Dometic Analog Thermostat

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Weewun

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My neighbor has a Coachmen 5th Wheel that has two A/C's w/o heat pump and one gas furnace.  The B/R A/C works fine.

The Rear A/C and furnace do not work.  The Fan will turn on but neither the A/C nor Furnace will start when Thermostat is switched to either Cool or Furnace.  While I believe I know what the problem is and I do have another Thermostat to compare, it would be helpful if some out there had a Wiring Diagram for such Tstat or can direct me to a source that has them.

I am going over in the morning to look at it, all input appreciated.
 
It seems to me that if the fan comes on, the t-stat has done its job and is merely waiting for the temperature to change.  All the t-stat does is signal the furnace or a/c that there is a demand for heating or cooling.  Everything else is up top the unit that received the signal.
 
I didn't make myself clear.  There is a separate fan switch and the Fan works when it is turned on.

With the Fan Switch turned off and the Cool/Furnace switch set in Cool the A/C will not come on even with the Temperature Slide set to the lowest setting (no matter how long you wait).  With the Coll/Furnace switch set to Furnace the Furnace will not come on even with the Temperature Slide set to the highest setting.

Have done no checking but it sounds like there is no control voltage coming from the Temperature Sensor.  Will pop the cover off tomorrow and take some measurements to isolate. 

Will let you know what I find. 
 
Yeap. The "call for heat/cooling" signal is a simple +12v on the line to the furnace or a/c.  If the furnace or a/c fans don't start, that's an almost sure sign they they are not seeing the +12 voltage from the t-stat. Since neither furnace or a/c fans run when in heat or cool mode, that pretty well rules out a problem at that end, so it's most likely the t-stat wiring or possible the tstat itself. You could try jumping +12v to the wire to the furnace or a/c to determine which it is.
 
I appreciate your input.

It ended up being a broken wire from the Tstat to the A/C.  It was the Red Wire providing 7.5vdc from the A/C to the Tstat,  Coachmen used house type Tstat wires (#18 solid 6 conductor cable).  The cable was crimped at the A/C end.  There was sufficient wire length from the A/C leads so I didn't have to run a new Tstat cable. 

I do not understand why they run solid conductor wire in an RV that is subject to vibration.  Two additional wires broke at the Tstat end when I checked the connections, fortunately there was sufficient excess cable to cut and rewire. 

Again thks for the help.
 
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