The heater fan at my house has stopped working. It made a lot of noise when starting, and eventually had to be rotated by hand for it to start. Based on this, I think the motor start capacitor may be faulty. It’s rated for 7 mF, 370 VAC. Will any capacitor with the same capacity and voltage rating be a suitable replacement?
Yes. If you have access to Grainger, they probably have one in stock. Otherwise check the yellow pages under Electric Motors.
7 uF is on the small side for a starting capacitor, though. Are you sure it is not a run capacitor? If it has a plastic case it is probably a starting capacitor, if metal it is likely a run capacitor. Run capacitors have are made to operate with a 100% duty cycle. Starting capacitors will overheat in a few seconds. A starting capacitor used as a run capacitor will have a lifetime measured in minutes. If you are unsure, take the cap to a motor shop and they will supply an appropriate replacement.
It has a metal case, fastened to the outside of the fan housing. I’ll look deeper inside the motor.
Some additional research has indicated that the motor may be a permanent split capacitor type, and such a motor does not have a separate start capacitor. The furnace is a Lennox G16, with a direct drive blower. Am I still correct in looking for a replacement run capacitor?
The metal vs. plastic deal is often true but isn’t necessarily true. We sell plenty of motors that use plastic body run capacitors. However, it’s probably best to use a replacement that is as close to the original as possible. Run vs start is in the wiring of the motor so you can ask any supply house for an oil filled 7-370 and you’ll be fine, assuming the capacitor is the problem.
If you live in a metropolitan area, you can take the motor to a “motor rewind” shop and they can check it out for you, often while you wait. They should also have the capacitor you need in stock.
Grainger will only sell to wholesale accounts, so that may not work. Other folks in the Philly market who might sell to you are Johnstone Supply, United Refrigeration, R E Michel, or Sid Harvey.
It might not necessarly be the capacitor.
I fixed an air conditioner fan that had to be started by hand in just the way you described. I got the fan out of the AC took the motor apart and gave all parts a thorough cleaning. (Yeah, it was messy in there.) Also I oiled the bearings, put everything back together and it has worked fine ever since. Just thought you might want to try this solution as opposed to searching for just the right capacitor.
Well, I found a replacement capacitor, but it still doesn’t work. Unfortunately, the next step I would try is wolf_meister’s suggestion, but it looks like major disassembly is required to get the fan out of the heater. At least I was able to restart the motor. Whether the new capacitor helped in that regard is unknown, but we should be able to get by until the new heating system gets installed in a day or so.
Having recently been through this with my Lennox forced air furnace:
Hopefully the entire blower will come out as a unit. Mine didn’t look like it would until a lot of inspection revealed that two painlessly accessed screws allowed it to come out fairly simply…way less work than I was expecting.
Look for a manufacturers web site. Odds are that you can get an exact fit replacement part.
Lastly, if the new motor has oiling ports, install some pvc tubing so you can oil it insitu.
No, I found that removing the blower requires disassembling the rest of the heater to get it out.
I can see the fan move slightly, and I can feel where the stator field wants to lock the rotor in place when I try to assist it. As far as I can tell, either the main or auxiliary coil has shorted out or otherwise been rendered ineffective.
The entire system is going to be replaced in a day or so. I’m giving up for now, though I’ll probably autopsy the motor once the heater is taken out.
On the upside, I now have two capacitors to play around with.