Heater not working on house battery - 2014 Jayco Greyhawk

[Dot&Sam]

We are in the 4th year of using our 2014 Jayco Greyhawk 31FS motor home and all of a sudden we are having trouble with the heaters...just in time for us to go camping in the Rocky Mountains. We have an electric Aircel AC/Heat pump (model 48004-969) and an Atwood Gas Furnace (model 8500-IV series). The thermostat is a RVP 8530A345, RV Comfort.HP. I just replaced it hoping that this was the problem but there seems to be no effect.

Both have worked fine till now and still work fine if we are plugged into shore power. If we are working just on the house battery neither of them turn on and stay on for more than 1 minute then shut off. I don't recall having this problem before. I checked circuit breakers and fuses and they seem fine. The problem isn't affected by having a fully charged house battery or less than fully charged.

Any ideas would be helpful.

Thanks,
Sam & Dot

[RetiredOne]

If the furnace works on shore power, but not on battery, are you sure the battery is fully charged. Have you taken an actual voltage reading of the battery?

[2edgesword]

I'm not 100% familiar with heat pumps but I'm pretty sure it is a 120V appliance so it's not going to work off the battery alone (possible an inverter but I doubt it). The furnace should work on propane and 12V DC. If it's not working when you're not plugged into shore power then there is either a problem with the battery (as mentioned) or possibly a fuse between the battery and line supplying power to the furnace is blown.

[Trapper2020]

X2
Check your house battery. Sounds like it is dead. With no shore hook up there is a minimum voltage required to start and continue running the house furnace. The heat strips and AC only works when hooked up to shore power. Safe travels

Enjoy the journey

[DavidJay]

It’s not the furnace. The furnace has 12v controls, so it “always” works on 12v, even when plugged into shore power.

This is almost certainly a battery or power distribution (wires, fuses, etc) issue. Check the voltage at the battery and at the distribution panel.

[Jagiven]

X+1 sounds like a discharged battery. There is a minimum voltage for the furnace fan to start. Lights will still work, but maybe starting to dim. If you have a multimeter, I recommend checking the battery voltage with the shore power disconnected. Ideally for an hour or two. A fully charged battery will read 12.6 volts, once it stabilizes. A depleted battery will read 12.0 volts. A freshly charged battery may read 12.6 volts for a short time once it is off the charger, but will drain down relatively quickly.

[2edgesword]

Originally Posted by DavidJay

It’s not the furnace. The furnace has 12v controls, so it “always” works on 12v, even when plugged into shore power.

This is almost certainly a battery or power distribution (wires, fuses, etc) issue. Check the voltage at the battery and at the distribution panel.

The furnace always works on 12V but the 12V can be supplied by the battery or the converter. If it's working on shore power and not on battery that would be an indication that the converter is working (supplying 12V) and there is a battery problem (either battery or fuse between battery and furnace).

[memphis02]

I do not have the same setup as you, however, on mine; there is a heat pump and gas furnace setting. Could you be set to use heat pump and 'that' is what isn't turning on? Does the warm air come from the ceiling or from vents in/near the floor? You haven't mentioned if any other 12v devices are experiencing issues, so I assume you've tested other things and they're working fine?

The alternative to the above is that there isn't enough voltage/amperage to run your furnace when on-battery; in that case a load-test of the coach battery should be informative, but I would expect other items to have issues, too if this were the case.

[Dot&Sam]

Thanks for the tip. It turned out to be the "sail switch" in the blower for the heater. The sail switch tests for a minimum flow of air out of the heater to the outside and it is intended to prevent buildup of un-combusted gas in the unit. If unchecked then this could cause a fire. I worked with my local rv repair shop to buy the $18 part and then it only took about 30 minutes to replace. Since then the propane heater and blower works fine! In fact we just returned from a 1 month trip to MT, WY, UT and CO.

[msherw]

Great to hear you got it fixed. The sail switch is usually the culprit. Here is a great video on RV furnaces.

https://www.youtube.com/watch?v=N-zqTLjG7qA