Furnace 12 volt and 110

[drifterranch]

All literature shows that the furnace should run on 12 volts only. Tonight I was going to run the furnace for a while working in the RV. It would not come on. I turned on the AC 110 breaker and it came on. I can only assume since the AC unit has a heat pump the thermostat must have a 110 feed to tell the thermostat to run the furnace Can anyone provide insight. All my previous RV I could run the furnace off of 12 volt only.

[TucsonJim]

My furnace will run on 12v. There are two likely scenarios which caused this.

1. You're battery disconnect is turned off. This prevents the furnace from getting 12 volts from the battery. But when you turned on the breaker, it activated the converter. The converter provided 12v to the furnace and it powered up.

2. the battery voltage was too low and wouldn't run the furnace. Once again, when you activated the breaker, the converter turned on and powered the furnace.

[drifterranch]

When it did not come on at first I thought the same thing. I checked the breakers and the converter was on. I had full voltage to the batteries and the 12 volt switch was on. I guess it may have been a coincidence it came on when I turned on the breaker. I will do more checking today. Thanks

[howson]

When it did not come on at first I thought the same thing. I checked the breakers and the converter was on. I had full voltage to the batteries and the 12 volt switch was on. I guess it may have been a coincidence it came on when I turned on the breaker. I will do more checking today. Thanks

What TucsonJim wrote in post #2 was exactly my thoughts when I read your initial post. Your battery is likely the culprit--may measure fine without a load but when called to provide power it may drop below the 9.5v referenced in the Suburban Service & Training Manual (pic below is from that manual).

If your battery turns out to be fine then I'd suspect an intermittent problem. Perhaps the sail switch was stuck closed or you have an intermittent ground connection. But start with the battery--my .02 is on that as the issue.

I know you'll let us know what you find!

-Howard

P.S. In addition to the picture below, there's an article posted on the RVDA.org site in their RV Technician magazine. Not sure if it's helpful, but it does focus on power as the #1 thing to check. You can read it yourself here: https://www.rvda.org/App_Themes/RVDA...Tech_FINAL.pdf

[drifterranch]

Thanks for the responses and the article. I went back through everything and checked voltage, fuses. made sure converter was on and 12 volt switch. the coach sat all night. It worked fine when I tried yesterday. We will be heading to big bend next week so ti will get a work out I am sure. I will update the post if it happens again. I hope it was low voltage that is an easy fix. Thanks again for the help.