Need help from a HVAC Furnace Expert

[jim]

I have a Day & Night "Plus 80" furnace that is about 15 years old. In general, the thing is in good shape and I've kept it decently clean (lie).

Problem: Heater turned on, gas fired, and the blower did not. I would expect the fired furnace to not fire up if the blower is not working, but it did. Yes, house stunk for a day. Yes, I'm surprised the house did not catch on fire. It timed out luckily and all is OK.

Question is: Is the blower most likely not running because the motor is toast, the relay is bad or the signal is out? I'm pretty much ruling out the controller signal because the furnace thought the blower was working...that tells me the signal is there (maybe??). Maybe a relay? I'm thinking more towards the motor because it had some vibration for a bit (months) and the motor vents are clogged with stuff. What is the common thing to go? Any advice on troubleshooting? I'd rather not get the wires hot to test stuff but have a multimeter of necessary. Oh, and would it be the capacitor? What's common to go out on these?

So what's up?

Thanks in advance!

 

[m8magicandmystery]

possibly heat exchanger sensor...should kick blower on as soon as up to temp from fire chamber..but as well an overlimit/heat switch should shut gas fire if heat exchanger sensor failure..

 

[jim]

It the heat exchanger sensor right at the base of the flame throwers (not technical term I'm sure)? I just cleaned that cause the gas would shut off when that sensor would not read the flame.

So, are you saying that the sensor did shut off the flame but didn't tell the blower to go on? Is it a discrete sensor?

Is there a good way to test the motor and capacitor? They are separate on this unit. I could fire up the power but seems it'll be tough to get it to work if I'm not firing up the flame thrower.

Thanks for the input.

 

[rp7x]

bad blower

take it out and run it on you work bench

 

[Ak nitro]

The fan is seperate of the gas valve assembly, it can run either by a time delay relay or switch in the heat exchanger. The gas valve is interupted by the the high limit switch also located in the heat exchanger, so your house most likely would not have burned down, I have seen several oil fired units cycle completly off the high limit switch because homeowners had stuff blocking the air ducts. I would check how the fan spins, the motor should turn easily, and there should be no noise from the bearings, jumper the fan switch or the time delay relay, see if runs then, if not is the motor getting hot, motors will get really hot and cylce on their thermal protection if they can not start any more. You can check the capacitor with a multimeter that has an ohmeter or most good multimeters have capacitor test options, it would possibly be bulged or deformed if it was bad. It sounds to me like the motor would be the culprit though, if it had been making noise and all of a sudden just stopped, the motor may be shot. Residential motors are cheap and not worth rebuilding. 15 years is long time, If the switch is sending power to the motor I would just replace the motor/cap combo.

 

[jim]

Awesome AK...thanks for the input. I'll check that stuff...thanks for telling me how to do it...there's a reason I'm a mechanical engineer. Will let you know the status...friend has a cheap line on motors so this could be a cheap one. Thanks - Jim

 

[idpwdagrl]

Um...have you cleared the laundry and dog toys from in front of the furnace area? Just a thought...