My 2003 MPV A/C blow cold when we are standing still or going slow. However, once we get up to speed it starts warming up. When it is blowing warm it seems to blow humid air. Any opinion?

 

Sounds like your starting to get low on refrigerant, when your at a stop the amount of heat that can be transferred is low enough that the current amount of refrigerant can handle the load without tripping the high/low pressure switch but once you get going it trips the switch due to better cooling across the condenser and lowering the pressure below the trip point. Take it to a shop and have them check the system pressure, alot of shops will do this for cheap if not for free (takes 5 mins if that). When at idle does the compressor seem to cycle (on-off-on-off) often like every 3-5 seconds?

If anyone else has an idea chime in!! I am not an AC expert, I just go off of my experiences.

 

Just went through a lot of sh** with a/c because of stupid mechanic. Now I am an expert ;-) . 1./ Cold air /idle / warm air on Highway = means not enough circulation of Freon - possible clogged Drier/Evaporator OR clogged also Condenser . To stay away from huge expences - best you can do FLUSH A/C system . If it's not getting better - Drain system to recovery tank / replace Drier/Evaporator / check Condenser . And REFILL freon . Rergards
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One more thing - you may check your Gas/Mileage With A/C "on" and A/ C OFF . Clogged A/C system takes much more gas . You better hurry - clogged A/C system won't last too long .