Most dash temp controls , are a blend air door, that mixes hot air though the heater core with outside air to control the temperature.
Evans and Denso are common manufacturers of the units installed in motor homes.
Do you see either of these names anywhere on the unit?
If you find a name then maybe the web sites can provide repair advice.
Evans Tempcon, Inc - Service Parts
HVAC Systems | DENSO Heavy Duty
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.