On Monday, 27 July 2020 07:26:12 UTC+1, Jim GM4DHJ ... wrote:
so I said I wouldn't but I did.....I bought a can of gas and a hose with
a meter...connected the can without piercing it and connected the hose
to the schrader valve and the pressure was up in the danger red
area....I then started the engine and I could hear the compressor coming
on....so what could be the problem?... looks like I have wasted my
cash....suppose I should have pushed the schrader valve before I bought
the stuff....

To test any refrigeration system you need to know the pressure both upstream and down stream of the pump to verify it's correct working.

Eg non-return valves in the pump may be US.

Check that the condenser (cold bit)fan is running.

Gas loss IS the normal problem in automotive AC, the gas is lost on the compressor shaft seal, sometimes only when it's revolving.