Furnace screams until warm

[dellvostro]

We are dry camping up in Cheyenne where it's been in the 30's at night. The kitchen furnace under the dinette seat howls like a Banshee for a minute or two until it warms itself up and then quiets down. Only the dead could sleep through it.
I have had the cover off and there's nothing obstructing the fan and it seems to turn smoothly without binding. It almost seems like a dynamic vibration caused by cold sheet metal.
Has anyone had this noise problem and have any ideas for a fix?

John B

[rbbuscher]

I would try a shot of WD-40 on the fan shaft first.

[gcyeaw]

It is most likley the motor bushings. Mine did the same thing, Use a light oil on the motor shafts and bushings. WD-40 is not a lubricant, it will only quiet them down for a short while.

[rwoody]

what gardner said

they are not wore out just dry ...........

[dellvostro]

Problem solved! While opening up the sheet metal enclosing the fan motor in order to access the bearings for lubrication I discovered that the fan was conacting the inside edge of the opening for it in the sheet metal panel/baffle. A bit of tugging,tapping,swearing and re-alignment and it works like new!
By the way Bob, Gardner and Woody I also applied a bit of lubricant to the fan shaft for good measure and thank you very much for the replies, it was just the encouragement needed!
Now that three furnaces are operating satisfactorily would anyone care to venture a guess as to why the living room furnace is inop? Switch on thermostat is in "on" position, temp is dialed up, dash switch on, etc, but nada. According to diagram I have, it's breaker #10, wire #12 (red) in left front load center. Is that the one over the driver? If so I can't find that wire. I managed to get scalped a few times though.
All suggestions greatly appreciated!

John

[sfedeli]

Hi John,

There is a chance that you have a bad thermostat. One of mine was not passing 12V when in the "on" position and calling for heat. Try testing for voltage- one is normally always hot, the other one carries 12V to the heater when the thermostat closes. Most of the LP furnaces have 4 wires going to the control panel on the unit. One is 12V hot, one is ground, one carries 12V hot to the thermostat and one brings the power back from the thermostat when you need heat. In a perfect scenario- you would have three hot wires when the furnace is running and two hot when it is off.

[dellvostro]

Thanks Shane I'll check that thermostat and let you know.

John

[gcyeaw]

John,
As usual, check the ground wire. On my '78 thery were fastened by a screw thorugh the wood to the metal floor. This results in loose connections over time as the wood ages and shrinks.

As Shane said, check the voltages.

[dellvostro]

Gardner, thanks for that information. Is that the thermostat ground or at the furnace?
thanks again,
JB

[gcyeaw]

John,

That would be the furnace ground. It is one of the wires in the connector. You should be able to follow it back to the grounding point. There isn't any ground at the thermostat, it acts as a switch connecting the two blue wires together. There is a small heater element in the thermostat that works off the current drawn through the circuit. It is called the anticipator, and if set right causes the thermostat to shut down a little sooner. This prevents the temperature in the coach from varying too much.

If you disconnect the connector at the heater you can use voltmeter to check that the thermostat completes the circuit. Connect the black lead to the ground terminal and the red one to the single blue wire terminal. You should get 12 volts if the thermostat is calling for heat.