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Old 04-30-2018, 11:08 AM   #1
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Question Reversing a Fantastic fan ?

Hi everyone,

We had a fantastic fan and a regular vent in our 2006 25' FB Safari. Last year we had a 2nd fantastic fan installed in the front bed room. Much to our disappointment that 2nd fan only exhausted. The wife and I both though we asked for a model that reversed so we could get flow through without opening any of the coach windows.

Anyway, I thought it would be a simple enough process to install a DPDT switch to simply reverse the polarity to the fan motor getting it to reverse. Well, long story short (no pun intended), I had a devil of a time making it work. I could get the fan to work in the proper direction, but when I went to reverse the polarity, the 4 amp fuse in the fan would blow (indicating a short). This was how I wired the reverse switch.



Anyone have any ideas on why I couldn't make this work?

Thank,
L
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Old 04-30-2018, 11:16 AM   #2
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Your wiring diagram looks spot on. If there are no other components on the motor leads, it should work fine. Is this a switch that is "center off" or just one position or the other? That could be part of the problem.

If you have the motor running in one direction, and flip the reversing switch to the opposite direction before the motor completely stops turning, you will probably quickly blow the fuse because of the amount of current the motor will draw when trying to reverse from running in the other direction. It's at least double the running current... That current can be very high, to put it mildly...

Did you try waiting for the fan to stop completely before reversing direction?
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Old 04-30-2018, 11:18 AM   #3
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rmkrum beat me to it.

The switch should have a center off position. Throw the switch to the off position and let the fan stop before changing it to the opposite direction. If the motor is turning when the voltage is reversed, it will draw a surge of current and blow the fuse.

Al
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Old 04-30-2018, 11:21 AM   #4
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It could be several reasons.
1) If it is a simple DC armature motor, they may have put a diode across the motor terminals allowing one way hookup, that would blow a fuse with reversed power applied.
2) If it is some other type of motor with a driver board, the driver board is typically only wired for one polarity. That will blow a fuse.
3) There may be some other hidden wiring between your switch & motor circuit.

If it blows a fuse, I would not make any attempts to "try again" until you have it all figured out. You could damage something.
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Old 04-30-2018, 01:48 PM   #5
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Thanks for the rapid reply folks.

Quote:
Originally Posted by rmkrum View Post
Your wiring diagram looks spot on. If there are no other components on the motor leads, it should work fine. Is this a switch that is "center off" or just one position or the other? That could be part of the problem....

Did you try waiting for the fan to stop completely before reversing direction?

Quote:
Originally Posted by Al and Missy View Post
The switch should have a center off position. Throw the switch to the off position and let the fan stop before changing it to the opposite direction. If the motor is turning when the voltage is reversed, it will draw a surge of current and blow the fuse.
To address the two issues:

1) Yes the switch has a center off position, so I'm good on that.

2) As for having the motor stop completely, before reversing power, I know I did it while it was still turning the first time I tried it. POP! And I'm sure I tried it from a stop as well with the same results which leads us to Wayne's reply...

Quote:
Originally Posted by WayneG View Post
2) If it is some other type of motor with a driver board, the driver board is typically only wired for one polarity. That will blow a fuse.
I think this may be the issue. There was a circuit board for the thermostat and I'm sure other stuff on there too. Which takes up to Wayne's next statement....

Quote:
Originally Posted by WayneG View Post
If it blows a fuse, I would not make any attempts to "try again" until you have it all figured out. You could damage something.
That's why I consulted the experts here! I figured someone here had tried this once upon a time...

Worst case I'm out the $8 or $9 on the switch and $4-5 on fuses...
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Old 04-30-2018, 01:54 PM   #6
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I contacted Fantastic Fan and they sent me the wiring diagrams for my fans. Give that a shot. BTW, my fans both have the electric open and close with the rain sensor, and one has a thermostat. The reversing switch is wired in series with the motor. If you have yours wired to the input of the fan, move it to the motor leads.

Al
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Old 04-30-2018, 02:41 PM   #7
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you need a Double pole double throw 3 position switch.
https://www.delcity.net/store/Flat-T...gaAl4ZEALw_wcB

it has three position with center being OFF.. did it on my 2005 and it really make a nice difference. you can do it on fan with rocker switch and not with the thermostat on the wall type.

they are referred to as "on off on"
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Old 05-01-2018, 10:55 AM   #8
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By the way, those fans are designed to blow out, and out only, for a reason.

This way, you avoid the risk of drawing in sewer gas that vents out the roof from the black tank below.

It may even be required under the RV building code (or whatever might be the correct term).
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Old 05-01-2018, 11:43 AM   #9
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Decided to reverse the rear fantastic fan on my 2017 FC25FB today to improve air flow. The wires that must be reversed on my Airstream are a red one from the fan speed setting and a white one from the on/off switch that each go to the fan motor. You can actually see the wires that must be reversed before you even start by looking up at the fan from inside the Airstream. I just removed the two interior housings, added a one foot section to each wire, and flip-flopped where they were plugged in. (In other words, I connected the white wire to where the red wire was plugged in and connected the red wire to where the white wire was plugged in.) Now my rear fan draws air in and my front fan exhausts it out. If you add a dpdt switch between these same two wires, you will then be able to switch from intake to exhaust.

The key to all of this is that you want to reverse, or dpdt switch, the red and white wires that you can see above the fan motor.
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Old 05-01-2018, 12:05 PM   #10
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Quote:
Originally Posted by carl2591 View Post
you need a Double pole double throw 3 position switch.
https://www.delcity.net/store/Flat-T...gaAl4ZEALw_wcB

it has three position with center being OFF.. did it on my 2005 and it really make a nice difference. you can do it on fan with rocker switch and not with the thermostat on the wall type.

they are referred to as "on off on"
My thermostat on the wall fan has an IN/OFF/OUT switch from the factory. The wiring diagram shows the standard reversing ON-OFF-ON switch wired in the feed to the motor.

Al
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Old 05-01-2018, 02:27 PM   #11
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Both of my fans have in/off/out switches. On one, I installed a free kit Fantastic Fan sent me.
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Old 05-01-2018, 10:50 PM   #12
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Quote:
Originally Posted by Al and Missy View Post
I contacted Fantastic Fan and they sent me the wiring diagrams for my fans.
When I contacted them, they sent me both the wiring diagrams and the in/out switches for free. I was happy and impressed, right up until I started re-wiring the units...

It took a long time, and was marginally worth the effort. Most of the time, I open a window and use the fan to vent outward.

Glenn
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Old 05-02-2018, 11:58 AM   #13
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Thanks everyone. I just shot the fantastic fan folks an e-mail inquiry.

Lonnie
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Old 05-02-2018, 02:00 PM   #14
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See the red and white wires going into the fan motor in the first large picture of the fantastic fan? http://www.loveyourrv.com/installing...c-vent-fan-rv/

I believe those are the wires that you need to connect to your DPDT switch. These are the two wires that I reversed to make my fan go backwards. Your DPDT switch just toggles these two wires between straight through and crisscrossed to make the fan go out or in.
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