Electric hook-up; Attic fan

[timbirr]

Any electric gurus? Just had a new roof put on. The roofers said the vent that housed my thermostatically-controlled attic fan was about shot and should be replaced -- it was only 37 years old.

So, ended up with a whole new unit. Of course, it was up to me to rewire the beast.

From the house is a romex cable with black, red, white and green 12 AWG.

The old fan was hooked up black to thermostat. White to White and green to box ground clip, with the red wire taped over inside the box.

I hooked up new fan basically the same way, except I put a wirenut (scotch lock) on the red wire and wrapped it up with electrical tape.

It has been fairly cool with outside temps hitting 70, so with the fan thermo at 90, it hasn't kicked on. I did spend about 5-10 minutes after the install with the thermo dialed down to 60 degrees, but the fan didn't kick-on then, but I had to dash, so dialed it back up to 90 before departing the attic.

Maybe I am being a bit paranoid, but I am thinking it's not working.....Would it be OK to bypass the thermostat -- that is just hook the hot black lead directly into the fan to see if it works. I'm pretty untalented in electrical works, but seems to me the thermostat is just a fancy on/off switch right?

Or, am I just too anxious.....was my five minute trial at the 60- degree setting enough that it should have kicked on?

[dpb]

[e-mail] wrote: ...

Sounds right --

That sounds good, too...assuming it's a 120V motor, not 240V, which would also be the normal...

Sure, and yes, respectively...

Should have kicked on very soon after you turned in on -- would be highly unusual to have a time delay on a thermostat there.

Questions --

1. Are you sure the breaker to the thermostat is on? Maybe either it was turned off to service or when the roofers disconnected the fan they could have shorted the leads and tripped the breaker...

1. You should be able to hear the relay contacts of the thermostat open/close as you turn the setting up/down past the current temperature.

If you have a VOM, you can test whether the contacts are closing or not or simply use a light bulb type tester to check for power.

I'm guessing probably it's the breaker is off/tripped...

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[RBM]

Sounds like you have it right. Those cheesy through the roof attic ventilators don't kick on until it's pretty hot, so running the stat up and down may not work. You can test it by connecting the hot leg to the load side of the stat.

[timbirr]

OP here again:

Thanks for the replies:

1). As to the breaker, the roofers never touched them, they just took out the old fan and fastened it to the rafters, never disconnected power. When I did the rewire, I turned off all the breakers for the house, except for the dryer, electric range and well pump, since I had no idea which of the breakers controlled the fan. Then I flipped them back on....of course, in the meantime, the responsible breaker could have failed, but I hate to willy-nilly start replacing them, as I have a "split buss" panel and there is NO main disconnect to the panel, meaning "all hot, all the time."

2) According to the fan manual the roofers left me, the fan is 120.

3) Reacting to the "cheesy thermostat" idea, they did note in the GAF install/owners manual for this new fan that the thermostat was only "approximately" accurate....so I think I'll wait until the weather warms, probably next week and see if it kicks on. If it does, fine. If not, I guess I'll go pull it apart, try the direct connect and work from that result (VOM, continuity tester, etal).

Only problem is I have an 1980's era analog VOM that I still don't really understand how to operate.....

[Joseph Meehan]

Sorry I don't have any direct advice for you, but maybe I can offer a suggestion that may get you thinking about what you really want to do.

Those roof fan vents are more often than not less effective and eat energy, than a properly sized passive vent system. There are situations where it is not possible or practical to use passive venting, but most of the time there is. Since passive vent is cheap to install and no one wants to bother advertising them, all the adds you see are for the active systems.

[dpb]

Certainly no reason to replace any breaker, the only question was to ensure you actually had power _to_ the thermostat...

As expected, but never hurts to be sure...

Yeah, but that's probably "only" 5F or so off of what the the numbers stamped on the case indicate, not 30. If the temperature was 70-80 in the attic and you turned it all the way down, I would certainly expect the contacts to close. If it was way cool in the early morning, then maybe...

...

Set it on the AC Voltage measurement and the range greater than 120V --

300V would be a typical choice. Simply measure the voltage across the black and white wires to the thermostat. If there's 120V there, that's step one. Turn the thermostat to lowest temperature setting and do same measurement on the output to neutral. If voltage, all is well at that point. If not, then you've isolated it to either a bad set of contacts (or miswiring as remote chance) or the temperature isn't high enough. Will, of course, have to do the above test at a temperature above the minimum.

It's certainly no problem to connect the fan leads directly to the input to the thermostat to make sure it does operate if you do have power to the thermostat...

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[mm]

One shouldn't be replacing breakers willy-nilly in any case. I don't think it's the breaker, but if it comes to that, you take the cover off the panel and use your VOM to see if any of them are dead, measuring at the screws on the far sides from the midline of the panel. Each screw should be 110. If it's a 220 circuit, it will have two breakers each with 110.

I think they are talking about 1 to 4 degrees, and have that in there so no one will yell at them for that. My fan thermostat doesn't have numbers on it, I think for the same reason. If perchance it does turn out to be far off what it says, you should probably set it for what it should be, regardless of the number it is set to. That is, if it is supposed to go on at 90, it should be set that way, regardless of what number the shaft or knob is pointing at.

There was nothing wrong with 80's VOMs. I have one and I use it, and I have from the 70's, 90's and 00's too. I think I had a small one from the 60's that I was measuring something under the hood with, and then left it there, and when I opened the hood 100 miles later, all that was there was two frayed wires.

But that's ot. Does your meter have a knob? Is setting the knob the problem? Or is knowing which holes to plug in the wires the problem?

You're going to be forever stuck in kindergarten if you don't learn how to use a meter. So please post back.

[mm]

There is another wire already hooked up from the thermostat to the fan motor. It might be black, but who knows.

There should be 110v between the white and black that you noted.**

If the fan isn't running there should be 110v between the two wires of the thermostat. If there is and the thermostat is set all the way down, then it implies the thermostat is broken. You should hear a small click from the stat when turning it up and down, but it won't click at the same setting in both directions.

**If there isn't, you have a problem with power. Breaker is tripped, for example. Is there any chance there is a wall switch somewhere to turn the fan off with. I have one, that I use in the late fall and early spring when I want the heat from the sun to warm the attic and warm my house. I keep the fan turned off all winter too, in case there is a warm day. I don't think it would go on anyhow though.

[timbirr]

OP again.

OK, I posted a separate thread on VOM in case anyone is as clueless as I am about them....in regards to some other suggestions, someone mentioned a "light switch" that might be holding back the current. You know about four feet from me right now, pretty much just below the attic location of the fan, is a light switch on the wall that doesn't seem to control anything. I remember screwing around with it this winter when I was doing some cleaning, and I just looked now and it is switched off. Now, of course, it couldn't be so simple...but you never know....

Once some other family members come home, I'll switch it on, go back into the attic and crank the thermo down again....you never know....I'd do it now, but my ladder is a tad short and the attic is a tad high and I have to stretch from the top step to get into the space, so I prefer someone to hold the ladder when I go up.....

[Terry]

The easiest way to check the thermostat is to just disconnect it (with the breaker off). Wire nut the two wires together. If the fan comes on you know it is the thermostat.

You already said that putting the thermostat in the lowest setting made it come on. That tells you that everything else is working.

[Bob M.]

I have a problem with the tape. In the hot environment of the attic, tape will come un-stuck and unwind from whatever it's wrapped on, fan or no fan. Wire nut it.

Note that wire nut and scotch-lock are not the same thing. A "scotch lock" is an IDC (insulation displacement connector); it slices the insulation and makes contact with the wire. Not much contact at that. I'd feel better with a wire nut or a crimp connection.