The bacteria Grows on the Evaporator.. Mainly due to lack of use.. It can be Killed of by an "antibacterial" spray or by using the A/C more often. To limit the growth you should run the A/C ALL year round..
A/C acts as a dehumidifier and clears that winter morning condensation in double quick time.. and in summer it cools you down.. So run it continually.
You only need to have the system Regassed if the system stops working, or there a significant loss of cooling performance.. The temperature of the Cool air in the middle of the centre vent should be around 4-8 degrees celsius, no lower..