QuestionI have an NT-34S Surburban furnace that will not ignite. After diagnosing I discovered 13 volts going into the circuit board but only 7 volts coming out (to electrode and gas valve). Is this definitly a circuit board problem or possibly a ground problem? I have hot and neutral 12 volts connected. Does the unit itself act as a ground? Thanks
AnswerI cannot find a schematic for this one that I can download but I can tell you that most of these boards will reduce voltage for different functions, I have seen 1.5, 3, 5, 7, and 9 volts in different boards. I would check these first
The gas valve and solenoid assembly
High limit switch and sail switch
and orfice.
The ground is run through your ground line but it will also have a couple of grounds connected to the heater chassis. If you do replace the board you can get an aftermarket board which by all reports from techs and users alike is a better board, from http://www.dinosaurelectronics.com/
Below is a desc of basics for furnaces..
Basic Furnace Operation
Provided by Harold, the RV MD
The typical function of the ignition is as follows.
1. Points on thermostat close, calling for heat from the furnace.
2. Blower on furnace comes on supplying fresh air to the combustion chamber, and closing the sail switch to inform the ignition board that air is flowing.
3. After an delay to allow for purging of the combustion chamber, the spark igniter is started and the gas flow valve is opened.
4. If after approximately 7 seconds the burner hasn't lit the gas is shut off. Some igniter boards will retry a second and third time. Some only try once.
There is also a high temperature shut down in the furnace, however if it isn't closed the furnace will never ignite.
If I can get specifics on your model I will email you again.
