Old-Biscuit wrote:

That On/Off CB Switch has 3 wires
RED and BLUE on one terminal and then RED on other terminal

RED/Blue....red is 12VDC + from DC Dist Panel (FUSED)
Blue sends 12VDC+ to the thermostat

RED on other side goes to Timed Delay Relay.
When Thermostat closes then 12VDC+ goes to coil side of Timed Delay Relay which allows the 12VDC+ on RED to go to Fan Motor

So you should have 12VDC + on RED/Blue at the On/Off Switch and on the RED from Switch to the Time Delay Relay (Green Box)

Yellow is NEG/Ground

Old-Biscuit wrote:

Connect the 2 blue wires togther.furnace should come on
Connect the blue wire (one from furnace on/off switch) to Yellow wire and A/C Unit should come on

BFL13 wrote:

you can confirm the furnace works down at the furnace by jumpering the blues that would go to the tstat (but somehow get to the red and white on yours I think)

dougrainer wrote:

1. You have NOT removed all the wires from the hole for the Tstat.
2. You will NOT have "blue" wires at the tstat. The Blue wires are the 2 just for the furnace AT the furnace that go to the wall tstat and return
3. Most OEM's use standard home type Tstat multistrand wire to connect the Roof AC and to the furnace.
4. Usually they use the small 20 gauge wires---red and white to go from the furnace to the wall tstat.
5. When you have your type tstat, the one blue wire at the furnace that is 12 volt, it goes to the Roof AC control board in the AC. THAT wire is what supplies 12 volt power to the Roof AC control board and then DOWN to the wall tstsat. On other models, the blue 12 v wire goes to the wall tstat and then another wire then feeds the Roof AC for 12 volt power to the Roof AC. You need to get all the wires out of that small hole in the wall and odds are you will see a wire not connected. Doug

rejesterd wrote:





Ok, I'm slowly getting this. I've actually looked at the manual Old-Biscuit linked before, but I don't have 2 blue wires. Here's the thermostat wiring.



So there's one of each: blue, red, white, yellow, gray, and green. It's hard to see from the picture, but there is also another red wire inside the wall that is connected to another very small gauge red wire with a wire nut. Neither of these appear to be connected to the thermostat. Also, there are 2 purple wires coming from the thermostat that have been cut and taped over. I haven't done anything to the wiring here, so this is the way it's been for years (and the system has worked generally well for the most part).

Based on what I'm reading in the manual, it seems that if I connect red to green or red to gray, that should operate the fan only. And connecting red to yellow & green, that would operate the AC at low speed. And connecting red to white would run the furnace.

Is that correct? Thanks so much.

BFL13 wrote:

Did you put your voltmeter on the AC control box shown in that photo for any 12v there? With and without the tstat control to "on" for that? Those terminals look easy to get the meter probes on, unlike at that tstat circuit board without doing any harm touching the wrong thing.

dougrainer wrote:

Your original tstat wall pic shows a large 14 gauge RED wire connected to a small 20 gauge red wire with a wire nut inside the wall hole. THAT wire should have 12 volts pos. Doug

BFL13 wrote:

What do you mean by "shore power"? That is 120v. Furnace is all 12v. A/C has 120v but controls for it are 12v.

dougrainer wrote:

You screwed up big time You attempted to use the Tstat mount screw for a ground????? How would that be a ground screwed into WOOD? Find another ground source. Now that SMALL 2 wires(Red and White), those come from the Furnace. See your pic. The RED should be 12 volt positive at the furnace and at the wall tstat. Once you get a good ground verify that at the tstat. Doug

PS a Ground should be that Large BLUE wire at the wall tstat. BUT, if that wire has lost its ground, that would be your power problem, so it is best to use a good ground from another source. I usually use the GROUND pin on the 120 wall receptacle.