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I am trying to upgrade to a programmable thermostat. I bought the Honeywell RTH9580 with WiFi. I can get power to the new thermostat and get the fan running. However, it will not work when the fan is set to automatic, or get the AC or Heat going.

The furnace board has the following wires

  • A jumper from Y to G
  • White wire into W1, with jumper to W2
  • Red wire to R
  • Green wire to G
  • Blue wire to C

I set up the Honeywell as follows:

  • White wire to W1
  • Red wire to Rc with jumper left in place to R
  • Green wire to Y (and also tried G)
  • Blue wire to C

Like I said the fan will run when set to run but not auto and neither AC nor Heat kicks in.

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    Did you look at the instructions pages 8-19, especially pages 16-18? – wallyk May 26 '14 at 18:00
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    How was the old one wired? – Tester101 May 26 '14 at 20:48
  • Put the old thermostat back on and verify it all still works. Should help with your wiring diagram as well. – rjt May 26 '14 at 21:12
  • Tester101, I was able to re-install the old thermostat just fine. It was wired as follows: Green wire to G, White wire to W, Red wire to to Rc (with jumper to R), and Blue wire to Y. – user21743 May 27 '14 at 20:43
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I would remove the jumper from Y to G and use your yellow for Y.

On the thermostat and the furnace you should have Y , yellow (cooling) G, green (fan) R, red (power 24v) jumper R to Rc, Rh W, white (heat) no jumper, on thermostat use W1 (first stage heat). Leave W2 unused and set the thermostat to single stage heat, single stage cool, that way the thermostat knows that there is nothing connected to its W2 terminal. C, blue (common/ground) this wire allows the thermostat to draw power from the HVAC system as opposed to using the batteries.

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In my experience, thermostats must be programmed to operate the type of system you have (and must be wired properly.) For example, there is a setting that tells the thermostat whether you have electric heat or a gas furnace, and so forth. There are more variables than you might think, and if they are set wrong you can get weird behavior like the fan not blowing, or getting A/C instead of heat, etc.

Read the installation instructions carefully. Confirm that your wires are connected in the right order, then follow the programming instructions all the way through.

Of course, you will need to know some technical details about your system, like whether or not it has electric heat backup for example. If you do not know these correct answer to one of the questions during setup, find out before you proceed.

Don't forget that calling Honeywell technical support (listed on the owners manual of your new thermostat) could be a big help. I have called them before and been pleased by their helpfulness.

  • I did call Honeywell support, and after 30+ min of holding they guided me through the process. We ended up with adding a second unused wire to the C terminal on the furnace as well as the thermostat. The support rep was very patient and as many combinations we tried we finally found one that worked. – user21743 May 28 '14 at 21:39
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Your fan (G) is jumpered to the cooling system (Y). You need to wire green to Y on the thermostat and set the thermostat fan control (menu -> system setup) to tell it the heating system is controlling the fan. You'll never be able to run just the fan with this configuration since you don't have a separate line, when the AC turns on, so will the fan. This may not work if your heating system is forced air, check with your HVAC manual to see if this is supported. Another option you may want to consider is the "add-a-wire" devices that convert a 4 wire line into a 5 wire line, then you can remove the jumppered connection on the HVAC and have a dedicated fan connection.

  • I also have an unused yellow wire that was pulled through the wall. Would it be better to reconfigure, or would that cause more issues / deeper understanding of what exactly is going to the furnace control board? – user21743 May 27 '14 at 20:50
  • An unused wire is best. See the chart here, particularly the letters (colors are a convention but don't have to be followed): wiki.xtronics.com/index.php/Thermostat_signals_and_wiring – BMitch May 27 '14 at 21:00

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