No power to RV Furnace or Thermostat

[henri328]

Dear RV.Net

I have a 2000 National RV Seebreeze 1340 class A motorhome. In general, we really like it.

Recently, the furnace simply quit. It will not restart. there is no clicking or power light illumination on furnace control panel. No breakers were tripped, no wires are loose.

On the Duo-therm thermostat, there a terminal board at the top (after removing the cover) On the left is one rated at +7.5 V. then there are terminals for the various units (heat , ac etc) and ground. There is 0 V between the +7.5 terminal and the GND terminal, so it seems that no power is coming to the thermostat.

I checked the battery control centre and pulled the fuses in that area and they all seem fine. I have 12DC for the other appliances such at the water pump etc.

There is enough propane as the stove lights etc.

I do not know what else to check. Can anyone think of what might be the problem?

The furnace is a Hydro Flame 8500-IV

Thanks for your kind advice,

Henri van Bemmel

[wa8yxm]

Furnace normally gets it's power from the house fuse box.. Then, at least on an Atwood, it goes to a circuit breaker (looks like an on-off toggle switch) that is on top of the blower housing accessible from OUTSIDE the RV (remove the cover) From there via a MOLEX connector to the control board and from there via a different pin to the thermostat, So if there is no power to the furnace, there is no power to the thermostat.

NOW.. Normally a bad control board would be suspect. but as I recall. not in this case but the switch/breaker is.. Check for power on the control board.

[dougrainer]

The power may come from the front roof AC. Access the filter of the roof AC and you will see a control board housing with wires. Usually, they run 12 volts TO THE ROOF AC board. They then transfer the power via the wall tstat wires to the wall tstat to power the wall tstat. BUT, there is still a separate 12 volt supply direct to the furnace. Have you checked the 4 wires the furnace? There will be a 12 volt RED positive and a Black 12 volt negative (ground). The other 2 wires (may be blue) are the 2 wires to the wall tstat. ONE of those blue wires will have 12 volt positive. IF you have 12 volt power to the furnace. Doug

[Old-Biscuit]

You have a blown 12V DC fuse......need to locate and test not just look at them

Also......remove outside access panel and check the CB/On-Off switch located on frame. See it it is tripped.

[Mandalay_Parr]

Do you also have fuses at your power dist panel?