Q: AC blows cold only when driving

Hi There, Based upon what you are describing it sounds like the AC condenser cooling fan is not working properly. As you are driving down the road, there is generally enough cool air blowing through the condenser without the need of the fan to cool. Once you come to a stop, this cool air blowing stops almost completely resulting in the need for the fans to come on. If they are not working properly, this will cause the AC to blow intermittently cool and warm as you describe. I would suggest checking to see if the fan comes on when the vehicle is sitting at idle. If you do not hear it come on periodically, then it may suggest you have a bad relay which could be causing it to work intermittently. I would recommend having this looked at as soon as possible by an expert from YourMechanic to avoid further potential damage.