When the air conditioning is turned on no cold air blows and only hot air comes out.
Airconditioning on 1994 BMW 540i
If the air conditioning isn't putting out cold air the refrigerant is likely to be low in charge. The system will naturally loose some pressure over time but it shouldn't require constant topping up or there is a leak which needs to be investigated and repaired before just recharging the system. The system has a low pressure switch that shuts off the compressor if the charge is low to protect the components in the system.