I have this fan installed. Here's the wiring diagram...

enter image description here

The fan has been running fine for about a month and all of a sudden it started acting like it has no power. I checked the voltage at the power source (a receptacle box for the other attic fan), at the switches on the wall and on the fan itself. I see 120v everywhere except at the fan. I only see 71 (low) to 92 (high) there.

I noticed one other really odd thing. When on low, the voltage is correct. When on high, the voltage at the 3-way high/low switch shows as 210V. I'm not sure how that's even possible on a 120V circuit? To get this reading, I'm checking from the neutral to the switch's "high" terminal.

I've checked and re-checked to ensure the wiring matches the diagram. Everything is 14AWG which is what the install instructions called for. And again, this has been working fine until a few days ago.

At this point I'm thinking the romex cable between the high/low switch and the fan might be fried. Never heard of that happening though.

Any ideas what's going on?

UPDATE 1: Adding pics enter image description here enter image description here

Note the extra red is not used on either end.

UDPATE 2: I checked the voltage at the fan again, only this time I disconnected the fan first. Now I'm showing 120V as expected on both high/low wires when the switch is set to them.

Barring any other ideas, I'm thinking the motor is partially burnt out. This would also explain why it worked for a while and then stopped working.

UPDATE 3: Adding fan pics enter image description here enter image description here

Also, it's wicked hot up there, but I read somewhere that this motor is supposed to have some kind of heat protection? Not sure if that's sales mumbo jumbo or not.

I also learned that there is suppose to be a 10 year warrantee on the fan. We'll see how Home Depot handles that because I'm not about to rip the entire thing out of my attic.

UPDATE 4 (PROBLEM RESOLVED): The 3-way (high/low) switch was definitely bad. Replacing it resolve all power issues but the fan still acted like it had low power. The blades were barely spinning.

Ventamatic was willing to honor their 10-year warranty - but after pulling the motor down, I discovered that the hex screw on the belt wheel was loose (see added pic below). This screw was impossible to see or adjust without pulling the motor out into the open. The wheel was tight enough that it didn't fall off when the motor was removed, but it was loose enough that it was slipping on and off when under pressure. Thus the blades were barely moving. enter image description here

SUMMARY: The fan worked great for a while. At some point, the belt wheel became loose and around the same time the 3-way (High/Low) switch started failing. Because both things went wrong at the same time it was difficult to nail down the source of the problem. Hopefully, this update will be helpful to someone else who gets the joy of trouble-shooting one of these fans!

  • Adding a pic of your actual switch wiring may help someone spot something wrong. – FreeMan Jul 22 '20 at 22:37
  • What are the switches rated for? What is the motor rating fla? – Ed Beal Jul 23 '20 at 1:09
  • The switches came with the fan and are rated for 15 amps. I'm fairly certain at this point that the high/low switch is faulty though. If I put any backward pressure on the "high" screw, it stops working. I noticed this when I pushed it into the wall. I'll attach a few images of the fan which show the model/specs. – Mark Jul 23 '20 at 16:18
  • Double check the wiring on your high/low switch. Most three way switches I've seen puts the common screw on one side, and the two switched screws on the other, and if yours follows this convention, it's wired incorrectly. The common screw should be connected to the on/off screw. If this is reversed, then only one of the two settings will work. – Nate S. Jul 23 '20 at 17:18
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    Thanks for the additional ideas y'all. @NateS. It's wired correctly. If you look closely, you can see that the common screw is black on the 3-watch switch and matches the placement in the diagram. – Mark Jul 23 '20 at 23:16

To me it sounds like your switch is failing or arcing and not providing power under load.

Can you spin the fan? It should not be hard to spin Just verify prior to the next step.

General purpose snap switches need to be 2x the motor rating.

Turn the breaker off

I would pull your high & low connections from the switch and insulate 1 take the other directly to the power on the first switch . Turn the breaker on if the fan spins up get motor rated single pole single throw and single pole double throw switches.

The high voltage measured on low when the fan is on high is a “transformer type action “ from the different number of windings in high and low

  • Thanks for the ideas! I tried replacing the high/low switch. Exact same problem. I can spin the fan just fine. No tension really. I tried wiring the "high" circuit directly to the power source line and it still ran slow. I also tried wiring it to a separate house circuit just to see if there was anything else funny going on. Same result. So the "transformer type action" is something you would expect to see on that switch? No cause for concern there? – Mark Jul 22 '20 at 23:16
  • @Mark -- the "transformer type action" is a function of the motor windings, not the switch – ThreePhaseEel Jul 22 '20 at 23:32
  • Ok. I think that makes sense. So 120V is going to the fan and the inactive pole on the 3-way switch is showing the "transformed" voltage? – Mark Jul 22 '20 at 23:51
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    Yes it is actually the windings in close contact transform voltages based on the number of turns so the step up sounds right. – Ed Beal Jul 23 '20 at 1:06
  • This may actually be the correct answer after all. The high/low switch is now acting up. Considering that I changed that switch out and the fan still ran slow, I'm thinking it has to be the motor now. I'm wondering if a failing switch might have caused the motor to burn out? I'm not sure how to validate that other than running it directly to a circuit with no switches (which I've done and it ran slow). – Mark Jul 23 '20 at 16:28

See UPDATE 4 and the added SUMMARY. Everything is running great now!

Thanks again for all the ideas and help y'all! Much appreciated!

  • Please edit the contents of Update 4 and the Summary into your answer, so I can give you a +1 for it :) – ThreePhaseEel Jul 30 '20 at 11:48

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