Need House Thermostat To Trigger 120V Outlet

Hi.
(Long post, sorry)

Here’s the situation:
I (wife) have a whole-house air freshener (“scent machine”) that can pump aroma directly into HVAC, to make the entire house “smell pretty”.

If you hook directly into a/c ductwork, you can’t have it run when the a/c is off, only while a/c fan is running. Fragrance oil will pool up inside the plenum (?) and start to grow bacteria, etc.

So I have two choices and I want choice number #2.

1) run the a/c fan constantly, and let the machine cycle on/off throughout the day as it does by default. Easy, but costly on the electric bill plus wear/tear on air handler.
2) rig a 120v receptacle to be “tripped” or energized only when the a/c fan turns on and off. The unit will still cycle on off, but only when only the a/c fan is running. Hard, but so much better.

I figure the thermostat is 24v (?) so a 24v to 120v relay connected where thermostat connects to air handler.   Then run a simple pigtail female plug or receptacle mounted inside HVAC closet; 120v power would come from another receptacle in the adjoining bedroom.

Relay? “Contactor”?

Here’s what a local electrician told me along with his estimate of $400-$450!

“there are multiple types of relays to accomplish this, depending upon the load the relay has to handle. Being I do not know the load created by this machine you wish to operation, I would do it with a contactor, verse a relay, so it does not stand a chance to be overloaded.“

The scent machine only pulls 14w, so I don’t think there’s an overload concern.

Any words of advice??

Thanks.
// Radar //

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RadarContact

I don't have specifics on your unit, but if it were me, I would tap into the feed for the fan itself, not the thermostat. When the fan gets power, a separate contactor can energize and allow your scent machine to operate.

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My ex once told me I have a perfect face for radio.

I’ll have to research contactors, I’m not familiar. But that’s an interesting approach… need to pull the HVAC schematics and take a look!

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RadarContact

The thermostat connects to a board inside the unit but it doesn't determine when the fan is running. That's why you're best bet is to use the motor hot lead to control a contactor.

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My ex once told me I have a perfect face for radio.

Understood. Great point.

I researched contactors and that seems like overkill as the unit only draws 14w total. So, I will try to figure out which relay to use based on that info.
(From www.engineerfix.com: “ The load capacity of relays is mostly used for applications that carry 10A or less. Any applications that use 10A or more normally use contactors.”

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RadarContact

Yeah, it's definitely overkill. You could use a solid state relay to do the same thing.

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My ex once told me I have a perfect face for radio.

Sweet. I’ll try to find one and then I’ll come back for a thumbs-up! Lol!

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RadarContact