hydroheat 7916 not working

[brdmh44]

Hi everyone, new to the forums. I just bought another truck camper last night, and plan to use it this weekend. After verifying proper operation of all lights, plumbing, electrical, and now appliances, my furnace does not work.

I've searched online and located a manual for the unit. It the sail switch is good, limit switch is good, gas solenoids are good, igniter is properly gapped and the board receives power. The fan activates, it never makes an igniter sound, and the gas solenoid only open for a second, if that. I'm pretty stumped as to the problem. I pulled the igniter and let it hang to the side to see if it did anything, and it doesn't. I suspect the igniter does not activate until the solenoid opens? I purged the air by lighting the stove and fridge, it has gas to the solenoid on a freshly filled tank. Local dealer recommended a new unit, but this seems like a simple thing I'm over looking. Any help would be much appreciated. Thanks all!

[Old-Biscuit]

This is generic description of RV furnace operation and applies to most DSI type furnaces.
1. The Thermostat calls for heat, sending DC current to the furnace.
2. A Time Delay Relay is energized and passes battery DC power to the blower motor.
3. The blower motor and fans spin, pulling air from the Air Return and generating a stream of air through the Heat Exchanger and out the Ducts. At the same time another fan pulls air from the Combustion Air Intake into the Combustion Chamber and out the Exhaust.
4. The fan air stream causes the Sail switch to close as the blower gets near full speed.
5. Power flows to the High Limit Switch and onward to the Control Circuit Board.
6. The Control Circuit Board opens the gas valve and generates a spark at the DSI Igniter.
7. The Burner ignites, building heat in the Combustion Chamber.
8. Heat passes through the Heat Exchanger, warming the air circulating through the Ducts.
9. The Thermostat reaches the Set Temperature and opens.
10. Power is removed from the Control Board and the Burner shuts down.
11. The fan continues to run to cool the furnace, until the Time Delay Relay opens again.

Step 6 is where you are having issues.......DC voltage is sent to gas solenoid and at same time to spark electrode. Voltage is applied to gas solenoids for only roughly 6-7 seconds total....if main flame doesn't light off and send signal back to circuit board (via spark electrode/sensor) the voltage to gas solenoid is cancelled.

Getting voltage to gas valve but no spark....
Bad spark electrode, bad high tension wire to electrode, bad high tension wire connection at circuit board OR back circuit board ignition track

[brdmh44]

The valves are commanded sometimes, but most of the time not. I believe it's I'm the board for that reason. The valves passed the test, but when they are commanded on or actually get power from the board, it's less than a second...

[Gripnriprod]

Can you use a butane lighter and get the pilot to light? Checks the gas valves unless the board doesn't send the demand.

[brdmh44]

Airflow is good, physically watched switch sail, and it supplied power to the board once the fans were up to speed. I'm just not getting anything to the igniter and it seems like a board issue. We will swap the board for diagnostic purposes and go from there. According to the diagram, all is well in there. I've literally dissected this furnace all day verifying power, grounds, continuity, and resistance checks. Everything points to the board now. I'm hoping this solves it. Otherwise I'm using an electric heater for the weekend, then installing the tune up kit and go from there. Previous owner said it worked for him. Google has netted me more than enough results regarding board failure so I'll see what happens.

[Gripnriprod]

Even if the sail switch is good it still has to "sail" Are you getting adequate air flow? Batteries are in good shape so the fan turns at the right speed? No obstructions in air intake or outlet, clogged filters, nests, etc?
It sure sounds like the sequence is stalling at the air flow established? step.

[brdmh44]

Thanks for the link Bob, I checked over everything they talked about and still nothing. My friend is letting me borrow his circuit board to verify mine is good. I hope that's it, at least finding a failed part wood be a start lol!

Thanks again, Bob

Brad

[bobndot]

I have this info if it helps.

http://www.popupportal.com/index.php?topic=32560.0

Bob

p.s. it could have an on/off switch , hidden where its hard to see it . That happened to me once.