duct fan (help needed)

Nov 17, 2014
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hello all

first time poster, long time lurker.

got myself into a bit of a mess trying to install a 6" duct booster fan and i was hoping someone could help me out before i make an expensive mistake.

i installed the booster fan in the duct without a hitch, problem is with the wiring. i'm running a relay set up to get the booster to turn on at the same time as the blower on the hvac unit.

this is what i have done: 120V line to the fan. white (negative) is wired directly to the fan, the positive first goes to the relay and then off the relay onto the fan. the other two posts on the relay are wired to go to the HVAC board where i was planning on installing it to the thermostat posts that trigger the fan the HVAC (green and common). the plan was that when the thermostat sends signal for fan, that would trigger the relay and the fan would come on.

that was teh plan because it's not working. any ideas on what i did wrong/how i can do this right? thanks


Apr 2, 2015
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The Green does not become hot with 24 VAC when the inside fan comes on ?

Normally , in heat mode , the fan is brought on by temperature rise of the heat ex-changer . During cool mode , the tstat should activate the Green with 24 VAC .

What kind of tstat do you have ? If it is electronic , you may need to change the programming .

Does the fan come on , when you switch the tstat fan switch from auto to on ?

God bless

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