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I have an Amana AMV90704CXBB furnace, and regular programmable thermostat. I took the furnace apart because I have to wash the blower motor wheel. It was covered in construction dust.

In order to take the blower motor out I had to disconnect all the low voltage wires, that goes into main control board on furnace. Unfortunately for me, I was stupid enough and didn’t take any pictures of original wiring.

When I put everything back together and flipped the power switch on side of the furnace-blower motor starts working immediately. Even when thermostat was set on “off”. Now I have a continuously running fan., that won’t shut off.

If I turn furnace to a heat-heater works, thermostat works and after temperature was raises to a settings point-the burners will shout off, as suppose to, but fan won’t stop. If I switch to AC-the thermostat will click, but AC unit outside won’t do anything.

If I disconnect three low voltage wires that goes into a main control board from outside AC unit the heater will work as suppose to. The blower motor/fan will be off. If temps are dropped or you rise the thermostat settings-it will works as it suppose to.

If I switch to cold and lower the temperature on thermostat-it will click, fan motor in furnace will start working, but AC ,since it was disconnected obviously wont work. There is a three wires going into outside AC unit. I’m 99% sure that the green and red(see the pictures) are where they are before I took the unit apart. However-I’m not o sure about white colored wire. I’m sure that thermostat wiring is fine.

Can anyone help me diagnose this problem? What could it be and where this white wire should be on main control board? On the picture-three wires from left wire are going into AC unit. 4 wires from the right one-goes into thermostat. Any help will be greatly appreciated! Thank you so much and please forgive me for my English. Obviously it’s not my native language. Thanks!

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  • Thanks isherwood for editing my question, specially the header, but it's not what i'm asking. i believe that the thermostat wiring is correct,but i'm not sure about white wire that goes into AC unit outside.Thanks! – KShop Oct 17 '18 at 21:04
  • How are the thermostat wires hooked up at the thermostat and outdoor-unit ends of their runs? – ThreePhaseEel Oct 17 '18 at 22:43
  • Thanks for respond ThreePhaseEel! I'll post the pictures tomorrow,because it's too dark outside. – KShop Oct 17 '18 at 23:07
  • Check for a blown 3-amp fuse on the circuit board of the air handler. This thing blows if you mess up the wiring and cross some wires while powered. – raterus Oct 18 '18 at 4:39
  • i think if the fuse was bad-nothing would work. The main control board won't power up and there is probably will be some code light blinking? As I said above- when those three wires, that goes to outside AC unit are disconnected from the board-everything works fine, except for outside AC unit, which won’t power up because it was disconnected. When AC unit wired as it was on first pic-blower fan is continuously running, after I turn on power switch on side of the furnace. Fan is running and it won’t shut off. Furnace is working. But outside AC unit won’t start, when set on cold pics: – KShop Oct 18 '18 at 15:20
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Move the green wire to the outdoor unit from the G terminal to the B/C terminal.

In the wiring diagram for your outdoor unit, the green wire from that unit is connected to the blue wire going into the outdoor unit wiring, which connects to the C terminal on the "comfort alert" (compressor monitor) module. Connecting that green wire to the G terminal connects the circuitry in the "comfort alert" module in series with the input circuit for the control board's G terminal, which means that the current that powers the module is flowing into the G terminal, turning the input on and causing the control board to run the fan all the time.

The fix is easy: moving the green wire to the outdoor unit to the B/C terminal on the control board causes that current to flow back to the other side of the transformer instead of taking a detour through the G terminal input circuit, and will restore the normal blower functionality of your system.

  • Thanks ThreePhaseEel for detailed explanation! – KShop Oct 19 '18 at 15:34
  • @KShop -- we thank people around here by upvoting and/or accepting their answers :) – ThreePhaseEel Oct 19 '18 at 22:22

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