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Outside A/C unit turns ON when Fan is switched to ON position. This is a problem because when the thermostat calls for heat it turns ON the Fan which also turns on the A/C unit.

The A/C unit is not a heat pump.

The System consists of a Honeywell 9000 Wifi thromostat, Traine XL1200 A/C unit, and Aprilaire 500 Humidifier. All the wires are connected to like colors except the A/C unit which has a red and white wire from the outside unit connected to Yellow and White in the junction box where all the thermostat wires are connected together. I checked the panel on the air handler, thermostat and humidifier and wires are connected as follows:

Red wire connects to R and Rc

Blue wire connects C

Yellow wire connects to Y

White wire connects to W

Green wire connects to G

The humidifier has 2 more wires connected to the solenoid valve and a jumper from R to H to tap the 24v supply from the air handler.

Where or how do I start to trouble shoot for a short?

  • Much better. What makes you think there's a short? – isherwood Feb 21 '18 at 15:20
  • Because I just found it. You asked me write up more info so I did and it doesn't look correct. According to the Aprilaire 500 installation guide the Green wire should go from the thermostat to the G on the Humidifier. Then from the humidifier - Gi output to G on the Furnace. This facilitates the "Test" feature for the humidifier and also allows the humidifier to run in Fan "ON" and Fan "Circulate" modes. THANK YOU for calling me out on my admittedly vague description of the problem. – Dave Esposito Feb 21 '18 at 15:35
  • So you have a solution? Good deal. (That's more of a jumper than a short.). Please provide and accept an answer below for reputation credit, or delete your post. Unresolved questions are ugly. :) – isherwood Feb 21 '18 at 15:43
  • Did this just start happening? If so, what changed? Have you verified that the A/C unit comes on when the thermostat calls for heat, or are you speculating? Most thermostats do not energize G when calling for heat, so this might not be an issue. – Tester101 Feb 22 '18 at 1:43
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The problem is that "all G wires are connected together"

According to the Aprilaire 500 installation guide the Green wire should go from the thermostat to the G on the Humidifier.

Then from the Humidifier Gi output to G on the Furnace.

This facilitates the "Test" feature for the humidifier which turns the Fan on during the test and also allows the Humidifier to run in Fan "ON" and Fan "Circulate" modes.

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