UV radiation from sun breaks the CFC molecules at stratosphere  releasing chlorine ion. This chlorine ion is responsible for depleting the ozone layer at stratosphere

Chlorine and Bromine are considered as the elements responsible for the depletion of ozone layer at stratosphere. CFC compound are highly stable at lower atmosphere and have higher lifetime. Therefore they reach stratosphere and depletes the ozone layer. Presence of Hydrogen element in organic refrigerants such as HCFCs and HFCs results in decomposition at lower atmosphere. Therefore these elements have lower lifetime and cannot pose threat to ozone depletion.

Ozone at stratosphere is an unstable molecule made up of three oxygen atoms. The instability of the molecule allows the free oxygen atoms to react with hydrogen, nitrogen, chlorine and bromine.

Electronic leak detector works on the principle that when halogen vapour is heated, it increases the positive ion concentration thereby increasing the conductivity of the air sample drawn between the ion emitter and collector (anode and cathode).  This increase in positive ion conductivity is magnified using electrical circuit so that audio or visual signal is produced.

This is the reason vacuum test not an ideal method for leak detection system.

After burnout the suction line filter drier is used to prevent any acid in the system from returning back into the compressor suction.

If large vacuum pump is used, vacuum in the system drops very fast causing the evaporating water to cool and freeze rapidly. This results in removing water from the system more difficult.

Low pressure appliances uses a refrigerant with a liquid phase saturation pressure below 45 psia at 104°F.

Saturated refrigerants have a specific pressure rating at a specific temperature. If both these parameters are measured, correct refrigerant can be determined by looking at pressure-temperature chart