Attic Fan Runs Slow

kcarrier · 07-24-2009, 09:05 PM

I have replace the motor on our attic fan (like a whole house fan) because the old one started running only on one slow speed. After mounting and wiring in the new one it still runs on only one slow speed. When I've bi-passed the switch it makes no difference. It was a solid-state 2 speed switch. Can anyone help? Wouldn't bi-passing the switch make it run on it's highest speed???

220/221 · 07-24-2009, 09:33 PM

You should have checked the supply voltage befor you replaced the unit.

Low voltage = slow speed. Could be a wiring issue....could be other issues.

Get a voltage tester or call somebody

kcarrier · 07-25-2009, 03:11 PM

Check the voltage and I have 110 coming in like I'm supposed to. Any other ideas???

micromind · 07-25-2009, 04:30 PM

If the motor has two brown (usually) wires going to a capacitor (round or oval thing about 2-3" long), then it's a PSC (Permanent Split Capacitor) type.

A bad capacitor will cause a PSC motor to run slow.

Rob

kcarrier · 07-25-2009, 04:37 PM

I got a brand new capacitor with the new motor. I found an online source that says it is the right size capacitor for that motor. Yes, it does have 2 brown wires running to it. The guy who sold me the motor said either wire could run to either side of the capacitor, but not the same side. Was he right?

KeithM62948 · 07-25-2009, 06:43 PM

Did you perform your voltage check under load?

micromind · 07-25-2009, 10:36 PM

One of the brown wires goes to one side of the capacitor, the other one goes to the other side. AC capacitors are not polarity sensitive, so it doesn't matter which one goes where.

Is this fan direct drive, or belt drive?

As stated above, was the voltage tested with the motor running? And as close to the motor as safely possible? And tested hot to neutral (not hot to ground)?

Considering that two motors behave the same way, the problem is most likely not associated with the motor.

Rob

kcarrier · 07-26-2009, 11:26 AM

Ya, it's been a real mystery. The new motor came with 3 wires (a black, a white, and a red). However, there is only black and white leading to it. The people that sold me the motor said to wire nut the red one and just wire up the black and white like normal. Should the red be wired up somehow too??? I would have NO idea why I would suddenly have low voltage. I didn't check it while the fan was running, so I might try that. A few years ago the fan worked just fine, then one spring it would only run slow. After bi-passing the switch and seeing it still run slow I (and everyone else giving me advice) assumed a winding was bad in the motor. Maybe I just need to call an electrician to figure out what on earth is going on.

By the way, thanks for all the helpful advice everyone has given!!!

J. V. · 07-26-2009, 12:01 PM

Run a temporary power cord up there and see if a new source of power corrects the problem. If you do not have a meter. You never have told us the voltage or anything else about the motor. Did you ever see the nameplate?

micromind · 07-26-2009, 02:19 PM

This is a two-speed motor. White is always the neutral. Black and red are the two speeds. Look on the nameplate, it should state which is high and low.

As stated above, hook it up (temporarily) to a known good source. White to the neutral (the wide slot of a cord or receptacle) and high speed to the hot.

If you don't know which color is high or low, hook one of them up to the hot, and note the speed. Next hook the other one up. It'll be obvious. Be careful, the unused wire will be hot. It must be insulated.

This is a ways out in left field, but check the voltage on the motor. I doubt that this is the problem, but if the new motor is 230 volts and 115 is applied, it'll run a fan at about 30% of normal speed.

Rob

kcarrier · 07-26-2009, 03:33 PM

I will have to completely dismantle the mounting to see the wiring diagram plate again. I can do that, though. I think the problem is one of two things (or both). I suspicious the red wire is "high". Without that hooked up all I run on is low speed (which actually could be the case). I could also have a switch problem...a solid-state two-speed switch. I will go back and review the literature that came with it. Thanks for the helpful tips!!!!!

AndrewF · 07-26-2009, 09:44 PM

I doubt it is the switch. Switches are generally on/off and have no ability to reduced the voltage.

kcarrier · 07-27-2009, 09:49 AM

I give up. I've called an electrician.

If it's a voltage issue it's over my head anyway.

J. V. · 07-28-2009, 12:25 PM

Quote:

Originally Posted by kcarrier

I give up. I've called an electrician.

If it's a voltage issue it's over my head anyway.

Good call. Everyone cannot be an electrician.

To bad you could not follow the simple steps we provided. I know you could have fixed your problem. I would have put money on it.

kcarrier · 07-28-2009, 01:27 PM

I could be sick!!! The main problem was that the belt was too loose. I know it needed some slack, but I guess where it was allowed too much. The electrician did rewire it to the switch like it was supposed to be...but that really stinks!!!