The gas charge will depend entirely on the length of piperun, number of bends etc.

You might have a problem with the Expansion Valve? Its not common, but it can cause theses problems that you mentioned?

Luckily, you can pump the system down and just change the power head, so its not a massive job?

If you can get the CONTRACT NUMBER off the serial plate, I can see if it was one of my commissionings and dig out the paperwork for you?