Cut Wire at Furnace

[George]

Please help me figure out if this a problem or not. The furnace works but I have found a cut wire from the thermostat.
At the furnace there is a pair of wires from the thermostat. Both of these RED and WHITE wires are crimped to the furnace BLUE wire. The WHITE wire has been cut, see attached photo.
.
The t’stat wiring diagram labels the RED as +12VDC and the WHITE as FURNACE.
The furnace wiring diagram labels the BLUE wire as THERMOSTAT.
The furnace BLUE/WHITE wire is not connected to anything. Labeled POWER TO THERMOSTAT.
Should this WHITE wire be repaired?
.
I might mention that all 3 butt splices were tucked into the squirrel cage and the -12VDC splice was worn through. The white wire may have been cut by the squirrel cage but it seems unlikely.
If you're wondering why I have the cover off – I'm painting it. Suburban's idea of weatherproof paint leaves something to be desired. Chalked up after <2 years.
I've also sent this to Alliance Service and will post any response from them as I receive it.

 

[George]

Update: Alliance contacted me and advised repairing the white wire. I did so and the furnace fires and shuts down as expected.
I replied that I am still confused as to why the RED *and* WHITE wires are both terminated to the furnace BLUE wire. I also asked where typically this 2-conductor cable is spliced into the 6-conductor from the thermostat – at the rooftop A/C?

 

[George]

Update to Update: 🙃
Alliance Service confirms that the 2-conductor cable picks up the white wire from the thermostat at the rooftop A/C unit.
I haven't climbed up there but I suppose they just used both the RED and WHITE for redundancy. This actually saved me from an inoperative furnace since the white wire was cut.
May I add that replies from Alliance were timely and appreciated.

 

[brytonmar]

I'm diagnosing a similar issue with my 2023 382RK. I found the white thermostat wire cut and it doesn't appear to have ever been connected with the red and blue and appeared to be taped off with masking tape. I also found the blue/white wire which is hot at 13.7V from the motherboard, cut and just sitting outside the hole to the left of the heater box. I have not been able to get the blower to come on since the thermostat was tested not working by a technician a couple of years ago. The new thermostat drives the air conditioner, but not the heater, suspecting it is one or both of the wires that is the problem. If I touch the blue/white wire to the blue/red thermostat wire, the blower comes on. Trying not to fry anything, does anyone have a suggestion where the wires need to be hooked up? I could hook the white wire to the red and blue like this thread suggests, but I have no guess where the blue/white wire needs to go.

 

[brytonmar]

Looks like I probably just need to hook the white wire to the red and blue. The blue/white looks like it's not used and may be there to bypass the thermostat when needed although it's scary that a hot wire was just laying outside the box and not taped off. Waiting for reply from Alliance, I'll post if anything different from just hooking up the white wire. The white wire is hooked up to the thermostat in the correct place.

 

[George]

I spent 30 minutes composing a long trouble shooting procedure and my computer froze up and I lost it. 🤬
In any case what you describe doing is probably correct.
My white wire was in the crimp but cut above it so I felt comfortable just reconnecting it. Maybe you should look inside roof AC to see what happens to the brown wrapped 2-conductor cable and the white wire in the 6-conductor cable from the thermostat.

 

[dwcfish]

I don't know if this will help you, I had to replace the blower motor on my heater a while back and this was easier if I pulled the furnace out. I always take pictures of things as I am taking them apart. Here are the Pics of the wires. Note on the brown wire coming from the Tstat you can just see a wire sticking out that is not used.

 

[brytonmar]

Today I opened up the air conditioner and found the white wire not connected. The red wire is tapped into a hot 12V pink wire and I think the red wire in the 2 wire red/white bundle that goes to the heater was not hooked up either. The air conditioner works fine and the heater works great when it gets power. What I did was hooked the white together (you can see the grey wire nut in pic) and hooked both loose ends of the red wire to the tap. This energizes the blower even if the thermostat is off. Looking at the 3 pictures dwcfish posted, I don't see the white wire in his 2 wire bundle, just the red to the blue, how I found mine. I'm still scratching my head tonight, I'm thinking maybe unhook the white wire from the red into blue at the heater and try that. Bottom line, I need to get the thermostat to control the 12V signal to the heater and I'm at a loss how to accomplish that.

 

[BryanValRox]

Today I opened up the air conditioner and found the white wire not connected. The red wire is tapped into a hot 12V pink wire and I think the red wire in the 2 wire red/white bundle that goes to the heater was not hooked up either. The air conditioner works fine and the heater works great when it gets power. What I did was hooked the white together (you can see the grey wire nut in pic) and hooked both loose ends of the red wire to the tap. This energizes the blower even if the thermostat is off. Looking at the 3 pictures dwcfish posted, I don't see the white wire in his 2 wire bundle, just the red to the blue, how I found mine. I'm still scratching my head tonight, I'm thinking maybe unhook the white wire from the red into blue at the heater and try that. Bottom line, I need to get the thermostat to control the 12V signal to the heater and I'm at a loss how to accomplish that.

Maybe this will help you some. It is a service manual for many Suburban Furnaces.

 

[brytonmar]

Thanks for posting the service manual. Head is spinning from information overload. By hooking the red wire to the 12v tap wire (both the 18/6 and 18/2 wire bundles), it seems like it creates a full time power loop which explains why the blower fan comes on even when the thermostat is set to off. Just in this thread, we have the red and white wire hooked to the blue wire at the furnace and then just the red wire hooked to the blue wire with the white wire cut and not hooked up just as I found mine. Very confusing. My pea brain is telling me to cut the red wire at the furnace, as the red wire is always hot from the 12v tap at the air conditioner. Leaving the white wire to get the 12v from the thermostat when set to heat and temp set above ambient. The manual is showing 24v to the white wire at the control board, which confuses me even more. I'm going to other projects today unless someone has the answer, which I'll gladly try. I've got a request in for Alliance, hopefully a tech can get this straightened out for me next week. I live in Yuma AZ, so it's not a pressing issue since it's still 90+ here, but now this is consuming me.

 

[George]

I cannot explain why the 18AWG red wire is tapped into the PINK/WHITE wire. The P/W is the main power for the furnace. Connecting the 18/2 RED to it will, as you say, cause the furnace to run regardless of the t'stat.
If it was me...
At the AC leave 18/2 RED wire disconnected.
At the AC connect the 18/2 WHITE wire to the 18/6 WHITE wire.
At the furnace leave the 18/2 RED wire disconnected.
At the furnace connect the 18/2 WHITE wire to the furnace BLUE wire.
At the furnace leave the furnace BLUE/WHITE wire disconnected.

 

[brytonmar]

I haven't gone deep into the A/C unit service manual, I'm thinking it has both 120V and 12V and the 12V for the thermostat has to come from somewhere. Your thinking on the 18/2 wiring is just like mine, but that doesn't look like anything else we've seen in the pictures in this thread.

 

[BryanValRox]

Thanks for posting the service manual. Head is spinning from information overload. By hooking the red wire to the 12v tap wire (both the 18/6 and 18/2 wire bundles), it seems like it creates a full time power loop which explains why the blower fan comes on even when the thermostat is set to off. Just in this thread, we have the red and white wire hooked to the blue wire at the furnace and then just the red wire hooked to the blue wire with the white wire cut and not hooked up just as I found mine. Very confusing. My pea brain is telling me to cut the red wire at the furnace, as the red wire is always hot from the 12v tap at the air conditioner. Leaving the white wire to get the 12v from the thermostat when set to heat and temp set above ambient. The manual is showing 24v to the white wire at the control board, which confuses me even more. I'm going to other projects today unless someone has the answer, which I'll gladly try. I've got a request in for Alliance, hopefully a tech can get this straightened out for me next week. I live in Yuma AZ, so it's not a pressing issue since it's still 90+ here, but now this is consuming me.

So, this manual cover several different furnaces and applications. The 24 volt reference is for a 24v AC application.
When you are reviewing the info. In the Manual you need to be sure the data table, chart or diagram is calling out a 12 DC reference that we have in our coaches.

 

[brytonmar]

I think I got this thing figured out. Used the 12V tap to the Red 18/6 wire at the AC. I hooked the white 18/6 wire to the red 18/2 wire. I have both the white and the red 18/2 wires hooked to the blue wire at the heater although the white 18/2 to the furnace is not hooked to anything at the AC so is not needed. Everything is functioning through the thermostat as it should be. Thanks for all the help and hopefully this helps someone else in the future.

 

[BryanValRox]

Glad to hear you have it figured out!

Congratulations on your project!

 

[George]

Way to go. 👍🏼