2007 Diplomat cannot get rear zone 2 furnace to work

[Coach J]

Zone 1 furnace comes on just fine but zone 2 won’t come on 

[TigerMar]

Have you tried resetting the system using the thermostat ?

[Steve P]

I just had the same problem... the breaker in my rear panel appeared fine, but I flipped it off and back on and the rear heat came on immediately.  Now the question is, was it tripped and why...?  I hope your issue is as easy as that. 

[Tom Cherry]

MOST of the time, you nave a “communications” issue,  Age is about right.  Try this before you go crazy and start “unique solutions”.

Pop off the covers for the HVAC (ceiling) panels.  There are 4 screws(memory) to remove,  you will see some phone lines with what is called a “dual inline” connector.  The phone cables carry the data and allow the system to work.  There will be 2 in the front,  probably only ONE in the rear,  I always mark how the lines are connected, but they are not polarized or such.  There is a “control” module in each AC.  It has a LINE going to the furnace.  The control module has 2 phone lines.  They have male ends.  They don’t care which way the signal goes…. There is an incoming phone line from the thermostat.  Then that goes to the front AC.  Then there is a line running to the rear AC.  There is a hard wired remote temp sensor in the rear.

TURN OFF THE THERMOSTAT….

You disconnect one connector.  Then use a QTip and alcohol or Electronic (NOT electrical) cleaner.  Clean the contacts on the male ends and the female ends in the connectors.  Then plug in…. Push hard.  Unplug and repeat a few times,  DO all phone lines.

NOW, go to the Thermostat.  Hold IN the Mode and Zone buttons…..while holding them….turn on the Thermostat.  That is a hard reset.  You should see FF in the display.  Odds are….the furnace in Zone 2 will work.  If NOT, you have eliminated the most common “a zone or a zone function will not work”.

I would.NOT do any troubleshooting until you have cleaned the communications lines.  They are notorious for working when you leave home….and then NOT working when you set up.

Try that and report back.

[Coach J]

Let me rephrase. Furnace will come on in zone 2 and run about 10 seconds with cool air and then go off. I don’t think it’s a thermostat issue. 

[Reka52]

Check the sail switch in furnace 2 and clean check exhaust tube and igniters

[Flyinhy]

I haven't had my coach very long but for the last 2 winter seasons I have to "bleed" my heat exchangers when that happens. Especially the living room. The fans will come on but no circulation from the pumps.

[Tom Cherry]

4 hours ago, Flyinhy said:

I haven't had my coach very long but for the last 2 winter seasons I have to "bleed" my heat exchangers when that happens. Especially the living room. The fans will come on but no circulation from the pumps.

Mixing models and types of heating systems here.  The OP has a 2007 Diplomat with dual (from research on IRV2) furnaces.  Front and Rear.  The Diplomat did not have a hydronic (AquaHot) option.

The Executive has likely has a hydronic (AquaHot?) system that used individual "radiators" or heat exchangers, within in specific zones, with a special heated boiler "antifreeze" circulating....Therefore the issues of a furnace not working are related to a propane fired rear furnace or zone 2.

Just want to keep this topic clarified so the comments are pertinent.  Thanks

[Chuck B 2004 Windsor]

There are 2 blue wires coming from the heater.  A contact closure aka short on the wires will turn on the furnace.  Get a mechanical thermostat .  Mount it above the furnace.  Run the 2 blue wires to the thermostat.  

Chuck B 2004 Windsor

[Steven P]

I've had the same issue w my rear furnace since I bought the coach.  We have very little cold weather usage so I haven't pursued it very far.  I did find the sail switch to be failing 2 years ago and fixed that.  After that it would light and blow luke warm air which was better than none.  Last winter I couldn't get it to stay lit.  It would ignite and give warm exhaust 3 times then the flashing lights indicate ignition lockout fault.  That's as far as I've gotten.  @Coach J if you look at the furnace from the outside, there is an led light that flashes giving a code.  See what you get there. 

[Tom Cherry]

23 hours ago, Chuck B 2004 Windsor said:

There are 2 blue wires coming from the heater.  A contact closure aka short on the wires will turn on the furnace.  Get a mechanical thermostat .  Mount it above the furnace.  Run the 2 blue wires to the thermostat.  

Chuck B 2004 Windsor

Yes, that is ONE way to fix it.....but I wonder (highly SUSPECT)  if the issue is really INSIDE the furnace.  The logic of the Dometic Thermostat is that when you put Zone 2 into FURNACE, then that "tells" the Control Module in the AC unit (on the TOP SIDE) to use the Rear Zone Remote sensor for temperature control and to SIGNAL the furnace to RUN.  Since the Furnace is coming ON....(Fan blowing) then the Thermostat and the Remote Sensor and the Control Module in the rear HVAC are performing or working as they should.  Thus, my "communications" failure fix was NOT needed.

IF there was an issue with the thermostat or the control module and one wanted to BYPASS them, then the two wire "Remote Thermostat" solution might be a viable one.....depending on how much of an issue the normal or factory circuit was to repair.

BUT....it is coming on.  SO, the system is working.  That also means, as a matter of superflous information, that the HEAT/Furnace Dip Switch is in the ON position on the control module.

I think that Ivan is on to it.  The furnace has SOME issue that is not allowing its INTERNAL (NOT THE Duotherm control circuit) Circuit Board to function properly and that is the REAL problem.  Whether the Sail Switch (a likely candidate as they are supposed to be idiot proof...but often are malfunctioning) or the firing (ignition) circuit or the ignition module is not working.  MOST propane (or NAT GAS) systems have the same time tested interlock.  You have to have ON a pilot.....or an igniter to IGNITE the pilot.  There is a thermocouple (Bulb on a long copper small tube....which is a capillary device) that must heat up.  That verifies that you DO have a PILOT light or burner with a FLAME.  THEN, the controller will allow the Main GAS valve to OPEN and you get full gas flow and the burner is LIGHTED.  Should the Pilot go out....then the control board will shut down the MAIN Valve or the control valve to the burner gas supply.

I would download the manual (Atwood?)  There will be a trouble shooting guide in it as well as an explanation of the logic.  It is NOT uncommon for the Capillary tube thermocouple to FAIL....    That is the MAIN failure item on most natural gas or propane fired home gas logs and almost all the big boxes like Lowes and HD and Ace carry them.  Past that, you have the MAIN control board in the furnace as well as the Igniter.  The sail switch (the blower is running) and the Thermocouple and the igniter and the main gas valve are the ONLY components....generically speaking in the system.  There MAY be (is) a HIGH Temp thermocouple....I SUPPOSE, if there is and it has CORRODED and is CLOSED....then it will prevent ignition.  Read up on it....

Follow the trouble shooting logic and instructions.  When you get it working, please give the forum some feedback.

Thanks and Good Luck...

[Coach J]

On 12/23/2022 at 9:53 PM, Tom Cherry said:

MOST of the time, you nave a “communications” issue,  Age is about right.  Try this before you go crazy and start “unique solutions”.

Pop off the covers for the HVAC (ceiling) panels.  There are 4 screws(memory) to remove,  you will see some phone lines with what is called a “dual inline” connector.  The phone cables carry the data and allow the system to work.  There will be 2 in the front,  probably only ONE in the rear,  I always mark how the lines are connected, but they are not polarized or such.  There is a “control” module in each AC.  It has a LINE going to the furnace.  The control module has 2 phone lines.  They have male ends.  They don’t care which way the signal goes…. There is an incoming phone line from the thermostat.  Then that goes to the front AC.  Then there is a line running to the rear AC.  There is a hard wired remote temp sensor in the rear.

TURN OFF THE THERMOSTAT….

You disconnect one connector.  Then use a QTip and alcohol or Electronic (NOT electrical) cleaner.  Clean the contacts on the male ends and the female ends in the connectors.  Then plug in…. Push hard.  Unplug and repeat a few times,  DO all phone lines.

NOW, go to the Thermostat.  Hold IN the Mode and Zone buttons…..while holding them….turn on the Thermostat.  That is a hard reset.  You should see FF in the display.  Odds are….the furnace in Zone 2 will work.  If NOT, you have eliminated the most common “a zone or a zone function will not work”.

I would.NOT do any troubleshooting until you have cleaned the communications lines.  They are notorious for working when you leave home….and then NOT working when you set up.

Try that and report back.

Can you please tell me if this continues to be an issue will changing the connectors is a fix?  I cannot seem to get through a trip without losing zone 2 of my system. It worked just fine for the last few days and now all of a sudden zone 2 is gone again 

[Tom Cherry]

12 hours ago, Coach J said:

Can you please tell me if this continues to be an issue will changing the connectors is a fix?  I cannot seem to get through a trip without losing zone 2 of my system. It worked just fine for the last few days and now all of a sudden zone 2 is gone again 

Per our OFFLINE (which is good) PM's, you now understand the system better.  The phone lines that run from the thermostat to the front unit and then from the front to the rear (or if you have middle one....through it) are a Multiplexed Data Buss.  That data buss runs this way

Thermostat via phone line to front unit.  THEN up into the Control Module (on the outside).

Back down from the Control Module and then via the phone line going to the rear.....into the Rear Control Module.  There is NO outgoing signal used from that module....as it is the "End of the Line"

Anytime there is an "open or partially open" circuit in that data buss (the phone lines) or a component such as the Control Modules....then the Thermostat says....I DON'T KNOW YOU PEOPLE or WHERE is ONE that used to be there.....  Then the Thermostat has to be RESET....establish communication with all the lines and the components and get an OK....  So, if one component or a line has a nick or is just barely making contact....the Thermostat drops OUT that one.  In your case.... the REAR.

I lost my Rear (OK....LAUGH) one and fixed it by cleaning and plugging and such.  That lasted for 4 years.  I ordered new connectors and stored them in my spare parts.  SO WELL, I NEVER FOUND THEM....  Then when it happened again....I had to clean....twice....and it was 100 DF and my DW and GD were NOT happy campers.  That was 2 years ago.  I reordered...and THEN found my spares...so I have TWO.  WHEN (not IF) I lose connections again....NEW ONES go on.

Rarely do we see a Control Module issue...but it DOES happen.  Most likely is a BAD Phone connector on a line.  The list is endless.  You can swap the front to the rear Control Module and you have to make ONE dip switch setting....and then if you lose the FRONT.... BAD module.

Good luck....

[Chuck B 2004 Windsor]

Remember there are 2 types of so called phone lines, voice, and data.  The wire positions at each end of the plug determines if it's a phone line or a data line.

Chuck B 2004 Windsor

[Chuck B 2004 Windsor]

I forgot to add that any flat cable over 13 feet from one device to another is subject to cross talk.  Better to use 2 or 4 pair JKT because it has twisted wires in the cable.

I replaced all the flat cable in my coach with JKT.  I never had any more problems.  You will not have cross talk problems with a multiplex system.

Chuck B 2004 Windsor