Good day, sorry for the delay, I was away at the cottage for the long weekend.
You are correct about the controls. The thermostat gets its power from the high or half heat part of the dial. Full heat supplies power to the thermostat and applies ground to a mauve wire in the harness, this activates the combustion air solenoid to open, and the fuel pump to stay pulsing fast.The half heat position may not even work, having been overridden-it tends to carbon up the heater, so high is best anyways. The vent position just blows cold air.
The starting sequence is
1- glow plug/spark and fan turn on right away
2- fuel pump starts at 25 seconds
3- if the flame sensor senses adequate temperature then the glow plug shuts off at about 1 min. and 15-30 seconds. and the heater continues to run-when it thermostats of or is turned off, the flame sensor should let it cool down for at least a minute and a half.
4- if the flame sensor does not sense adequate temperature by the 3 min. mark, then the heater will stop- if the heater does fire and gets hot, but it still shuts down at the 3 minute mark, then the flame sensor is bad- can't get them anymore either part # 25 1425 35 00 00
The reset button beside the glow plug is an OVERHEAT RESET BREAKER, not a heater coil reset. If it pops, it open circuits the fuel pump signal, and the flame goes out and the flame sensor then sends the unit in to cooldown. If the reset button does not click then it is not popped.
I would assume that the furnace will stop running 3 mins. after you turn it on in heat mode. If the glow plug is heating then it is in start mode and the fuel pump should have started to pulse after 25 second from being switched on. If it is not then it is one of the following-
-there is a pulse getting to the fuel pump, but it is stuck(it is a solenoid, and they sometimes get stuck) take the wires off the pump and turn the heater on- put a test light between the two wires, if it flashes then you have a signal and the pump must be stuck- whack it with the handle of a screwdriver. this will sometimes free it up,either permanently or temporarily. If the pump cannot be freed up, then it needs to be replaced, they are not available from Espar anymore. part number is 25 1425 45 00 00
- A tripped overheat breaker- not from what you say though
- A bad pulse generator- the smaller of the two aluminum control boxes behind the large rectangular face plate.this module generates a pulse from the from a signal sent to it by the motor brushes. If it is bad, sometimes you can make it work temporarily by putting a fairly strong magnet up against it after the 25 second mark- the magnet may activate the electromagnetic coil inside that the fuel pulse travels through- if this does make it work then the pulse generator is bad . Still available part # 25 1470 53 00 00 or 25 1470 54 00 00
- the motor brushes, or commutator in the motor may be worn too far- you can test this by tapping the motor shaft tip in the center of the orange fan impeller(fan) at the intake end of the furnace- do this with the furnace running-and at the 25 second after starting point-!!!!!BUT BE CAREFUL NOT TO GET YOUR TAPPING INSTRUMENT CAUGHT IN THE FAN WHEEL!!!!!!! it will fly off at a hundred miles an hour and kill you or at the very least punch a hole in the drywall or break a window. If the brushes, or commutator are the problem, then the fuel pump will start pulsing temporarily- Do this at your own risk!!
The motor is not available from Espar anymore- the part # is 25 1425 15 01 00
The motor can be re-brushed by an electric motor service company.
By the way the troubleshooting manual is at
http://www.espar.com/www/espar.com/help/
click on archive, then air heaters, then on D7L- you can then choose from parts, or TS(troubleshooting) pdf
Let me know if you are unsure of any of my explanations, or if you make any progress