Furnace main blower works ok on 110V and Genny but not 12V

[biggrock1]

Sent: 12/13/2003 7:08 PM

Hello again everybody.The blower or fan works fine all the time and the pilot stays lit
but the but the main burner will only stay lit with shore power or the genny running.I have the switch on the wall inside the furnace compartment set to 12 volt but as soon as I stop the genny , out goes the fire except for the pilot.

[DaveVA78Chieftain]

Sent: 12/13/2003 10:07 PM

When you remove the 110VAC source to the converter (shore power/genny), the system automatically switches over to the battery.  Sounds like the battery voltage is too low.  This results in the the blower motor not turning fast enough for the sail switch to make closure.  Start the engine to get the altenator working and see if it is ok that way when the shore power/genny is off.  Based on your description it should work ok with the altenator running.  You could even use a battery charger to act like the altenator if you want.  No electronics to worry about with a pilot model.
Do you have a electric heater running?  They can draw enough AC current when on shore power/genny that it draws the voltage down on the converter (resilts in low DC output).  If converter output gets to low, the blower motor does not turn fast enough to make the sail switch close.  I have had that happen to mine over the past week.  Part of my problem also though was that dirt had built up on the blower fan causing an imbalance (slows the motor down and makes it noisy).  The imbalance combined with the reduced voltage from the electric heater resulted in the fan running to slow.  Had to tear the furnance down today and clean the blower wheels.

Getting my furnance up and working correctly has been a real pain.  One thing that has been of great value though is I have added 3 status lights.  One tells me when the thermostat is on.  One tells me that voltage is getting to the DSI board (sail and thermal shutdown sensor are ok).  The 3rd one tells me that the gas valve is on.  For that one though, I connected it to the normally closed circuit on the DSI board.  When on, the gas valve is off.  When light is off, the relay on the board is energized sending voltage to the gas valve (resuls in the light going off).  That last one lets me know if the unit fails to light.  This way only 2 of the lights should be on.  3rd one on (after initial 20 sec start up delay to clear any residual propane in burner) tells me theres a problem.  For a pilot model, you could have thermostat on, sail switch ok lights.  Sure helps when trying to figure out what the unit is doing.  Unfortunantly, you cannot monitor the thermociuple on a piolt model.  Still 2 is better than none.  I just used 12VDC minilights from radio shack and 4 wire telephone cable (ground, thermostat, DSI board power, and NC DSI board contact).  to wire it all up.
I am now having to work out a gas delivery problem at the moment.  Acts like the gas orfice is not far enough into the burner tube such that it is burning at the orfice rather than along the tube (due to increased fan speed?).  Man, seems like I am learning everything you never wanted to know about a furnace!  LOL  Ahh well, maybe passing it all on will save someone else a whole lot of headaches.

Good luck - Dave

[biggrock1]

Sent: 12/14/2003 1:37 PM

I should also add that the electric ignition does not get hot enough to light the pilot

I also have 2 new Trojan 6 volt batteries that I will install this afternoon. If everything is OK, then I will look at my alternator.

[biggrock1]

Sent: 12/15/2003 2:40 PM

If you can't see what it's doing, it's very difficult to figure out whats wrong, ergo the monitor lights.  I did work out my furnance problem last night though.  Silly me had installed the small blower fan (burner chamber fan) on backwards.  Was not enough airflow for it to work right.  All happy now!  Well almost at least.  Will have to replace the DSI board before to long.  Bad solder connection on it that I have not been able to find/repair.  There is some sort of plastic coating on the board that makes it almost impossible to work on.  Discovered that if I flexed the board it would work.  So, for the moment at least.  It's installed so that it's flexed.  Works for now, will replace later.  To many other little details to get worked out for the moment.

Dave

[biggrock1]

Sent: 12/16/2003 2:50 PM

I installed the 2 new 6 volts and every thing is fine. My old  trailer batt. was defective. You guys are a wealth of information.
Thanks again