airconditioning

I'd look on the name plate of the system, or would know because it's my job.

Maybe you could ask the manufacturer of the equipment about the working fluid?

Nitrogen is used for pressure testing. Refrigerants such as Freon family, Hydrofluro carbon family (HFC134a), natural refrigerants like Ammonia are used in the refrigeration system. The refrigeration system has to be tight so as not to allow the refrigerant to leak out or the surrounding air to enter into the system. SO generally pressure test is conducted to ensure leak tight of the system. (150 to 400 PSIG). Nitrogen or CO2 can be used. Nitrogen is preferred as it has less moisture content. Also it is required to flush the system to remove the dusts in the refrigerant pipe line by blowing with nitrogen or CO2. Refrigerant leak can be detected either by soap solution or by using electronic leak detector.

It is most unwise to carry out a pressure test with a compressible fluid, lest the test should fail producing a catastrophic mechanical self-disassembly. Use an incompressible fluid instead. Water is the simplest one to use.

Under a hydraulic test, a leak will show as a fine jet of liquid and a rapid decrease on the test pressure gauge when the system has been isolated for its test period.

Tests using compressible fluids should be carried out to a lower pressure than the water test pressure, and always afterwards.

your trying to determine if the existing pressure is caused by nitrogen or a refrigerant I assume?. contact your supplier or simply use an electronic leak detector, to determine. most systems do not come precharged with more than 3-5 lbs of nitrogen pressure.