furnace problem.....

[norbert]

during chat time last nite ken johansen mentiioned his furnace wouldnt fire... the members kicked it around and came up with the following:
1 fan not running fast enuff-plug in univolt to check
2 bad sail switch- sail switch and limit switch are in series b4 power gets to valve.....
3 oil bearings on fan and motor-thats if they are not oil less

i woke up thinking about it... i have a hydro flame excaliber in my rig, and looked at the book i am troubled by the fact that there is no air filter-just a way to make a cheaper unit...i dont know if kens suburban furnace is the same, but his 75 furnace has had 28 years to build up dirt on the vanes in the squirrel cage...which would also diminish air flow velocity and cause the sail switch not to make...just my 2 cents worth...fwiw...
norby

[Ken J]

I did go out to the trailer this morning - there is voltage to the furnace, but could not check the thermostat because it is rivited to the wall - did not bring my drill with me. Could not get to the fan without surgery, so I figure I'll just wait until next time I have it over to the house. Tried to take a voltage reading at the thermostat, no voltage there, but not sure there is supposed to be voltage there.

Anyway, thanks for all your help - when I get if figured out, I'll be sure to let you know

Ken J.

[norbert]

ken, if your stat is calling for heat, the fan will come on..

[Ken J]

Sounds like I've got a bad stat then

Ken

[norbert]

dont write off the stat yet you should have power at the stat if you have power to the furnace

[Ken J]

Hmmm probably need to get someone to look at it......

[nickcrowhurst]

Ken, the thermostat is just a switch, so there will only be a potential difference (voltage) between the internal contacts when they are open. (when the thermostat is turned right down). To try to isolate the problem, I suggest:
1. Check for 12v on the ground side of the limit switch to make sure power is getting through the sail switch and limit switch. If not, then there is a defect in either the limit switch, the sail switch, or the fan is not running fast enough to blow the sail shut.(Low battery voltage, possibly)
2. If you have 12v on the ground side of the limit switch (between this side of the switch and ground), then turn the thermostat right down for a few minutes, then turn it right up, while looking through the inspection hole at the igniter. If you get a good fat spark arcing away for a few seconds about 15 or so seconds after the blower runs, your igniter is probably OK. It is then possible that the gas valve is not opening. The valve is not expensive. If you don't get a good long fat spark, your igniter may need replacing or servicing. The other possibility, which I suspect may be the case, is that the igniter board is defective. I have replaced the boards in my furnace and refrigerator with the Universal Ignition Boards (UIBs) from Dinosaur. They have fuse protection, are soldered both sides of the board for vibration resistance, and make 3 ignition attempts before cutting out, if I remember correctly. They are about $120, and in my view are a great investment, even before the original equipment fails.
In case there are any newcomers reading this, I should point out that propane and electricity are a lethal mixture. If in doubt, leave it to a trained technician. Good luck. Nick.

[norbert]

"once you figure it out, the instructions make sense"

[Ken J]

Thanks again - I'm going to print out your explaination and go from there........


Ken J.

[JimC]

Ken,

The picture is a wiring diagram of the NT-22 in my 67 TW. If it's not readable I can email an Acrobat Reader file.

You should have 12vdc on one wire of your thermostat, but you may have to ground your meter on a light fixture or some place where you can get to the (-) white wire in your 12 volt system. If your heater is wired like mine, you must have 12vdc to the Stat. The heater works like this:

The Stat closes to start heater. 12vdc is applied to the Fan Switch coil through the normally closed Heat Limit Switch. Ten seconds later the Fan Switch closes and the motor starts. Air flow closes the Sail Switch, which allows current to flow through the Gas Valve Solenoid and Air Limit Switch. Now your igiter should light the burner.

If the fan runs you know that half of the proces is ok. If not, the problem is in the wiring, Stat, Heat Limit Switch, Fan Switch, or Motor.

If the Fan runs and the heater doesn't light, the problem is the wiring, Gas Valve, Air Limit Switch, Sail switch, or the igniter. If the 12vdc connection is reversed to the heater, the motor will run backwards and probably won't open the Sail Switch. Is it blowing air out the heat vents?

Hope this helps.

[nickcrowhurst]

Jimc, we don't know how modern Ken's furnace is, but mine (1988) is very different to your diagram. Some parts are missing from mine (e.g air limit switch), and mine has an electronic board for sophisticated control. I wish mine was like yours! Let's hope Ken is getting on OK. Nick.

[Ken J]

Hello Jim........

Thanks alot for the diagram. I suspect mine is similar (its a 75). I printed out your diagram - next time I go to the trailer I'll check it out.

How is your trailer restoration going?

Ken J.

[JimC]

Ken,

The TW is up on ramps and the skin off the belly. Things are in pretty good shape, but the insulation is gone. Someone was in there before me. I need to go back under and drill out the revit studs. For the most part I just drilled off the heads before removing the skin. I plan to use sheet metal screws and stove washers to reinstall the skin.

The black water tank is out. I have had a new pan and mounting brackets made. I will paint the frame that I can get to with POR15 before putting it back together.

I'm replacing the heater which was under the sink. The new heater will fit under the stove, and open up space under the sink. I will have to cut new vent holes in the skin. I will cover the old holes with an access door and put the shore water connection inside the door. All the cabinetry will be rebuilt in the process.

See ya soon,

Jim