SOLVED: No power getting to the thermostat

rejesterd wrote:

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)

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.

YES!

As a side note, I would be scared of how the wires are on that tstat circuit board too easy to break something can't be fixed, so I would snip the wires half way up to leave length and wire nut them back together after.

That way no chance of breaking anything right at the circuit board and no chance of mixing up the colours, and--it is easy to put a meter on any two and for putting the ends together of the ones coming out of the wall for trying to see if anything makes the furnace work--and without shorting something on the circuit board can't be fixed.

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

Thanks Doug. The thermostat wiring shown in the above pic is the way it's always been. I've looked at it before and made notes about the wires and colors. If I look further in the wall hole, I can also see a black wire, and that one additional red wire that has a wire nut on it (with a very small gauge red wire connected to it).

Here's my AC control box..



I cleaned up these connections when I first noticed the problem a couple days ago. From left-to-right, the colors are yellow (Y), gray (GL), green (GH), and blue/white connected together (B).

Based on what you're seeing, what would you check next?

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

I don't know which wires do what in that photo, but before removing any, make very sure you know where each goes for when putting it back!!

I think you need to find the place up where the relay is for the air conditioner to see if there is 12v at that location. I got the idea the 12v for the tstat comes from up there where a click can be heard, but not sure. The pros here will be able to say what to do now.

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)

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.

13V on Blue wire..that goes to the thermostat
Remove cover on thermostat
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

Thermostat is bad if in Cool or Heat modes A/C or Furnace do not work


See pg 14 and 15....Flow chart for Heat Mode and Cool Mode
Coleman Thermostat Info

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

I have 13V at the 2 red wires and the blue wire shown in the above picture. Not sure what to check next.

I forgot to mention that the AC nor the fan for the AC work either.

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

You need a ground to get the 12v on a meter at the tstat, The two blues from the furnace are actually cut and joined at the tstat switch in a heat only. with an air conditioner it seems the wires all go to a relay up thee and back so it is red and white. Anyway, 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)

Too confusing, but here is a thread on that that might help including links to trouble shooting.

https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/30000743/srt/pa/pging/1/page/4.cfm