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Thread: Greenhouse ventilation motors, thermostat, and wiring

  1. #1
    DIY Senior Member TJanak's Avatar
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    Default Greenhouse ventilation motors, thermostat, and wiring

    I rent space in a greenhouse that has two ventilation fans, 1 HP motors each wired for 240V. This year one motor was bad so it was partially disconnected (one leg) and the other was turning at a much slower speed and I only got 68V across both legs at this motor. These motors are controlled by a Dayton line voltage thermostat.

    Opening up the fusebox, I could not figure out the wiring. Looked like they were wired in series with the thermostat stuck in there somewhere. I took it all apart and started over, with two legs from the fuses going to the thermostat and then on to only one fan. It now runs correctly.

    Problem is I would like to hook up the other fan but the thermostat is rated 8 amps at 240V. These motors are each ~6 amps. I know both fans used to run correctly (simultaneously) several years ago. Were they simply running 12 amps through the thermostat or could they be hooked up in a way that the thermostat could control both fans without full current going through the thermostat?

    I don't see how but figured I would ask.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    You could use the thermostat to control a power contactor...just make sure the contactor contact rating is sufficient for the motors being used. The coil of that should easily be within the range of the thermostat's ability.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY Senior Member dlarrivee's Avatar
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    It would probably be just as cheap to buy a second line voltage thermostat...

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    DIY Senior Member TJanak's Avatar
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    I guess they must have both been run through the thermostat, even though it would be overloaded. Two thermostats would work but it would be better if both fans turned on and off at the same time. Thanks.

  5. #5
    Moderator & Master Plumber hj's Avatar
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    The description is confusing. IF the motor was bad and one leg was disconnected, why would you now try to resurrect it? A 240v thermostat should have had 4 terminals, but you imply it only had one line going through it. What was connected in series? The motors? If so, disconnecting the wire from one of them should also have also kept the other one from working until it was rewired.

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