BKmetz said:
Freon 134A systems usualy have to be topped off more often. I usually have my car topped off every two years.
Not good, your system has a leak and it should be found rather than just topping it off. Gone are the days of topping off your A/C every year or two.
If the air con works only when driving then one of 2 things is wrong:
1) the compressor can only move enough refrigerant when it is spinning at speeds above idle
2) there is only enough airflow over the condenser when you are moving
To test for 1, have a mechanic attach high and low side pressure gauges to the system and monitor the pressures both at idle and with the engine revved up to 2000RPM. Depending on what the gauges read this could be either low refrigerant or a bad compressor (or many other pieces of the A/C system but these are the 2 most likely for this situation)
To test for 2, check the condition of the fans when the A/C is on, that is, are both fans running, only 1, none?... high speed or low speed? Is this the same when it is working properly as when it is not? This issue could be a bad fan controller and/or bad fans