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I have no voltage to my thermostat - Dometic Rooftop RV Air Conditioner

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Hi, I am not positive the control voltage to your thermostat will be on a RV a/c, most homes are 24 volts. I know yours would be less. If you have a 2-wire stat and this a/c is not working, take the two thermostat wires a touch and hold them together. Don't worry as this is safe and will not shock you. If the unit comes on and runs, you do have voltage there but the meter may be set wrong. If nothing happens, then you need to find the breaker for this unit to see if it as tripped. Reset it anyway. If still no power, you will need to find the transformer for this unit and check for power to it which will be high voltage/primary and power out which is the secondary low voltage which controls all low voltage controls such as the stat. If you have a wiring diagram on the condenser up top or most RV have a large book that tells you about your coache. If you have a diagram look for the thermostat as it will be labeled in the legend as a T with a circle around it or it may say stat. Follow to see where it gos from there, to the transformer or what and let me know. If the unit does fire when you jump out the stat wires, you will have to replace the stat. Please keep me posted on this. You may have a blown fuse up top cutting off power to the transformer also. You can ohm them out also. Keep me posted so we can solve this.

Posted on May 13, 2010


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Short answer: Thermostats may be bad. Replace both thermostats.

Long answer:
1) If water heater has some hot water, then upper element is good and water heater has 240Volts, and best suspect is burned out lower element.

2) If water heater has no hot water because 240volt circuit breaker is tripped on one leg, and only 120Volts is arriving at water heater, then upper part of water heater can appear to have voltage and lower part of water heater can appear to have no voltage.
Open following links for troubleshoot steps:

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