Heater and Air Conditioner

[Jeb]

Greetings to all A/S'ers...
Now for my problem. I have a 2000 Land Yacht that had a sick dash a/c. The a/c was fixed but now I have a different problem. When I put the climate control on "cold" and "vent" I get hot air through the vent. Changing the cold/hot mixer doesn't seem to help. When the a/c is on "cold" and "max" I get somewhat cool air. I know the a/c is working because I can feel the low pressure hose by the condenser and it's REALLY cold. I think the hot engine air is mixing with the a/c and making the air warmer. I have ACME controls. Has anyone experienced this problem? Is there something I could check and possible fix myself? Thanks all.