Diagnosing Fridge and Freezer Gas Faults – Hints and Tips

Hi all

I am just starting to get into repairs of fridges and freezers and would like some hints and tips on what signs to look for which would indicate a gas fault as opposed to thermostat.

Also while I am on the topic – what training/qualifications etc do you need to be able to re-gas a domestic fridge/freezer. Where is the best place for training? etc

Thank you

Jem