Air Con UV Dye- The chances are that if the a/c needs re-gassing then the old gas has leaked out. As the gas is invisible the only way to find the leak is to look over the A/C system with an ultra violet light for the residue left by the dye where the gas is escaping. The dye can only be added when the gas is full so must be added at the time of a re-gas.
Unfortunately if you have a re-gas without the UV dye and it leaks out there is no way to trace the leak and you will incur the added expense of having to re-gas the system again in order to add the dye.
Air Con Sanitiser-A/C systems are a known breeding ground for a number of germs. This sanitiser cleans the system and also eliminates any nasty odours from the a/c and heating systems.