ILIA Posted May 2, 2011 Share Posted May 2, 2011 I know we're halfway through spring, but I need everything functioning the way it should just in case. Randomly my furnace stopped working and I can't figure out what's wrong. Duo Therm 66100. Nothing is getting power except that I occasionally see a light flicker once. Strange because the igniter would click many times to ensure the gas got lit. Tried twisting the thermostat wires together since they showed 12.6 volts, but nothing. Is it possible that the fuse on the particle control board is blown? Any other tests you all recommend before I pull the control board? Quote Link to comment Share on other sites More sharing options...
waiter Posted May 2, 2011 Share Posted May 2, 2011 The symptoms you gave are confusing?? If you have 12 volts at the thermostat wire, your probably OK as far as power is concerned . On mine the sequence is: 1) Call for heat ((short the thermostat wires together) 2) short delay (3 - 5 seconds) 3) Blower turns on 4) 3 - 5 seconds later - Gas valve opens and igniter starts clicking. 5) Furnace runs (igniter turns off) ------- 6) When Thermostat opens (unshort the wires) 7) Gas valve turns off 8) after 15 - 20 seconds blower turns off. I don't remember what model I have, so it may differ from yours, but I believe the sequence would be similar. John Mc 88 Dolphin 4 Auto Quote Link to comment Share on other sites More sharing options...
ILIA Posted May 3, 2011 Author Share Posted May 3, 2011 Mine works the exact same way which makes me believe that since there's 12 volts at the thermostat, then there should be power going to the fan. Unfortunately the fan never kicks on to start the process. The wiring diagram shows a 3 amp fuse on the unit. Is it unlikely that it blew? Quote Link to comment Share on other sites More sharing options...
ILIA Posted May 3, 2011 Author Share Posted May 3, 2011 The thermostat without a doubt functions as it should, and there is 12 volt power going to the unit. Oddly after about 7 seconds after turning on the furnace I can hear a quiet click that sounds like the gas valve opening. So my question is what is in line to the fan motor? Is the 3 amp fuse on the unit a possible culprit, is there some type of faulty capacitor, or do you think the fan motor is bad/stuck? Thanks for trying to help. Any feedback is much appreciated. Quote Link to comment Share on other sites More sharing options...
Vanman Posted May 3, 2011 Share Posted May 3, 2011 The thermostat without a doubt functions as it should, and there is 12 volt power going to the unit. Oddly after about 7 seconds after turning on the furnace I can hear a quiet click that sounds like the gas valve opening. So my question is what is in line to the fan motor? Is the 3 amp fuse on the unit a possible culprit, is there some type of faulty capacitor, or do you think the fan motor is bad/stuck? Thanks for trying to help. Any feedback is much appreciated. [/quote From what I have read here making the thermostat contacts starts the blower, when the air pushes the vane to make the vane switch that allows the pilot igniter to start. Once the pilot is lit another switch makes allowing the gas valve to open. There are timers between all of these processes, which sounds to me just like the way a home forced air heater works. Somewhere here I found a more detailed description of the heaters in our rigs, check the older posts. vanman Found the PFD, the thermostat contact goes to a time delay relay, which turns on the motor, the air switch is called a sail switch which feeds a heater limit switch( over temperature) , which feeds the module board, which controls both the igniter and gas valve. This PDF does not show a fuse. I have had the cover off mine and do not remember seeing a fuse, but yours may be different. Quote Link to comment Share on other sites More sharing options...
waiter Posted May 3, 2011 Share Posted May 3, 2011 ILIA; Sounds like you got the sequence down correctly. The gas valve should NOT open unless the fan is running (safety feature) I wonder if the click you hear is the fan relay?? I don't remember any fuses on the unit, but that doesn't mean there aren't any there. Pull the front cover and take a photo, and post it up here. These things are fairly simple, I replaced the blower motor on mine (it was squealing). If you get to the point where you suspect it is the blower, you can use a couple jumper leads and try and run the blower directly off 12 Vdc. Here is a link to my blower motor replacement, Photos may help you http://toyotamotorhome.org/forums/index.php?showtopic=3520 John Mc 88 Dolphin 4 Auto Quote Link to comment Share on other sites More sharing options...
ILIA Posted May 6, 2011 Author Share Posted May 6, 2011 Well I pulled the unit out an hour ago and noticed a few strange things. I twisted the thermostat wires together earlier one more time to perform a few voltage checks and realized that the fan motor got very hot, but still wouldn't turn over. Went ahead and pulled the unit, gave the fan wires 12 volts and the fan kicked right over and ran smooth. So what's my problem? Is the fan not getting enough juice? I'm gonna do some research on my own, just wanted to post my progress first. Thanks for the help so far. Quote Link to comment Share on other sites More sharing options...
ILIA Posted May 6, 2011 Author Share Posted May 6, 2011 Looking at the wiring diagram and at the unit itself leads me to believe that the relay switch went bad. It looks like a small black cube with wires attached at all 4 sides. Any idea where I can find one? Quote Link to comment Share on other sites More sharing options...
ILIA Posted May 6, 2011 Author Share Posted May 6, 2011 And I'm still confused as to why the motor would get hot, but not run. Quote Link to comment Share on other sites More sharing options...
waiter Posted May 6, 2011 Share Posted May 6, 2011 The relay sounds like a standard automotive cube relay, any auto store should have one. Use your voltmeter and see how much voltage the fan has on it when its trying to run. If this goes through the relay, you could have bad contacts in the relay and not giving full voltage to the fan (This is a long shot - but as you say, if you connect the fan directly to 12 volts and it runs, then it should run!!!) Sounds like your making progress. John Mc 88 Dolphin 4 Auto Quote Link to comment Share on other sites More sharing options...
ILIA Posted May 7, 2011 Author Share Posted May 7, 2011 Relay at the local auto-parts store cost 6 bucks. The RV parts department wanted 20. Is there any difference? I thought not and installed the cheaper one assuming they preformed the same function. Reinstalled the furnace and everything is working as should, however. I didn't actually get the propane flowing yet because I'm waiting for the pipe sealant to cure overnight. Although, the fan works and I can here the sail switch click followed by the igniter so all looks good. Thanks for all the help. Quote Link to comment Share on other sites More sharing options...
waiter Posted May 7, 2011 Share Posted May 7, 2011 ILIA; EXCELLENT - Another satisfied customer :-) A nice thing about it, you not only have a furnace that works, but you probably know more about it than most service techs. :-) When I first start propane appliances after the bottle has been turned off, I usually lite the stove first just to purge most of the air out of the propane supply lines. JOhn Mc 88 DOlphin 4 Auto Quote Link to comment Share on other sites More sharing options...
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