Sorry I didn't finish explaining .
I was only referring to what a bad mix AIR is with A/C systems .
An example is AIR/Compressed air being used for a leak check (PREASURISING A SYSTEM) OR flushing a line if that air meets and mixes with the compressor oil . Boom can occur. Always nitrogen, clean safe, inert . added benefit it helps absorb MOISTURE in the system. If a system has been open for a prolonged time or LOW on refrigerant it can run in a Vacuum where AIR can enter , If air enters so does moisture. Only 2 good ways to remove moisture .1 use nitrogen and allow it to stay long enough in the system to absorb, then purge it off. DO NOT run the system with nitrogen inside. 2 A good vacuum . IT Can only be measured with a vac u stat. A good Vacuum is 1000 microns and lower. the ideal vacuum is 500 microns and lower. This unfortunately can not be measured by gauges.
Also remember with car A/C systems that were not designed for 134A from manufacture The condenser just cant do the job properly . Meaning the condenser needs to be a lot larger or the refrigerant charge lower. A poor compromise . TX valves should always be changed if a system changes refrigerant . More flow is required with a LESS yielding refrigerant . High head pressures are MOISTURE in the system, secondly Restrictions. Or a inefficient condenser, Remember also oil migrates around the system with the refrigerant. DO NOT blow it to places in the system where it cant return unaided. Thank you for the link. a good read I am new to forums and still finding my way. No disrespect meant for anyone.