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I'm trying to install a wireless thermostat but i ran into issue putting in an external thermostat. I have a 2 Stage Cool / 1 Stage heat system.

I have the Red 24V from Air Handler connected to R. I have a external 24 Volt Transformer Hooked up to Rc, and C. I get 27 volts between Rc, and C. However when i tell thermostat to turn on fan nothing happens. If i remove external transformer and jump Rc, and R using AHU transformer everything works fine.

What could be causing this?

Photo of Wiring

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  • The external transformer probably doesn't have enough power to pull the relay. What is the Volt-Ampere (VA) rating of the transformer? – Tester101 Sep 4 '14 at 23:36
  • Actually, now that I think about it. When you say "external transfirmer", you probably mean something like a wall wart. In that case, it will have an ampere rating not Volt-Ampere. – Tester101 Sep 4 '14 at 23:43
  • Output: AC 24V 300mA. galleryplus.ebayimg.com/ws/web/261115137424_1_0_1/1000x1000.jpg – Brian Weaver Sep 4 '14 at 23:47
  • Any idea what the relay is rated? Or could you include the make and model of the air handler? – Tester101 Sep 4 '14 at 23:52
  • Not home right now to get specifics. But its a Rheem 3 Ton 16 Seer. Im just worried its something complex cause i have a $150 thermostat coming tomorrow. – Brian Weaver Sep 4 '14 at 23:52

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