Temperature Adjust on F53 chassis

If I have the A?C on and want to make it a little less cold, turning the knob just a 1/8th turn causes warm to hot aire come out in about a minute or so.

Just looked under the hood and found what I believe to be the vent control, which blocks or allows outside air to come into the cabin. Where can I expect to find the blend door?

Check to see if the blend door is operating.

Normal. On Motorhomes, unlike Automobiles, they use a simple on off valve, that either stops the 180 degree water thru the Heater core or allows a small or large amount of 180 degree water thru the heater core. Just opening that valve a little causes the heater core to go to 180 degrees. The only way to moderate the temp is to turn the AC compressor on and try to get a medium temp that is good for you. Automobiles, use a Blend door system to regulate the amount of cool and heat coming out the vents. Gas Motorhome systems are 50 years behind the times, unless you have a Diesel chassis or a more expensive Motorhome that has a better system, usually in $200,000 and up motorhomes. Doug