Furnace / inverter problems

[andy29847]

I love electrical mysteries - NOT. I'm hoping some of you can lead me out of the dark on this one.

3 weeks ago, it got cold and I set my thermostat for furnace (duo therm 5 button - surburban 42,000 BTU). The furnace did not come on, not even the fan. I fooled with the thermostat a little without success. I left the thermostat set on furnace and 70°. Three days later, it started working.

The furnace worked as normal the rest of the week. Then we packed up and went home. The next week, we were on the road again. The furnace worked all week in the new campground. When I packed up to go home after this week, I started the generator to power the coach, thinking that we would need the furnace on the way home. The furnace did not work on trip.

I also noticed that the tank monitoring board wasn't working. When I got home, I checked all the breakers and the DC fuses. All were good. When I reset the inverter (Freedom 458), the tank monitoring board started working again. When I turned on the thermostat / furnace, the board quit working and the furnace didn't come on. I tried this on shore power and on the generator with the same results. Durn! This is confusing. One other note, the water pump works when the monitor board is not working.

I'm thinking I need a nap and a visit to my psychiatrist before I start working on this again. Youse guys got any ideas?

[wolfe10]

Andy,


A lot of "crossover thinking" about what works on 12 VDC and what works on 120 VAC.


The furnace is 100% 12 VDC. While driving, your alternator supplies the batteries, so absolutely no need to run the generator.


I would start by cleaning and tightening the connections at the house batteries.



After that check voltage at the batteries when the "no work" occurs.


Then check voltage at the appliance that is not working.



That under $20 digital voltmeter IS YOUR FRIEND.

[andy29847]

Originally Posted by wolfe10

Andy,


A lot of "crossover thinking" about what works on 12 VDC and what works on 120 VAC.

The furnace is 100% 12 VDC. While driving, your alternator supplies the batteries, so absolutely no need to run the generator.

I would start by cleaning and tightening the connections at the house batteries.

After that check voltage at the batteries when the "no work" occurs.

Then check voltage at the appliance that is not working.

That under $20 digital voltmeter IS YOUR FRIEND.

Thanks for the coaching. I've got one of those digital volt meters and I've used it some. I have already checked the batteries (but not load tested). Everything 12v and 110v works in the coach except the furnace. It's not real easy to check the furnace for 12v. The thermostat lights up. Unfortunately, the control module is hard to access.

The fan doesn't come on when I try to turn on the furnace. That would normally indicate issues with the thermostat or the control module. While testing the furnace on shore power and generator power, I noticed that the tank monitoring panel wasn't working either. Experimentation found that if I reset the in inverter, and the thermostat was off, the tank monitoring board would work. After the inverter reset, if I tried to turn on the furnace, the monitoring panel quit working. To my knowledge, the 2 components do not have anything in commen but the ground circuit. I went through the power panels tigtning neutrals and bonds. I tested the 12v fuse strip. I'm baffled. I guess I should troubleshoot the furnace until I get it working, and then see what the monitoring panel is doing. FWIW, even when the monitoring lights aren't working, the pump works. Also, the furnace is on one 12v fuse, the pump and monitoring panel are on a different 12v fuse.

[andy29847]

Making some progress. I have been testing on 2 12v circuits. The first one is labeled furnace/water heater. The second is labeled monitor board/water pump. I couldn't understand why the 2 were interacting with each other. Then I found that the monitor board was wired to the furnace/water heater circuit. That circuit goes dead (in the coach, not at the fuse panel) when I turn on the furnace. I moved the monitor board over to the water pump circuit so I don't have to deal with that mystery now.

The furnace still will not come on. The wire that leaves the 12v fuse strip is spliced somewhere and I need to find it. I expect it will be somewhere in the furnace compartment.

[andy29847]

Success! I found my bad connection in the furnace compartment under the refrigerator. The work looked like it was done at the factory. If so, they ran out of wire connectors that day. I found 4 wire splices (4 different circuits) where the wires were twisted together and then wrapped with vinyl tape. The bundle of wires was then strapped to the floor. It had been there a long time. The wires were corroded and the ends were breaking off. All this was on the right side of the furnace as you look in the compartment. I re-spliced the wires. I soldered the ends together. I also stored the ends up off the floor. These connections should have been made with an automotive style connectors. I'll make good on this another day.

[Hayduke]

Originally Posted by andy29847

Success! I found my bad connection in the furnace compartment under the refrigerator. The work looked like it was done at the factory. If so, they ran out of wire connectors that day. I found 4 wire splices (4 different circuits) where the wires were twisted together and then wrapped with vinyl tape. The bundle of wires was then strapped to the floor. It had been there a long time. The wires were corroded and the ends were breaking off. All this was on the right side of the furnace as you look in the compartment. I re-spliced the wires. I soldered the ends together. I also stored the ends up off the floor. These connections should have been made with an automotive style connectors. I'll make good on this another day.

congrats on finding the problem!

It seems you're already aware soldering is not ideal for this application. A crimp connector, properly installed, is preferred in environment subject to vibrations, ie driving down a highway. You might also want to use some heat shrink tubing.

[andy29847]

Originally Posted by Hayduke

congrats on finding the problem!

It seems you're already aware soldering is not ideal for this application. A crimp connector, properly installed, is preferred in environment subject to vibrations, ie driving down a highway. You might also want to use some heat shrink tubing.

I would be curious how these connections were made in other campers. FWIW, I used wire nuts filled with di-electric paste over the soldered connection (butt splice).

[Mule Skinner]

Nice work Andy
I’ve been having some mysterious issues with my control panel as well.
I’ll look in the same area you found your bad connection as soon as I get my coach back from paint repair.
Thanks for sharing,

Dan

[Hayduke]

Originally Posted by andy29847

I would be curious how these connections were made in other campers. FWIW, I used wire nuts filled with di-electric paste over the soldered connection (butt splice).

I've always thought wire nuts were appropriate in household wiring since it's not subject to the vibrations of driving on a highway.

AFAIK, for auto, marine, and aviation, a crimp connection with adhesive lined heat shrink tubing (they make the crimp connectors with the heat shrink as one unit) is the preferred method to join wire.

If you installed the wire nut well, ie strong connection AND wrapped in tape to mechanically secure it, you are likely fine. The problem is, if the connection starts to vibrate loose, you get a tiny little gap between the wires. The connection still works, but then you have a tiny little electrical arc through the air. That causes a LOT of heat. Eventually the wire nut melts and a fire starts.

Am I trying to scare you? Maybe a little
I'd been involved in discussions of this topic before. It comes up often on classic car forums.

If you are going to work on electrical yourself, you should invest in a crimp tool and the correct dies for your connectors. I think I spent $40 for mine, and it's served me well for many years. Do NOT get a crappy crimp tool. You want one that ratchets and does not release until the crimp is complete.

This video goes over crimp vs soldering

https://www.youtube.com/watch?v=faLn-SjVfwY

[Alpine36]

Yep, agreed that wire nuts have no business in automotive applications.
I've been slowly eliminating every one I find. I use quality automotive butt connectors with heat shrink and the Thomas-Betts crimper shown it your video. Never had one failure in 30 years of building/servicing a large fleet of service trucks for our municipal electric utility. Bucket trucks, digger derricks, Vactors etc...all subject to extreme conditions.
Ida been fired for using wire nuts or scotch locks on anything with wheels.

[cavie]

Originally Posted by andy29847

I would be curious how these connections were made in other campers. FWIW, I used wire nuts filled with di-electric paste over the soldered connection (butt splice).

All connections are made that way throughout the industry. It's called piece work. Get 'er done. Just the way it is. FYI There are two 12 volt circuits involved with the furnace. A 12 volt large supply for the fan motor and a different smaller 12 volt supply shared by the WH and fridge as you found out for the control circuit. Taping to the floor is the builders way of securing them from vibration.

[andy29847]

Crimp guys, thanks for the advice. It is good advice. In my case, I needed to finish the repair, and I used what I had at hand. I've already said that I will probably revisit the work. When I do, I'll be using automotive style connectors that provide for easy disconnect. Until then, the repair I made is waaaayyy better than what I found (that lasted 19 years).

[andy29847]

Originally Posted by cavie

All connections are made that way throughout the industry. It's called piece work. Get 'er done. Just the way it is. FYI There are two 12 volt circuits involved with the furnace. A 12 volt large supply for the fan motor and a different smaller 12 volt supply shared by the WH and fridge as you found out for the control circuit. Taping to the floor is the builders way of securing them from vibration.

HAHA - I was a telephone man for 42 years. I've seen some things done that had to be harder than doing it the right way the first time. Some guys would do anything to keep from having to climb a pole again.

[Hayduke]

Originally Posted by andy29847

Crimp guys, thanks for the advice. It is good advice. In my case, I needed to finish the repair, and I used what I had at hand. I've already said that I will probably revisit the work. When I do, I'll be using automotive style connectors that provide for easy disconnect. Until then, the repair I made is waaaayyy better than what I found (that lasted 19 years).

You're probably gonna be fine

I'm a bit anal with electrical stuff. I use wire nuts in my houses (we own rentals), but I always tape those too.

I wasn't trying to admonish. Just wanted to put the info out there for those that will come read this when they are troubleshooting their issue.