Determining Target Superheat & Target Subcooling

[vava1]

In determining target superheat and/or subcooling is it best to have the HVAC/R (A/C unit) manufacturer's chart or will the generic/universal target superheat charts or hand calc's suffice? I have not yet been able to locate a target subcooling universal chart. Thank you. Jon

 

[MintJulep]

Sort of depends on where you are standing when you take the shot.

 

[Shophound]

Always best to have an OEM charging chart if you can. How the system is charged will depend on what type of metering device it has. If fixed metering it will be via superheat. If a TXV it will be via subcooling.

In any case, to check/commission a unit properly, both superheat and subcooling readings are essential. With fixed metering, superheat will vary widely with load and head pressure. With a TXV, superheat will be much more consistent over a variation in load and head pressure, provided the system is charged properly and airflow is good. Subcooling tends to be more consistent with a TXV as well, as the device has the ability to "stack" refrigerant in the condenser coils (granted we're talking a/c vs. a system with a receiver) if the evaporator heat load is reduced.

If you have no charging chart, there are apps available for smart phones/tablets that can assist in approaching correct superheat or subcooling values. I've used these and find them pretty accurate. Any time you get out a psychrometer and measure wet bulb temps and go from there, you're going to get closer than the guy who goes by "beer can cold" methods.