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My A/C doesn't come on when I set the temperature on the Braeburn thermostat very low. Also, the recirculation fan doesn't come on when I set the thermostats fan setting to 'on', as though the indoor unit is not receiving any signal from the thermostat for either cooling or recirculation.

The setup:

  • The AC worked at the end of the summer when we stopped using it.
  • During the cooler months last year I was crawling around the attic doing work up there (I'm fairly fastidious and careful and I didn't bump anything that I'm aware of).
  • I recently had new siding put on my house and the workers let the junction unit next to the outside condenser dangle while they installed the new siding
  • I checked everything after the siding work was done (outside lights, AC, etc) and found the AC unit didn't come on
  • I've measured 250V on the condenser side of the large fuse in the junction box that was left dangling. So, I don't think the workers did anything but am mentioning it here in case I've overlooked something.
  • I've gone up to the attic where the indoor/fan unit is located and noted the wire connectors between like colored wires (red, yellow, green) are still there and weren't accidentally disconnected. See pictures below.
  • Like colored wires between indoor fan unit and outdoor condenser are still firmly connected as well (red, yellow, brown).
  • I've taken pictures of the wiring diagram on the side of the fan unit in the attic which shows RD, BR, GR/BK, WH/BK, WH/BL, YL going to thermostat (optionally, WH/BK and WH/BL tied together. So 5 or 6 wires to thermostat (this is only AC not heat if that matters). See pictures below.
  • I've gone to the thermostat, disconnected the face unit from the wall and measured 27-27.5 volts White and all the other wires (Red, Yellow, Green). The thermostat is a Braeburn. See picture below.

While in the attic I stuck the voltmeter probes into some of the twist-on connectors but didn't measure anything. Before proceeding to take anything apart, what voltage should be across these wires going into the unit:

  1. Red (jumpered to another red running towards condensing unit)
  2. Yellow (also jumpered)
  3. Green (not jumpered)

Does anyone have any other advice on what to check?

Brown, Yellow, Red in the bottom center are jumper wires running in the direction of the outdoor condenser unit. Wiring diagram on side of indoor Rheem fan unit in attic Wiring behind thermostat

  • If I suspected that the wiring had been stressed, I'd undo and redo all the connections, one wire at a time. Remove the wire nut, check the wiring underneath and replace the nut. Back off the screw terminals, reseat the wires and retighten the screws. – mike65535 May 5 at 23:20

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