New thermostat question?

Gonna check tomorrow on the A/C. The identifying labels on this camper disappeared long ago. Thanks for the stat. Check in tomorrow.

Your system should be set up for the A/C to use 12 volt control off the power from the furnace.

Do you have a coleman AC , you never said
You could mount the cool only stat close and run the wires behind not drilling a hole , wire it make sure it works first
Heres a cool only stat for coleman , analog , you already have a digital room temp on the other one .
Make sure your AC is on the list of compatible ones

https://www.pplmotorhomes.com/parts/rv-appliances/air-conditioner/air-conditioner-parts-accessories/mach-8-heat-pump-15k-bk_61357

@ amazon

https://www.amazon.com/Airxcel-69-1247-T-Stat-Wall-Analog/dp/B00KPR3T9M/ref=sr_1_1?dchild=1&hvadid=77928006825257&hvbmt=bp&hvdev=c&hvqmt=p&keywords=7330f3361&qid=1606083705&sr=8-1&tag=mh0b-20

Okan-Star were going with your plan! My job is to climb up on the roof and verify the A/C model as well as drill a hole and run some wires. Garrett will hook it up. Again you guys were great and knowledgeable. I'll let you know how it turns out.
Joe

Speaking to my friend Garrett this morning, he threw out this problem on one of his HVAC forums and the idea of just replacing the motor and the board would do the trick to change it to a single stage furnace. They all agreed the A/C really doesn't matter and that could just run on low. That would give me any one of hundreds of stat's and the wiring would be similar but changed to run on low. He is not sure about this angle but he said the motor is about 150 bucks and the board about 80. I'll show him this thread this afternoon. I told him I am leaning towards the info on this thread. Keep in mind this is the first time Garrett has ever worked on an RV. Thanks for all the info, Joe

towpro wrote:
I have never tried to put a home thermostat in a system like you have, but its easy to figure out.

Again, I only see 1 wire involved in HEAT, so I believe the 2 stage heat is done 100% based on time, and it controlled by heater mother board. I do recall when I had this system (year ago), when you started it after getting to camp ground on cold night the heat would come on low, than after a couple minutes switch to high until temps were satisfied, then turn off. than the rest of the night it would just run on low because normal heat never allowed heater to run long enough to hit the timeout that starts state 2 heat.



First, I am not responsible for any damage you do, this is purely for entertainment proposes.

The AC jumper for coleman is between 3 and 4 pin providing 12vdc to comp and fan
Its between 2 and 3 for dometic for 7.5 v
But the AC is the easy part to understand

2nd. I do see on page 15 they have Two different systems, one uses wire 6 wires, and one uses 7.
the 7 wire appears to be of you have a Colman AC it uses wire 2 which is 7.5v no idea what that is for.
my logic below only applies to 6 wire system.

Your new digital home thermostat:

the logic on a home thermostat is as follows:
When you have a call for heat, the thermostat closes a "Heat relay" that connects terminals C and W, and heat comes on.

when you have a call for AC, the thermostat closes a "compressor contractor relay" that connects C and Y. and the AC comes on.

it can also control relay "fan relay" which connects terminals C and G.
Don't worry about the 24Vac, this is not needed by thermostat (more later on that)

From the wiring diagram in document, here is what I see your system has.

1= 12Vdc ground
2= not used
3= 12Vdc positive (appears to come from heater)
4 = not shown
5 = compressor turn on (to AC)
6 = Hi fan turn on (to AC)
7 = Low fan turn on (to AC)

The first step is to find out what your current thermostat does to wires 5, 6, 7 and 8 to cause those features to turn on.

You can use a meter to test this.

Turn the heater on (if thermostat works)
using volt meter, with heater running check voltage between wires 3 and 8. we know 3 is 12V positive, and we know 8 is the "turn on wire" to heater.
With heater running, if you show 12V between wires 3 and 8 we know the thermostat is applying 12v- (ground) to wire 8 to start heater.

If you show no voltage, then check between wires 1 and 8.
Since 1 is 12v negative (ground) if you see voltage between 1 and 8 we know that the thermostat is connecting 12V + to wire 8 to turn on heater.

Now test the voltage between 3 and 5 with AC on, do you see 12V? if yes, thermostat is grounding 5 to turn on AC compressor

now do same test for wires 6 and 7, to see how the thermostat turns on fan.

I am betting this thermostat is grounding wires to turn on AC, heat and fan. if this is true here is how I would wire home digital thermostat.

set new thermostat for 1H1C (single stage heat, single stage cool).

I am using wire numbers from old thermostat since I don't know the real colors.
remove all jumpers for new thermostat.

1 = 12Vdc Ground goes to new thermostat terminal Blue or black C or common.
3 = 12V positive is not used, tape up end so it don't tough any thing inside thermostat.
8 = Furnace turn on wire goes to new thermostat terminal white W heat
5 = compressor turn on wire goes to new thermostat yellow - Y air conditioner

6 - high fan to AC
7 = low fan to AC

Fan control:
there is several ways to go here. First the thermostat can only turn on 1 fan, so you can add a small small single pole, double throw switch to change between Hi and Lo.
Take the thermostat fan output and attach it to the center pin of a SPDT switch. than attach #6 to one outer pin and #7 to other outer pin. this allows you to switch between High and Low fans. find a space on bottom of side of thermostat to mount this switch.
or just attach wire 6 to new thermostat and AC will only have high fan.

Now what do we do to this wire off center of SPDT switch to control fan? that depends:

Most better digital thermostats will have a setting for "heater controls fan" or on some call it "gas heat" mode.
this means that the thermostat will NOT turn on G (Fan relay) for heat, but will turn on G (fan relay) for AC. If this is the case, you can wire you fan to G terminal. this allows you to turn the AC fan on and off by fan switch on face of thermosate.

If you want the AC fan to cycle on and off every time your propane heater starts, set thermostat to "thermostat controls heater fan" and use terminal G. (this can distribute hot air from propane heat better through coach).

If your thermostat does not have the choice for "do not turn fan on for heat" and you only want ac fan to come on and off with AC, wire your fan switch to terminal Y, but this will cause fan switch on thermostat to not function.

Now if the old thermostat is switching 12V positive to every wire above to start the features, I would change to this wiring:
1 = 12Vdc negative (ground) wire is not used
2 = 12Vdc positive wire goes to new thermostat terminal Blue, or black C or common.


your new digital home type thermostat has batteries inside that control the display as well as the relays. it does NOT need 24V to function. in fact they try to NOT make thermostats that use the 24V to functions as it can cause "issues" in larger complicated home type systems.
BUT on the other hand Ecobee thermostats need the 24Vac to run so you can't use them in your RV. It appears nest has a rechargeable battery you can charge with USB, or just run a AAA alkaline battery in it.

The AC jumper for coleman is between 3 and 4 pin providing 12vdc to comp and fan
Its between 2 and 3 for dometic for 7.5 v
But the AC is the easy part to understand

That makes sense except that it actually switches between high and low based on the temp that its set at and the temp reading , its like if its 2 degrees diff it goes to low , more than that its in high then goes to low when its reaches a 2 degree difference until the seting and temp reading are the same then off ,this is in auto mode .
The mode set button scrolls from auto mode to low fan and heat mode(fixed never changes), high fan and heat( fixed ), and low fan only , high fan only. Doing this with one wire I`m not in any way an elec engineer ,but how , I can see it if its sending signals to the dual controller kind of like the fault codes that the furnace has , like two blips for one mode three for another

I would think in some way the furnace could be rewired past the dual controller to work in some fashion , but if to much is changed or if the fault system is involved it may be worth changing out the furnace to a new one stage just for safety and Ul label and all.

I just 5 years ago bought this system , it works great , its very quiet in low and when its real cold out it dosent cycle on and off like some do , mine still works knock on wood

notsobigjoe wrote:
Thanks! Is the stat your showing me the same as mine? It sure looks it but the wires are thicker and mines a dual stage. If I can do this it would be great. Actually, I'll have my Hvac friend Garrett take a look at your post. I can afford that... LOL Thank you very much my friend, I'll let you know how I make out.

Yes my heater is 2 stage , same stat , your is 15btu 22btu furnace, mine because of larger area inside 5th wheel ,is a 25btu 40btu , but thermostat is the same
The wires are of different size I would guess because Lance wired yours and the wiring on mine came with the furnace , pos and neg colors of yours are red and white , mine are red and green as shown in attwoods wiring diagram , thats not going to matter , show your buddy page 13 and 15 of the second link towpro gave.
If your stat is just failing on the AC side , but works the heater a second stat is cheaper than replacing the heater to get a new stat that will operate both , just remember to turn one off and the other on or the AC will come on to lower the room temp that the heaters rising , vis versa.
If your AC is a coleman the 2 pages below are from the coleman/airxcel analog stat I put in my Lance TC , its for a AC and single stage furnace, but the make them for AC only ,the only difference I see is the low fan wire on yours is blue and they call it gray ,not going to matter. you would have to extend the yellow , small blue and green wires , add a jumper from the pin 3 -red wire on the exiting stat to the new one for 12vdc+, I dont think you need the 12vdc- except if its used for a furnace

IF you call airxcel with the model AC you have they can confirm the cool only stat you need , If its a dometic still the same sort of thing but their stat

I have never tried to put a home thermostat in a system like you have, but its easy to figure out.

Again, I only see 1 wire involved in HEAT, so I believe the 2 stage heat is done 100% based on time, and it controlled by heater mother board. I do recall when I had this system (year ago), when you started it after getting to camp ground on cold night the heat would come on low, than after a couple minutes switch to high until temps were satisfied, then turn off. than the rest of the night it would just run on low because normal heat never allowed heater to run long enough to hit the timeout that starts state 2 heat.

First, I am not responsible for any damage you do, this is purely for entertainment proposes.


2nd. I do see on page 15 they have Two different systems, one uses wire 6 wires, and one uses 7.
the 7 wire appears to be of you have a Colman AC it uses wire 2 which is 7.5v no idea what that is for.
my logic below only applies to 6 wire system.

Your new digital home thermostat:

the logic on a home thermostat is as follows:
When you have a call for heat, the thermostat closes a "Heat relay" that connects terminals C and W, and heat comes on.

when you have a call for AC, the thermostat closes a "compressor contractor relay" that connects C and Y. and the AC comes on.

it can also control relay "fan relay" which connects terminals C and G.
Don't worry about the 24Vac, this is not needed by thermostat (more later on that)

From the wiring diagram in document, here is what I see your system has.

1= 12Vdc ground
2= not used
3= 12Vdc positive (appears to come from heater)
4 = not shown
5 = compressor turn on (to AC)
6 = Hi fan turn on (to AC)
7 = Low fan turn on (to AC)

The first step is to find out what your current thermostat does to wires 5, 6, 7 and 8 to cause those features to turn on.

You can use a meter to test this.

Turn the heater on (if thermostat works)
using volt meter, with heater running check voltage between wires 3 and 8. we know 3 is 12V positive, and we know 8 is the "turn on wire" to heater.
With heater running, if you show 12V between wires 3 and 8 we know the thermostat is applying 12v- (ground) to wire 8 to start heater.

If you show no voltage, then check between wires 1 and 8.
Since 1 is 12v negative (ground) if you see voltage between 1 and 8 we know that the thermostat is connecting 12V + to wire 8 to turn on heater.

Now test the voltage between 3 and 5 with AC on, do you see 12V? if yes, thermostat is grounding 5 to turn on AC compressor

now do same test for wires 6 and 7, to see how the thermostat turns on fan.

I am betting this thermostat is grounding wires to turn on AC, heat and fan. if this is true here is how I would wire home digital thermostat.

set new thermostat for 1H1C (single stage heat, single stage cool).

I am using wire numbers from old thermostat since I don't know the real colors.
remove all jumpers for new thermostat.

1 = 12Vdc Ground goes to new thermostat terminal Blue or black C or common.
3 = 12V positive is not used, tape up end so it don't tough any thing inside thermostat.
8 = Furnace turn on wire goes to new thermostat terminal white W heat
5 = compressor turn on wire goes to new thermostat yellow - Y air conditioner

6 - high fan to AC
7 = low fan to AC

Fan control:
there is several ways to go here. First the thermostat can only turn on 1 fan, so you can add a small small single pole, double throw switch to change between Hi and Lo.
Take the thermostat fan output and attach it to the center pin of a SPDT switch. than attach #6 to one outer pin and #7 to other outer pin. this allows you to switch between High and Low fans. find a space on bottom of side of thermostat to mount this switch.
or just attach wire 6 to new thermostat and AC will only have high fan.

Now what do we do to this wire off center of SPDT switch to control fan? that depends:

Most better digital thermostats will have a setting for "heater controls fan" or on some call it "gas heat" mode.
this means that the thermostat will NOT turn on G (Fan relay) for heat, but will turn on G (fan relay) for AC. If this is the case, you can wire you fan to G terminal. this allows you to turn the AC fan on and off by fan switch on face of thermosate.

If you want the AC fan to cycle on and off every time your propane heater starts, set thermostat to "thermostat controls heater fan" and use terminal G. (this can distribute hot air from propane heat better through coach).

If your thermostat does not have the choice for "do not turn fan on for heat" and you only want ac fan to come on and off with AC, wire your fan switch to terminal Y, but this will cause fan switch on thermostat to not function.

Now if the old thermostat is switching 12V positive to every wire above to start the features, I would change to this wiring:
1 = 12Vdc negative (ground) wire is not used
2 = 12Vdc positive wire goes to new thermostat terminal Blue, or black C or common.


your new digital home type thermostat has batteries inside that control the display as well as the relays. it does NOT need 24V to function. in fact they try to NOT make thermostats that use the 24V to functions as it can cause "issues" in larger complicated home type systems.
BUT on the other hand Ecobee thermostats need the 24Vac to run so you can't use them in your RV. It appears nest has a rechargeable battery you can charge with USB, or just run a AAA alkaline battery in it.

Thanks! Is the stat your showing me the same as mine? It sure looks it but the wires are thicker and mines a dual stage. If I can do this it would be great. Actually, I'll have my Hvac friend Garrett take a look at your post. I can afford that... LOL Thank you very much my friend, I'll let you know how I make out.

I`m guessing you have a coleman /airexel AC judging from the yellow jumper going from the 3rd pin to the 4th pin

Your small blue wire on pin 7 is the high fan ac wire
green wire on pin 6 is low fan ac
yellow on pin 5 is ac compressor wire
Disconnect those and remove the yellow jumper wire

Buy a cool only coleman stat (cheaper) or a heat and cool -only use the cool function
Hook those wires to the new stat , possible you may need to jump the 12v neg wire on pin 1 to the new stat but I think thats only for heat

pic of 2 stats in my 5th wheel- notice only 3 wires connected

In my Lance TC I have a attwood single stage heater and a coleman AC connected to a coleman stat