Converting LP Furnace to furnace only thermostat

[1nolaguy]

Hi All. So far the fall has been pretty mild in the mid-west (Ky & TN) but it is fixing to get very cold in a few days. This spring we had to replace both of our A/Cs and switched from Penguins to Recpro (Horton) heat pumps. So far these have worked well, although the controls are a bit wonky, but HPs only work down to about 40 deg. These have independent controls at the ceiling units and do not connect to the original thermostat that use to control the lp furnaces (we have two) as well as the original A/Cs. The tech that did the replacement placed the old "brains" from the original a/cs inside the new units and said that the furnaces would continue to work off the wall thermostat, but today I decided to test them in anticipation of the coming cold and discovered the thermostat has no power and so no control of the LP furnaces.

 

Can anyone in the group advise how best to get the furnaces going? I thought of possibly just replacing the old thermostat with a furnace only thermostat but am not sure what to do concerning the wiring. As I recall app the wiring to the original thermostat that controlled both the A/Cs and the Furnaces is connected via an RJ11 (phone plug) connection.

[klcdenver]

Go to AC,Heating and Cooling forums and look at the forum listed below and you should find your answer.

Houghton AC/Heatpump

 

[highsierra37@att.net]

 

I have an 02 dynasty with all original equipment. In anticipation of colder weather i recently placed the thermostat in the furnace mode and asked for heating to check that the furnace operated properly. The furnace did not operate. Doing some research i found that the mostly likely cause of the furnace not operating would be a faulty thermostat. I swapped the front thermostat with the rear thermostat and found that the furnace still did not operate. It would be unlikely that both thermostats were faulty so i ruled out a faulty thermostat as the cause of the problem. For the furnace to operate it requires proper propane pressure and proper 12volt power . I checked both and they were normal. With further research i found that the signal from the thermostat  goes from the thermostat to the circuit board on the roof air conditioner and then to the furnace. I removed the roof air conditioner circuit board and sent it to a company to see if there was a problem with the circuit board. The circuit board checked out as normal - we replaced a few components just as a precaution and reinstalled the circuit board . The furnace still did operate.

At the furnace there are two blue colored wires that send a signal from the furnace and circuit board for the furnace to operate.  There are disconnects about a foot from the furnace where the wires can be disconnected. If a jumper wire is connected to join the two blue wires together ,that are going to the furnace, all of the wiring from the thermostat to the furnace is eliminated. When i joined the two blue wires together the furnace started and operated as normal. This told me that the problem was somewhere between the thermostat and the furnace which was not getting a signal to operate. I decided to simplify the system and control the furnace with a simple thermostat that is directly wired to the furnace.

I could not find a place where i could mount a thermostat to control the furnace except inside a cabinet near the furnace. from the mounting location i easily ran two new wires directly to the two input wires to the furnace. The new thermostat is out of sight and during the few times the furnace is used i will keep the cabinet door open so the temperature sensing is accurate.  

It sounds like your new system should have been rewired to operate as the original so this might help with trouble shooting. I still do not know where the problem could be with my original wiring system but i like the simplified system that i now have.

Joe Klasch  02 dynasty

[Jerry G]

I believe my tech connected the blue wires bypassing the heat pump, removed the existing thermostat and connected those wires to a simple wall mounted thermostat in the same location. It works fine when we needed it.

Surprised, the Houghton has worked great down to 28-30 degrees. We've rarely used the furnace since installing. But will when colder than that.

[Tom Cherry]

16 hours ago, 1nolaguy said:

Hi All. So far the fall has been pretty mild in the mid-west (Ky & TN) but it is fixing to get very cold in a few days. This spring we had to replace both of our A/Cs and switched from Penguins to Recpro (Horton) heat pumps. So far these have worked well, although the controls are a bit wonky, but HPs only work down to about 40 deg. These have independent controls at the ceiling units and do not connect to the original thermostat that use to control the lp furnaces (we have two) as well as the original A/Cs. The tech that did the replacement placed the old "brains" from the original a/cs inside the new units and said that the furnaces would continue to work off the wall thermostat, but today I decided to test them in anticipation of the coming cold and discovered the thermostat has no power and so no control of the LP furnaces.

 

Can anyone in the group advise how best to get the furnaces going? I thought of possibly just replacing the old thermostat with a furnace only thermostat but am not sure what to do concerning the wiring. As I recall app the wiring to the original thermostat that controlled both the A/Cs and the Furnaces is connected via an RJ11 (phone plug) connection.

Couple of suggestions.

First….if you have the 5 button thermostat, then you need to make sure that you “see” the furnace setting.  If NOT, then do a system reset.  The control modules or “brains” must still receive the 12 VDC.  The wall TStat does NOT have a DC power supply.  The DC comes in via a line from a house fuse.  If there is NO DC power, then the Thermostat will not light up.  There is a DIP SWTCH on the module that tells the furnace to come ON…or more precisely, controls the on/off circuit to the furnace.  That DIP SWITCH activates the relay contacts to turn ON or OFF the furnace based on instructions from the Thermostat.  Your Front unit gets the temperature reading from the front Thermostat.  The rear one (module) gets it temperature reading from the remote sensor somewhere on the wall.

If you pull the original Penguin install and operate manual prints off the internet…they may be here…but are commonly out there, then there are instructions and also terminal callouts for the furnace.  
 

What I don’t recall is….are the two wires to furnace a switch leg….as in….you jumped them and then the furnace comes on….or does the control module send a 12 VDC signal to the furnace.  If they are a switch leg….jumpering will start the furnace.  I’d find a manual on the furnace and look at the control wiring.

You can also find the two output or switched terminals for the furnace on the module.  Use the front one,  turn on the zone 1 furnace.  Do you get a closed or continuity through the contacts or a 12 VDC signal.

that’s the basics…..

[1nolaguy]

Thanks Tom. This sounds a bit above my pay grade but I will look for the owners manual/ wiring diagram and then also check the continuity. Based on what you described The modules may not be getting 12vdc as the 5 button thermostat  does not light up at all when switched to the on position.

[Tom Cherry]

44 minutes ago, 1nolaguy said:

Thanks Tom. This sounds a bit above my pay grade but I will look for the owners manual/ wiring diagram and then also check the continuity. Based on what you described The modules may not be getting 12vdc as the 5 button thermostat  does not light up at all when switched to the on position.

BINGO....we have a WINNER.  When you said that the Furnace did not work, I did not pick up NO DISPLAY. I reread.  You did say NO POWER.  NOW try this.

Turn OFF the Thermostat.  Hold in the TOP and BOTTOM (Mode and ZONE) buttons.....and THEN, while still held in.....turn ON the thermostat.  Then the display should right up.  There will be an FF in the display.  You should be able to use the Zone and Mode to get to Furnace.  

If NO POWER....then there is an issue in ONE or BOTH of the Modules.  The Modules HAVE to have 12 VDC power.  That comes from a House Fuse.  Sometimes marked as SAT.....no rhyme or reason for what Monaco labeled it as.  The first thing is to verify that ALL the House Fuses are working.  Then look at the Brain and see WHERE the 12 VDC is supposed to come from.  If the Tech did not attach or jumper in POWER, then that is the issue.  

NOTE....if only ONE of them has 12 VDC, then that is the ONLY zone that will show.  BOTH need 12 VDC to work.  The RESET that you did verified what is DOWNSTREAM....so the Thermostat, which is semismart, should KNOW that there are TWO brains hooked up and that you have a FURNACE control activated on EACH one.  I do NOT know about how the AC and other settings will be.  That is a mystery.  BUT, the Module has to be "Working" or thinks its working like it was hooked up with the Penguins were installed.

If you can NOT accomplish that, then you MAY need to have an additional thermostat in the ceiling for heat.  THAT and the "modifications and revisions" to the Penguin system is way ABOVE my pay grade....

The new system is not, I suspect, a Multiplex system where the control modules run it and the thermostat shows you items and allows you to adjust. it.  

Let us know...