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ElCheapo · Dec 7, 2008, 02:06 AM

I went to finally turn on the heat for the first time and while it took a minute or 2 for the vent motor and burners to ignite, the main fan never started up. The fan does work with the AC, but does not work when I switch the fan to "on" at the thermostat. Could it be the integrated Furnace Control board? It seems odd to me that the fan would only work with the AC and not when the themostat switch was set to fan "on."
Thanks

hvac1000 · Dec 7, 2008, 06:24 AM

I have no idea what brand or model of system you have but it could be something called a fan and limit control or a relay. The relay may be contained on the furnace control board.

KC13 · Dec 7, 2008, 09:11 AM

Most furnaces equipped with an electronic control board activate the same blower speed for heating and continuous fan. If the cooling speed works, the problem is likely in the circuit board (relay) or wiring to the motor.

letmetellu · Dec 7, 2008, 10:29 AM

Originally Posted by ElCheapo

It seems odd to me that the fan would only work with the AC and not when the themostat switch was set to fan "on."
Thanks

From the part of your question above I can't help but think it is either the fan relay on the circuit board, or something in the thermostat.

I feel sure that your furnace runs on a different speed for heating than it does cooling, so I think that you have two fan relays on the board. In fact I think most are marked Heat or Cool. While your burners are burning and you ar waiting for the fan to come on tap the heat relay several times with the plastic end of a screw driver, If you hear the motor jump like it tried to start then I feel sure that your relay is bad, Some boards have plug in relays others are hard wired in place. So good luck, I hope you find the problem

ElCheapo · Dec 7, 2008, 10:49 AM

New issue this morning. BTW, thanks for the help so far. The burners finally stopped igniting, which maybe is a good thing, and the diagnostic LED is flashing 4 times (White-Rogers D341122P01... replacement board cnt 2789 or 2183) which indicates the "open high limit device" and I think I have traced that back to not being part of the IFC. My theory... if there is any problem with the board circuitry, it should eventually tell the rest of the unit (TRANE furnace) not to ignite the burners... ie... we have a board issue and before you blow the roof off your house, get the board changed.
Bottom line is that I do not want to pay some HVAC co. $500 for a $99 part. Thanks for your help!

KC13 · Dec 7, 2008, 12:59 PM

If the blower does not run during a heating cycle, the high-limit will eventually open and produce the fault code you are now getting. This "new" code is a secondary product of the blower not operating when it should, and will probably go away when the furnace cools down a bit.

ElCheapo · Dec 7, 2008, 01:07 PM

You're right KC, cooled down and back to normal... well, normal with no fan function. Removed the IFC board and there are a couple of black areas I suspect are bad. Once I replace the board in the next few days, I'll just report back the results. I suspect this will solve the problem and hopefully help someone else with similar problems. Appreciate the help!
Thanks

KC13 · Dec 7, 2008, 01:11 PM

Congrats, you have found the problem. If you are confident enough in your skills, there are ways to wire the blower directly to the power supply for interim heating. It will run continuously but allow the system to cycle normally otherwise. It sounds as if the IFC is functioning normally otherwise.

ElCheapo · Dec 7, 2008, 01:16 PM

Originally Posted by KC13

Congrats, you have found the problem. If you are confident enough in your skills, there are ways to wire the blower directly to the power supply for interim heating. It will run continuously but allow the system to cycle normally otherwise. It sounds as if the IFC is functioning normally otherwise.

I think I could handle this... if someone told me how. Is this as easy 2 line answer or more complicated? Otherwise we'll live (wife will suffer) for a couple more days.
Thanks

KC13 · Dec 7, 2008, 01:28 PM

Find the bank of terminals on the IFC where the blower leads connect. You may find that there are designations like cool, heat, and dummy terminals for unused blower leads-usually labeled "park". The wire connected to the "heat" terminal will have to be connected to the incoming power supply at some point. Terminal doublers work great for this, as you can remove the L1 wire from the IFC, put on a doubler, then reconnect the L1 and blower lead at the same point. It would also be a good idea to remove and insulate the wire connected to cool at the IFC to prevent damage to motor if the t-stat is accidentally set to cool.

njgg · Feb 15, 2009, 03:41 PM

Have you fixed your furnace problem? I have the same problem - burnt board cnt 2789. Plan to replace it with cnt03797 but not sure if that all worked out for you. Thanks for your help in advance!

Originally Posted by ElCheapo

New issue this morning. BTW, thanks for the help so far. The burners finally stopped igniting, which maybe is a good thing, and the diagnostic LED is flashing 4 times (White-Rogers D341122P01...replacement board cnt 2789 or 2183) which indicates the "open high limit device" and I think I have traced that back to not being part of the IFC. My theory...if there is any problem with the board circuitry, it should eventually tell the rest of the unit (TRANE furnace) not to ignite the burners...ie...we have a board issue and before you blow the roof off your house, get the board changed.
Bottom line is that I do not want to pay some HVAC co. $500 for a $99 part. Thanks for your help!