4

I have installed a new a/c with thermostat...easy enough, but thought to add a fan to the mix. Basically, I'd like to add a fan to increase ventilation into a second room that would turn on whenever the A/C turns on. I know you can run to multiple low voltage devices off a single thermostat, but what would be required to add a 110 fan so that it turns on exactly when the A/C turns on?

Thanks, Pradhan

  • 2
    Is that air conditioner of the commodity in-the-window variety? Or is it part of a central system? – wallyk Aug 31 '16 at 4:20
7

All you'd need is a relay. You'll need one with a coil rated for 24VAC (or whatever the thermostat voltage is), and a contact rated to handle the current draw of the fan at line voltage.

  • Connect the ungrounded (hot) feed to the Common terminal of the relay.
  • Connect the ungrounded (hot) wire for the fan, to the Normally Open (NO) terminal of the relay.
  • Connect the grounded (neutral) from the feed, to the grounded (neutral) of the fan.
  • Connect all grounding conductors.
  • Connect a wire from the G terminal on the thermostat, to one of the coil contacts on the relay.
  • Connect a wire from the C (common) terminal of the A/C transformer.

When the thermostat calls for COOL, it should turn on the fan as well.

enter image description here
Didn't add it to the diagram, but it's probably a good idea to have a fuse on the R wire.

  • Any chance you could include a diagram of this? :) – DarthCaniac Aug 31 '16 at 0:14
  • Thanks for your prompt reply. I've seen the RIB2401B relay mentioned. Will that do the trick for the relay? – user2082331 Aug 31 '16 at 0:42
  • 1
    @DarthCaniac How's that? – Tester101 Aug 31 '16 at 1:11
  • 1
    @DarthCaniac any time the thermostat energizes the G terminal. Which is usually if you turn the fan switch to ON, or during a call for COOL. If you wanted it to work for heat too, you'd need to work in the W terminal somehow as well. – Tester101 Aug 31 '16 at 10:11
  • 1
    @ Tester someone needs to get you a copy of InkScape :-) – Carl Witthoft Aug 31 '16 at 14:41
0

The relay will work great, your other option is to use one of these https://www.amazon.com/BCTINT-10031-010-Automated-Vacuum-Switch/dp/B0035YGLZG

They are used to turn on a vacuum when a tool starts running, most of them also have a delay built in so the vacuum would run for a few seconds after the tool shuts off.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.