Furnace only works on gen set

[zero260in1]

Hello Gents

I have recently purchased an old 95 Winny 38 foot DP. The last two months are a blur fixing the hundreds of problems, lol

One of my last problems are in the furnace. It works great when I start the gen set, but when im on the inverter it just blows cold and doesn't appear to want to light, Bark up the gen and off it goes again.

Is there something that is "going away" and the gen set just makes up for it or something else you guys have heard about

Thanks in Advance

Rick

[zero260in1]

Heres a picture of its first trip for us

I have already removed most of the old blue vinyl, painted the front and rear bumpers, replaced the tires, installed a new stereo, put new shocks on the basement doors.

Started the trip in Calgary Alberta, went straight through the rocky mountains, out to the ferry and over to visit the parents on Vancouver Island. No baby steps here... final trip ended up being around 3000km

Its a 300hp Cummins with a 3000 series Allison. Ran great Climbed the hills like a champ


Half way through the trip, the heater core started leaking , so I bypassed it until I got home. Shortly after the alternator gave up so I taped a battery charger to the frame and ran the gen set all the way home, lol


Its got me hooked, but something tells me im going to spend a lot of time here figuring it all out

[dennis45]

The furnace requires 12V power to operate.
Sounds like you may have a house battery problem. Have you tested the batteries? When you are running the generator it is charging the batteries the same way as when you are plugged in to shore power.
When you shut the generator off and the batteries are no longer being charged, the furnace will not light if the voltage drops if they cannot hold a charge.
Have the batteries load tested and I think you will find your problem.

[spider13]

X2 on the 12v.

[elkski]

But if the heater fan blows there is 12V... but maybe not enough to light the furnace? I imagine it has a electric igniter? It sounds like you are quite the handyman and I am sure you will get a simple 12v issue fixed.

maybe they had used stop leak in the coolant and a previous leak came back?
For a handyman the alternator and heater core wont cast to much.

[briankstan]

You need to check the voltage at the furnace at the time the fans start up, they pull the voltage down and this won't allow the gas valve to open for it to light. I chased this problem around as well, and replaced several unneeded parts .

I ended up running new wires to furnace from the battery and got it so the voltage didn't drop below the needed for the gas valve to open.

this is why it'll work on the gen as essentially your inverter is passing a charge to the batteries so it'll hold the voltage needed but when only on battery I bet you'll see a drop. Hope that gives you a clue.

[Gary RVRoamer]

This is a classic low voltage problem in the 12v system. Apparently you don't have enough battery voltage for the furnace to operate until the generator powers the converter/charger which in turn boosts the voltage. Shore power would do the same.

The furnace requires 12v and requires a certain minimum fan speed before allowing ignition. Speed is determined by a "sail switch" which measures the amount of fan air pressure. If the voltage is low, the fan runs too slow and the burner won't light. It's really a very simple set-up.

Since you have enough power once the genset is running, the furnace itself is clearly OK. Your problem is almost assuredly weak house batteries.

[dennis45]

Originally Posted by Gary RVRoamer

This is a classic low voltage problem in the 12v system. Apparently you don't have enough battery voltage for the furnace to operate until the generator powers the converter/charger which in turn boosts the voltage. Shore power would do the same.

The furnace requires 12v and requires a certain minimum fan speed before allowing ignition. Speed is determined by a "sail switch" which measures the amount of fan air pressure. If the voltage is low, the fan runs too slow and the burner won't light. It's really a very simple set-up.

Since you have enough power once the genset is running, the furnace itself is clearly OK. Your problem is almost assuredly weak house batteries.

Absolutely, this is a 95 model. I'm sure the furnace worked for many years with the existing wiring so before you reinvent the wheel and replace wiring, check the obvious.

[elkski]

It may be a pressure switch Rather than a sail switch in the safety circuit?, or am I to old? There is Usually a overtemp, door open, flow switch ( of some type), and pilot light temp probe in the safety circuit before the gas valve can open. Some units have a flu fan that may run a silicone hose to a pressure switch to make sure it is flowing.
Running new wires may have allowed it to run on a lower battery voltage due to less line drop. but just remaking all the electrical connections for better contacts may have worked.
Check the silicone hose for cracking. Maybe cutting off the ends and reataching Will help. Check your house batteries electrolyte.

[briankstan]

the issue can still exist even with new batteries as well. I had 4 brand new batteries (6v) and was still having the issues due to old wiring. running new wiring fixed the issue for me.

Make sure your have a good ground wire as well. There is a fine line between when it'll work and when it won't. Mine would push the sail switch completely but sill won't light because the gas valve wouldn't open because of the slight dip in voltage that the fan motor would draw.

[briankstan]

here is my thread from when I was working through mine. it might help you some.

http://www.irv2.com/forums/f54/subur...es-218602.html

[zero260in1]

Thanks guys.

The coach batteries read 12.4 static with no load. Then the fans click on and they drop to 12.2. Burner won't light.

Fire the gen set and they light up within 30 secs.


After using the coach for a few weeks I feel the coach batteries are in pretty good shape so the wiring suggestions are interesting. When it stops raining I'll go check the wiring.


What is concerning or in the back of my mind as a potential problem is the inverters performance. When the coach is on shore or gen all 110 outlets work on the coach. When I'm on house batteries with the inverter switched on , it appears only half of the outlets are live. Not knowing how many channels the inverter is capable of , and not knowing motorhomes at all maybe it's normal ?
Thoughts?

Unless these furnaces entirely run with 12 volts, and that eliminates the inverter completely.


What a great forum , thanks a ton.

[mel s]

Originally Posted by elkski

But if the heater fan blows there is 12V... but maybe not enough to light the furnace? I imagine it has a electric igniter? It sounds like you are quite the handyman and I am sure you will get a simple 12v issue fixed.

If the battery voltage is low enough the fan will run but it may not spin fast enough to close sail switch to close.... if the sail switch does not close, (completing the circuit to the gas valve), the gas valve will not open and the burner can not fire.

BTW, I also wonder if the OPs furnace only works when the generator is running or if it also works with shore power??
If so, as others have said, the his problem is low house battery power.
Mel
'96 Safari

[zero260in1]

Originally Posted by briankstan

here is my thread from when I was working through mine. it might help you some.

http://www.irv2.com/forums/f54/subur...es-218602.html

How did you run a new wire? Were you able to fish a new one through with the old one ? What was involved to pull this off .

Thanks