I'm trying to wire a two stage exhaust fan for my greenhouse. The motor comes set up for 240v wiring and is to be controlled by a thermostat. I undertsand how to get the 240v from the panel, but can't seem to figure out the thermostat wiring diagram. What connects to what coming from the panel and going to the motor? See photos 1)thermostat wires and housing label, 2) thermostat wiring diagram. The motor has three terminals labeled high, low, and common.

thermostat wires and housing label

thermostat wiring diagram

  • Yup, that's clear as mud. Violet should presumably go to "high" and blue should presumably go to "low", looking at the paper, but the paper and the label don't seem to agree - the label refers to both colors as "cool 2" (and the others as "Heat 1") while the paper refers to first and second stage cooling (and heating). Call or email the vendor. – Ecnerwal Apr 17 '15 at 12:51

That thermostat is not meant to switch high voltage. You need to use a 240V thermostat. Or wire that one to switch a relay to switch the fan.

A 240V t-stat would be easier. It simply wires like a light switch.

To use a relay you need something like this.

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Here is how a furnace controls it's 2 speeds high and low, high is for cooling and fan on. Low is for the heat mode. Note the fan relay has 1 normally open and 1 normally closed switch, the fan relay is controlled by the thermostats Green circuit shown on the thermostat diagram at the left side of the diagram. Cool mode and the fan on speed is high speed fan. High speed is controlled by the normally open switch in the fan relay. Low speed is the heat speed and is controlled by the time or temperature delay on the fan relays normally closed switch. Note the 24 volt coil in the fan relay that gets energized via the thermostats Green circuit, see it says to green on tstat and to 24 v common? The common lead of the 2 speed fan motor is the Common terminal at the top of the blower motor and marked Common. Common in a motor is the point at which the run and start winding's meet, there is no "common" winding just run and start winding's and the speeds are on the run winding as shown.

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