info .
Roy



http://contractingbusiness.com/residential/cb_imp_17963/

[TJ Hopland]

Interesting.  I though it was perhaps a feature to make the ac colder.  I guess in a way it sort of its, it makes it colder and keeps working.    I bet that is something most people messing with AC systems dont have a clue about. 

["Cadillac Kid" Greg Surfas 15364]

 TJ,

Without getting into the thermodynamics and dynamics of the Refrigeration compression cycle, "superheat" energy is essentially nearly "worthless" for it's cooling effect in the evaporator, and it is added energy that the compressor and condenser must work against.
It's "measurement" by TX valves is simply the method that they employ to ensure that all the refrigerant is evaporated (in the evaporator), and that no liquid refrigerant is returned to the compressor suction, where it would cause damage to the valves, pistons and anything else that moves in there.
Greg