Furnace Trouble-Shooting

[steve dunham]

Originally Posted by ZachO

Well I'll admit I'm not quite sure what you're saying on a lot of this, but I'll keep checking stuff.

If the furnace calls for 12V for a few seconds then gives up, am I in a rush to test at the thermostat? Will there be 12V when I first turn it on, then it'll stop when the furnace fails to do anything?

Well, I'm taking another unadvisable step. It's fairly safe to assume that the wire from the power center to the thermostat didn't melt, and that the connections are still good, and that whatever shorted is in the furnace itself. I don't see a tiny spark causing a wire or connection that far away from the furnace to melt or break, though one last test I'll do is a resistance or continuity check on that wire.

Other than the electronics on the propane valve in the furnace, I've tested or replaced every switch, circuit board and fuse associated with the furnace, except the time delay relay. That's a $30 part. I'll throw $30 more at this thing, then if it doesn't run I'll decide whether to pay a technician or just buy a new furnace. I'm moving back in at the end of the month so it's time to get the camper functional.

Thanks for the help!

I would check the relay . Relays that are used to switch low voltage , low amperage loads have a tendency to have faulty high resistance contacts . N/C contacts are the worst because they are often held closed by a spring.
So even though the coil on the relay is good does not mean it works

[k0wtz]

in case this is shot White-Rodgers makes a low profile gas valve made for simple operation. it can mount any direction but upside down this is what I used on my v/c stove. matter of fact they mention for rv use also!

very simple in its operation uses a thermostat off the gas valve and a manual rotary knob for heat settings.

everything simple I think I spent 120bux or less!!!

bob

[mszabo]

My thoughts also on the relay.
As I said a quick test is to jumper the 12v wires on the relay feeding the motor.
Which will put 12v direct to the motor.

How it works, 12v into furnace(2 wires) 2 wires come out of furnace to thermostat. One is low voltage other is return to furnace relay.
As Steve said relay is normally closed. The low voltage heats coil in relay, which which closes to complete circuit. Allowing relay to close and sends power to motor and sail switch.

Getting the motor to come on is the first step. Until this happens in that order it’s not possible to get running.

First step check for 12v power to furnace
-power to thermostat which you said you have. Which means you have power to furnace.
- turn on thermostat, which sends power to timed relay. If relay is working, in about 15 to 18 seconds the motor will come on.

This has to happen before anything else.
If this doesn’t happens, then you start testing from there.

Which will be a problem with
No power to furnace, no power to thermostat ( bad board) no signal to relay. Bad thermostat or wire.
Power to relay no fan control. (Bad relay.)
Power to motor, no start (bad motor)

So, once you verify that motor is coming on in that order. You can go on to finding the problem as to why it didn’t fire.
Which will be,
Bad sail switch (possible )
Possible thermistor switch, not likely
Power control board, (possible if no spark or power to thermostat )
No spark control bd, possible electroid, clean adjust, test for continuity.
Bad gas valve, (not likely)
Bees nest in flue causes it to shut down
No gas, air in lines, dirty propane, dirty burner etc.

You can do this, and you will learn. If your like me and have more time than money. You will figure it out.

I had pm’d you my phone number, if you need to talk through it.
I see Steve jumped in to help, you can reach out to him also. He is sharp and a electrician, I think.

You can’t guess, think or assume, anything. You have to verify each step before you move onto the next.

Myself, I’d remove the unit and work on it on the Bench. And you may have to also, if you haven’t already.

[ZachO]

Thanks again everyone.

Ok, so mV at the thermostat is ok? I figured it would be 12V.

If I get it running I'll likely replace the thermostat anyways, next. I've never liked the Atwood thermostat. There's also some resistance along it, but maybe that's ok. Not sure. It reads somewhere around 2-5. It beeps fine on my multimeter, but does show resistance.

Anyway. Circuit board is new, sail switch is new.

Yep, more time than money, though I don't like how much time I have to spend on this thing between the fridge and other little things that always pop up. Oh well.

If I find more time I'll test the motor with a jumper wire. If it's bad, it's new furnace time. Otherwise the new relay shows up next week and I'll just test the furnace then.

One question on the multimeter, which I'm still learning, and no online tutorials seem to go into, probably because it's so basic:

When I'm testing for voltage in the camper, I put the red on the switch/relay/fuse etc., and the black to ground, correct? How do I know if something is grounded? I mean a screw in a cabinet isn't, is it? When I'm testing the thermostat, there's not much within reach to use as a ground. I can just barely reach the water pump, but is its metal body grounded?

[mszabo]

Test thermostat, put one lead on each wire. You will be checking voltage only.
Use low scale dc voltage.
If you show voltage, tells me you have 12 volt going to board/ furnace and is sending power to the thermostat.

Thermostat turned on, is just touching the two wires together. Sending that voltage to the relay.
Think of the relay as a switch. Its a low power switch connecting / turning on the high power Switch.
In this case, turning on the motor.

Putting the two thermostat wires together is the same as turning on the furnace.

[mszabo]

Forgot, test thermostat Do a continuity test, One lead on each terminal.
Turn on, will read to zero or beep. Set on beep if you have it.

Make sure when you install the relay you have the power turned off to furnace.
One spark could/will destroy that relay.
I suspect that’s what happened, when you said it sparked and didn’t work afterwards.

[gordon2]

Originally Posted by ZachO

...
Ok, so mV at the thermostat is ok? I figured it would be 12V.
...

You can ignore very small readings like a few millivolts. A reading of a few millivolts when you are looking for 10-15 volts is meaningless.

[steve dunham]

When you are taking your meter readings at the thermostat are the thermostat contacts open or closed ?

[ZachO]

Ive tried both. I think...

I’ll try again tomorrow to be on the safe side. Which should they be?

Pretty sure I’ve tested it all ways I can think of, open and closed for voltage, closed for continuity and resistance.

Thanks gordon, I wasn’t sure. On a lot of stuff I test, it switches to mV and the numbers jump around, often settling near 180mV...Which has made me wonder if I’m getting a good ground with the black probe. But when I test the fuse at the power center, it reads a steady 12.4V.

[mszabo]

https://youtu.be/GglKiv3Uxic

[mszabo]

https://youtu.be/cLDUrkL19Fw

Furnace operating on bench

[k0wtz]

take my word for it steve is the pro here if he cant help you no one can!


bob

[ZachO]

Thanks again. I had the furnace out all winter and if I can get away with not pulling it again, I'm not going to pull it. But if the relay doesn't fix things, it's got to come out either way.

I'll keep you updated.

[ZachO]

No luck still. May replace the thermostat just cause I’ll be doing that either way, but otherwise I shouldn’t spend more money without in depth trouble shooting. Of course the smartest thing would have been not to spend any money without real trouble shooting but...I really figured between the board, sail switch and relay, I’d fix it and have replaced all the parts that typically fail. I actually found a kit online that includes these parts and the limit switch as a rehab package.

For now I bought a Mr. Heater and that’ll get me through spring.

[k0wtz]

zacho we boondock so don't miss the furnace I don't think they are efficient anyway.

just remember to crack 2 windows about 1/4in

good luck

bob

[ZachO]

Thanks Bob. Yeah it’s hard to insulate and seal against the cold...then crack a window. Better than dying though.

I almost never plug in, but I have a solar panel to charge the battery after running a furnace all night.

Mr heater is good but I wish it had a lower setting. Either off & on all night to keep a nice 50, or on all night and 60 or higher, which is a little warm for me. Better than no heat at all though!

[ZachO]

Mr Heater doing his job.

[ZachO]

Well here’s where I’m at.

I pulled the furnace and tested these wires.



With all of them I get mVs, not V on my multimeter, jumping all over the place.

At the power center I get 12.8V on both posts of the fuse.

What do I do from here? Seems like no power to the furnace

[ZachO]

Well I’ll take the ridicule...

I think I very well may have been checking the wrong fuse all this time, though it’s hard for me to accept that it was something so simple.

Fresh eyes show a whole new perspective. My power center shows that the furnace is fuse #3. That’s what I’ve been checking...I thought.

For some reason it wasn’t till today that I remembered the first fuse is completely hidden unless you stick your head all the way under the dinette table. I’ve been missing that first fuse, starting my count from #2, so checking #4 all this time instead of 3.

The actual #3 was blown. Put in a new fuse and had 12.8V at those wires in the previous photo. Hooked it all back up...HEAT.

So my guess is that the original issue was the circuit board, causing it to keep clicking but not fire. The spark when I started poking around may or may not have killed the time delay relay, but it definitely blew the power center fuse.

So now...new board, relay and sail switch. Assuming the relay and sail switch weren’t necessary, they add up to about $70 of money either wasted or well spent on preventative maintenance, depending on how you want to look at it. $100 for the board.

Thanks to those who helped and reached out through PM.

Mr. Heater can go into storage!

[Byron Kinnaman]

Originally Posted by ZachO

Well here’s where I’m at.

I pulled the furnace and tested these wires.

Attachment 117835

With all of them I get mVs, not V on my multimeter, jumping all over the place.

At the power center I get 12.8V on both posts of the fuse.

What do I do from here? Seems like no power to the furnace

Are saying one meter lead on one side of the fuse and the other meter lead on the other side of the fuse? If so replace the fuse. You should read close to 0 with meter across the fuse.