20 Most Recent Dometic 457915 Duo Therm Brisk Air Conditioner - Page 4 Questions & Answers

if it lines up it is only a flue or vent to exit exhaust or hot air

You may just need to upgrade to a newer duo therm. Check out Dometic RV Refrigerator Parts and Products for Sale he's got a couple.

Maybe unit is already satisfied. For unit to run in heat temperature set point must be above room temperature

Should be a fuse somewhere for that blower

Your thermostat is no good. Depending on the age of the unit, you might be able to replace it. Pull the cover off the bottom of the unit to expose the thermostat. If it is an older unit, you'll have a copper capillary tube that is connected to the sealed system and you'll need to take it to an RV repair shop to have it replaced because it is a mechanical t-stat and you'll need to break into the sealed system to replace it. If it's a never unit and you have wires on it, It's a matter of pulling it out and finding a replacement

Most thermostats operate this way. Instead of dropping the voltage a thermostat opens the circuit when the set temperature is reached, after which it closes again to redo the cycle again. The principle can be based on heat, time or pressure. The animation, if the GIF runs, shows the basic principle for a thermostat switch in a heater/geyser, but can be modified to operate via a pressure diaphragm as used in ovens and fridge compressor relays. Strip heats/opens then closes.

I would look for a wiring diagram in it by removing the electric panel covers and the look for power and control voltages.

check for a failed start/run capacitor take it to a motor repair shop for a test and diagnosis before spending money on a problem that may be a cheap fix