OT - Follow Up to Oil Furnace Troubleshooting

At least it is still relatively warm...

Couldn't find my VOM yesterday so went in to town for some errands and picked up the cheapest meter I could find. Followed power to the terminal for the fan after church this morning. Have power going to the fan and fan spins freely. Carefully reached in and gave it a spin while it had power and the fan accelerates, but very slowly and never gets up to full speed. Burner cycles on, but I think it is cutting out on the high temp switch due to the lack of airflow resulting in higher supply air temp.

Anyway is a start capacitor going to remedy this or am I looking at a full motor replacement? Either is kind of a bear to reach, but at least I can see the capacitor mounted on the fan housing. Looks like I would need to actually pull the fan out to get at the motor. It is a direct drive fan with the motor mounted inside the fan scroll.

Thanks for the previous responses. Going to be colder tomorrow, need to decide if I am going to call a service guy or not. If it seems like the capacitor will do it I would probably do that myself. I'm cheap enough that I would do the motor too, but tomorrow is a work day and I'm not sure I can take the time to do it. Wish the supply houses would have been open this weekend, but with the holiday there hasn't been a way to get parts since Thursday.

Kirk

Yeah that does sound like the start capacitor is bad. I don't suppose your cheap meter has a capacitor checker on it, does it?

Did you check what the resistance of the motor windings is? And also, resistance from the windings to ground?

Are you sure it is a start cap & not a run cap????

Either way you need to remove it, test it, replace with a like device.

If the cheap meter is an analog with a 1k ohm meter setting on it then he can use it to test a cap. With the cap unhooked and discharged, touch the leads to the terminals. The needle should go up and then come down more slowly. The larger the capacitor the slower the needle will come down. After it has done this swap leads to terminals and observe the effects. There is a learning curve to this but it is possible.

Hi, do you have a rewind shop or even ac repair guy near you? You could take motor to him to test repair and you put it back in place. Save some bread that way. Ed will

induction split phase motors usually only fail in the bearings and capacitor. If it turns, it is probably the cap. Jim

The fan/motor assembly should slide out easily, usually a couple screws hold it in place. Sounds like the run cap is bad, but try to move the motor shaft side to side. If any side play the bearings are bad and the motor will need to be replaced. End play is acceptable.

If the cap is bad, get the Mfd number and voltage off the old one. The Mfd must be the same, the voltage same or higher.

If the motor is bad, you'll need to get the entire housing out so it can be worked on. Usually the motor will have to come out while the fan stays in the housing. Be easy with the fan, use penetrant and don't bend it! It can be tricky to remount the motor, especially if it is a band type mount. Just take your time, get everything centered and be sure nothing is rubbing.

Steve, I like to fix my own stuff, and have repaired motors and such, but I have never known how to properly check a capacitor. How is it done?

Ross

Kirk Grau,
Furnaces only break when it's a holiday, late at night, weekend, or the coldest day. If I were you I would have all the spare parts you will ever need to repair it, including another fan motor. If you have never oiled the fan motor, it's a good chance a bushing may be worn out, rotor rubbing on stator. Only know when you take motor apart. It will have similar symptoms as a bad run capacitor.

Where I live, it's hard to find any HVAC to work on oil.

So I had a stock pile of spare parts, pumps, nozzles, filters, transformers, temperature sensors, fan switches, thermostats, spark rods, induction motors, fan motors.

I hated smelling like oil every time I worked on them. So I got rid of all my oil furnaces decades ago.
george

The ovens I work on and the blowers we have for EVAC are the same to what you have. It is the Cap. Either 7.5 or 10 Mfd. I would put the little bigger one on cause it lets the motor start a little easier. That is how we test the blowers with a little spin and then give her the juice. The only other thing would be the start winding. After you change the cap she should spin right up. If it is still a slow spin up you need a new motor. Any guy who works on furnaces could sell you a used one cheap. Is it inside the blower or and external belt drive? Most are in the 1/3 horse power range. I posted a few pictures of the ones I build up for portable use a couple of months ago.

OK, guess I am looking at a new motor. Supply house opened this morning and I picked up a new capacitor. Plugged it in and hit the juice before buttoning it back up. Burner starts, hear relay for fan after a minute or so, fan never moves. Reach in (carefully) and give the fan a spin and it starts up and now gets up to speed. Guess I needed the cap since now it runs enough to move some air, but still looking at a new motor. Looks like a real bugger to get out. I am not seeing anything that looks like it slides the assembly for removal.

Might call the service guy now since I don't want to contort myself to reach it and don't own any trained monkeys with tiny to reach things like this.

Appreciate the help so far on this.

After you see how easy it is to pull fan out. And replace motor, you will do it next time. Make sure you Make a way to oil motor with out removing it from furnace.

Motor probably had a switch inside that cuts out the starting winding.
I'd try cleaning the points on the switch.