Refrigerant reclaim

Hi Guys

Today i was reclaiming gas out of a domestic unit it works fine. but no need for it any more and also another condensing unit which boss said was working fine.
In both the cases after when i reclaimed the gas and before i disconnect hoses or purging wait to see on the manifolds of any pressure rise, all of a sudden heard a bang noise out of compressor of the fridge and the condensing unit.
and then the pressure rise on the gauges.
I was wondering what that noise was perhaps the refrigerant trapped under the oil but not sure.

Thanks Guys

I've never heard the bang noise, but yes, refrigerant will get trapped in the oil and then explode out violently. Sometimes it doesn't happen until you try to move the unit.

It's really annoying when you start to pull the unit out of position and it blows oil out the suction service valve, over you and the customer's shrubbery. BTDT.

That would explain why the textbooks say you should rap on the compressor with a hammer or mallet when reclaiming prior to disposal of the unit. Interesting.

While pulling gas from the low side of a cold compressor on a capillary system, there are two types of noises. One is the refrigerant "boiling" out of the compressor oil and the second.... and somewhat noticeable, is the piston moving suddenly due to the difference between pressures acting on the underside of the piston and it's position in the bore verses the discharge valve reed leakage that is trying to stop higher pressure refrigerant entering the bore.

when recovering cap tube systems I hit both lines, and ALL WAYS whack the comressor good with a hammer less ye be bathed in oil!

at about 20inches I give it a good hit, then at -25 I hit it hard enough to make a dent then let it get down as deep as it will go and stay there!