The photo is the back of the refer, not the furnace.
Pop the cover off the thermostat. There should be two wires on a standard furnace thermostat. Disconnect one of them. Test to see if it runs. If it does not it is a bad thermostat.
If it runs locate the furnace access panel, inside the coach. Find make, model and post that information.
While there look for the thermostat wires. Should be blue in some makes. Disconnect one there and see if it runs.
Depending on model and version, there could be a time delay relay. It could be stuck.