On the coldest night, the furnace dies! Help?

[parnelli]

Hey everybody-

Murphy has struck again! It's 2 outside here in Chicagoland and the furnace just died at 10:45. I've got an electric space heater for the bedroom to make it thru the night, but will have to make repairs ASAP in the morning.

I took a crash course on furnace repair- and I think that what has happened is the blower motor has died.

IF I can yank the blower housing and get a replacement motor from Grainger, it looks to run about 100.

The furnace is old- I'm guessing 15 years.

1)With the price of natural gas, should I just ditch it and get a new one all together? Is the savings enough to cover the cost? Heck, I don't even know what it'd cost at this point.

2)If I fix it, does anybody have experience doing this? All the stuff I saw online referenced the motors being 230v, and I'd just as soon not kill myself on this(literally!)

As always- you guys are great- thanks in advance!!

UPDATE: midnight: After some reading I learned that 1980's furnaces have two speeds. 1)Fast for air conditioning and 'fan on' switch, and 2)low for heating. I forget the website where I saw it, but someone suggested seeing if the blower would spin if the fan on switch is ON.

It spun with the switch set to ON. As soon as I went back and tested the blower with the fan set to auto (which should be low) the fan moves about 2 inches, humms and stops.

Here's what I can see when I remove the control cover:



When I think it's on High, the relay on the left switches and everything works correctly. When I think it's on low, the relay on the right switches, the motor moves 2 inches, humms, there is a blue 'flash' inside the relay and the motor stops.

So...is the motor dead and the relay "untrips" because of it, or is the problem with the relay.

If it's the relay- is it just the relay and I can go to Grainger and get one, or do you think it'll be the circuit board itself?

If nothing else, it seems as if I keep the thermoset set to "fan on" that I can have heat tonight. Just not sure if I feel comfortable sleeping

Sorry for all the questions- thanks again.

[stewchi]

Last year my furnace went out in the middle of winter, it was a different problem, the flames would start up then turn off, but in the process of trouble shooting I learned a few things. All modern forced air system have a high setting for cold air and a low setting for hot air (hot air is lighter and easier to move) really modern furnaces have 4 speeds (I am not sure why).
I ended up replacing the computer board on my furnace and cleaning around the burners and sensors pretty good. It appears there are several safty settings that will turn off the gas (Flame Detector, Pressure sensor for exhaust, etc).
When talking about the problem at work a buddy of mine told me he had to run his furnace with the fan set to ON so it would run at high speed, the relay was bad and would not run the fan at low speed. At lunch we headed over to this HVAC supply place in Naperville to pick up a new blower for his furnace. A lot of the time you can call the store with the name of the furnace and name of the control board maker (not always the same name) and they can tell you if they have a replacement part. While at the store I saw a couple people come in bringing thier entire blower assembly and asking for a match to replace it.

Unless you are not comfortable doing the work I would not get a new furnace. Once you replace the board and the blower (not sure if you need to do both) you will have replaced nearly everything in a furnace that can go bad, another thing I learned monkeying with my furnace is a lot of HVAC work is custom. On mine the original installer made some kind of mounting plate out of sheet metal to mount the control board. It did not fit the foot print of the new board so I had to re tap it, re solder a few connections on the wiring between the board and humidifier etc. I guessing that a new furnace would also need custom sheet metal work to hook up all the ducts. I bet that is all custom to the model number of the furnace and the house.
Bedsides if you get a new blower you can always sell or use the old one for a down draft table or air filtration.

[BobSch]

If nothing else, just turn the fan on until you can get it fixed or replaced... At least you'll have heat!

I'd seriously look at replacing the whole furnace. With gas prices going nowhere but up, a high-efficiency unit will pay for itself in not too many years.

[parnelli]

FINISHED- figured I'd post the conclusion in case any one searches for 'furnace' in the future.

I found the model number of the board and googled it. The OEM board was about 200 and since I wasn't certain that was the problem, I held off.

Upon further reading, I found out that the relay's are normally closed. By removing power from the transformer (blue or red above pic- top right), - it would open and the fan should start. It did.

Then when I went looking for a cheap place to get a board, I found www.icmcontrols.com which is an aftermarket manufacturer of the things. Took a bit to find a place locally that would sell them retail, but with a bit of fibbing as to where I am employed, I got it for under 60. FYI- you can by control boards on ebay too, but obviously have to wait for shipping.

After all is said and done, I only had no heat at all for a night- and it seems to be a-ok after only $60.

[Jim-Iowa]

Glad to see you have it back up and running.
That will give you some breathing space.
I know Cost of living is pretty high in the Chicago area.
And at that age effiecency may not be that great.
You may want to look into a new high efficency furnace?
The savings in fuel cost will normally pay for it in less than five years.

[stewchi]

To bad you didn't get a new blower, to build that down draft table

[JimD]

It isn't too hard to get a quick handle on what you can save. Your existing furnace is probably about 70% efficient - about 70% of the gas you buy turns into heat into your house. A new one will easily be 80% and can be as high as 95% or so. If you go past about 85%, you vent the unit in plastic pipe out the side of the house, the exhaust gas is too low on temperature to reliably drift out the normal stack. Last time I looked 85% is about where the price begins to take off too.

If a savings of 10% to 20% of your heating bill will pay for a new furnace, it could still be something to start saving up for.

Jim

[rfisher7381]

Keep in mind that there will be Federal energy credits or rebates starting in 2006 and running through 2007. I don't think the final credit or rebate amounts have been issued but for an energy efficient furnace it will be around $300.00.