Air Flow and the Condenser
The air conditioner's refrigerant receives heat from the cabin through the evaporator core. It then transfers this heat carrying refrigerant to the condenser where it is transferred to the outside air. It transfers this heat to the outside air and changes the refrigerant from a gas to a liquid through condensation. Without proper air flow, the refrigerant is unable to release this heat, and transfers it back through the system.
Fans provide air flow while the vehicle is at rest. Air flow through the condenser is vital for automotive air conditioning performance. If its fan is not operating or spinning too slowly, its poor performance will be more pronounced while the vehicle is at rest. This is because while the vehicle is moving, ram air is being forced through the condenser, transferring heat from the refrigerant to the atmosphere.