Automotive Air Conditioning Information Forum

I have a manifold gauge set that I used to charge an empty system by weight to factory spec with a refrigerant scale. The manifold gauge set still has some refrigerant/gas in it as I just closed the valves off and hung it up when I was done.

So, do I need to vent/empty the manifold gauge set before checking pressures on this or a different car?

Does the manifold gauge set need to be reading all zeroes anytime I go to check pressure on something going forward?

Unless you use different manifolds for different refrigerants, yes clear out the gauges and zero them out for accuracy. You should not mix oils either. It is best to have a different set for different refrigerants.