Hydro Flame 8500 series furnace

[Camper44]

Hello all,
I have a hydro flame 8500 series furnace, the thermostat has an on-off switch,and a 3 position fan switch, low,auto and high,the furnace will not light on the auto setting but if I switch it to the low setting it will fire up, then shut down after reaching temperature. I turn the power off and fan switch to auto,then have to repeat the process to fire back up again when it chills back down again, any input would be appreciated. Thank you

[dougrainer]

The OP just joined. The OP needs to understand to ALWAYS post
1. Year and Model RV
2. Brand and Model of the appliance, in this case Roof AC and Furnace
3. Without that info you cannot get accurate help
4. You would not post on an Auto forum, my car runs bad and not state year Brand and Model of auto. Doug

[dougrainer]

Someone probably replaced the OEM tstat with a aftermarket home type and just used the lo fan as the return to the furnace because they did not know how to wire it. If original, then someone has miswired it. Doug

After reading the post again, IF that tstat does NOT operate the roof AC at all, then that Tstat is aftermarket and is not wired correctly. Does the wall tstat state HEAT and COOL? A COOL only tstat the temp thermistor or bi metal spring is wired/coiled in reverse than for a HEAT(furnace Tstat) only tstat. The OP needs to state what Brand is listed on that wall tstat.

[Dutch_12078]

The fan speed switch is for the A/C not the furnace. If switching it affects the furnace, I'd suspect a possible wiring issue at the thermostat.

[Lwiddis]

Only three identical posts? Try 12 more.

[mchero]

Sounds like the wrong stat. No fan speed on that furnace.

[enblethen]

Make and model of thermostat?

[larry_cad]

What happens when you switch to "High"?