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Old 11-06-2011, 05:27 PM   #1
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Bad control board?


My draft inducer will not come on but the blower does. I checked the voltage from the control board to the inducer and its showing 77 volts and not 124 like my other furnace is showing. I also am not getting any readings on the W and R thermostat wires when calling for heat but I am showing 24 volts coming from the transformer back to the control board. I'm sort of a newbie to this and I just didn't want to have the control board replaced if something else could be causing it. Any ideas why I'm not getting any readings on the thermostat wires? I replaced my thermostat so I know it's good.

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Old 11-06-2011, 05:44 PM   #2
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Bad control board?


The inducer requires 115 volts. If you hard wire the inducer, taking the main furnace power wires and wiring them straight to the inducer (you need to comfirm that you're receiving 120-ish volts through those main wires first because if you're entire furnace is only getting 77 volts than you have an electrical problem) and turn the power on. On call for cool you can pull the blower wire off of the cool terminal on board and check voltage there. It should be 120-ish as well. Your inducer has nothing to do with cool so while on call for cool you should have a full 120-ish volts on cool terminal. If 77 volts only then again, electrical problem to furnace such as a loose neutral or breaker going out.

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Old 11-06-2011, 05:45 PM   #3
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Bad control board?


first thing is if the furnace is powered up on the servcie switch on the side.....the transformer is always sending 24vs to the board even if the sta is off the wall....the stat controls the board thru that R to W...so remove the stat from the subbase remover R/W wires and JUMP IT OUT put the wires together... up in the house.now you have a straight heat no temperature control...down at the furnace with that jump the Induced Draft should be the first thing to run concentrate on the 77Vs the board is supplying it.... check the 115V to ground for the motor out of the board trace the wire to it 115V maybe the motor neutral is loose.if you want get an extension cord remove the motor feed wires and plug it into the extension cord see if it runs..don't need to remove the motor keep it in place see if you get the furnace to cycle on.. testing the motor...before the jump remove the ID motor wires and read the terminals for 115v with the furnace calling...ring the motor winding OHM setting touch both wires from the motor should be a short...then each wire to the motor body no reading 0.00 no contact as in shorted...lets here backNOTE:don't swet the stat jump just work the service switch on the furnace for now to cycle.... prices on boards if you need one http://www.bestbuyheatingandaircondi...cuitboards.htm

Last edited by biggles; 11-06-2011 at 05:50 PM.
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Old 11-06-2011, 06:25 PM   #4
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Bad control board?


Well good news. I pulled out my circuit plug from the control board and when I plugged it back in the the inducer came on for a split second. I thought, hmm. So then I sort of pushed the plug up and bamm, it lit right up. I guess my plug wasn't making a good connection. Wished I tried that earlier. Thanks so much for the quick replies. This forum is great.
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Old 11-06-2011, 07:03 PM   #5
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Bad control board?


good never know what happens when your pushing those multi pinned boots in....cheap fix
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Old 11-06-2011, 07:50 PM   #6
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Bad control board?


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good never know what happens when your pushing those multi pinned boots in....cheap fix

This is the second inducer wire connection problem in as many days. Something to retain in the memory data bank.
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Old 12-24-2011, 08:12 AM   #7
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Bad control board?


Well I'm back again. So I continue to have connection problems. It seems like every 3 or 4 days I'd wake up and cold air was blowing out of the vents so I'd go wiggle the wire plug on the control board and the burners would fire up. This morning though it's not firing up. I wiggle the plug and it just sparks behind the control board but the burners never come on. The blower is still on though. As I mentioned last time I am only getting 77 volts to the inducer when this happens. One thing I noticed is I can wiggle the plug so the blower isn't running and when I do I get 124 volts to the inducer. Same thing for my red thermostat wire. When the blower is on no voltage but when it's not it's normal voltage for a call for heat. Also when I pull the plug completely out the blower still runs. That may be normal but I just wanted to mention that. So could it be something else I'm missing or is this just a bad board? Thanks.
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Old 12-24-2011, 08:35 AM   #8
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Bad control board?


In heating mode blowers have a time off delay. I'm not sure if this applies to when you pull the plug completely off though. After the desired set point in heating mode is reached via the stat, the burners cut off but the blower remains on for a short period.

Does the blower eventually stop or not? The delaly could be one minute, 120 seconds, 180 seconds, etc. so you need to let it run for that long to determine if it will shut off.
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Old 12-24-2011, 09:20 AM   #9
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Bad control board?


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Well I'm back again. So I continue to have connection problems. It seems like every 3 or 4 days I'd wake up and cold air was blowing out of the vents so I'd go wiggle the wire plug on the control board and the burners would fire up. This morning though it's not firing up. I wiggle the plug and it just sparks behind the control board but the burners never come on. The blower is still on though. As I mentioned last time I am only getting 77 volts to the inducer when this happens. One thing I noticed is I can wiggle the plug so the blower isn't running and when I do I get 124 volts to the inducer. Same thing for my red thermostat wire. When the blower is on no voltage but when it's not it's normal voltage for a call for heat. Also when I pull the plug completely out the blower still runs. That may be normal but I just wanted to mention that. So could it be something else I'm missing or is this just a bad board? Thanks.

You never said what type of furnace this is.......is it a carrier, possibly 1995 era ?
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Old 12-24-2011, 09:35 AM   #10
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Bad control board?


the plug you pull has the pins in it make sure they are lined up to marry up into the board female...if you can trace the ID wires thru the plug onto the board then remove the male in hand restart the furnace and read the female off the board to see if the board is actually sending the 120V for the ID.....loose connections especially boots male/female will give false readings....vibrations from the fan could be just enought to knock the 120V to 77V on the ID during heat....remover the board off the screw mounts slip a piece of cardboard under it....take a thin piece of wire and or jumper and go from the screw hole on the board to a unit screw just incase the board needs a grounding now that it's floating.on those male pins they might have splits on there tips might spread them ever so slightly...with a razor or pocket screw driver...
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Old 12-24-2011, 09:35 AM   #11
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Bad control board?


When the plugs are disconnected the board sees it as an open limit and runs the blower. That part is normal.
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Old 12-24-2011, 09:57 AM   #12
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Bad control board?


Yeah it's Carrier...installed when the house was built in '93. I didn't want to pull the whole board off yet because I'd have to pull out a lot of wires to get it off. It's still confusing me why when the blower runs the voltage is low to the inducer but when I move the plug to cause the blower to stop the voltage to the inducer is normal. I've got a local tech that does $25 service calls so I may just get him out.
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Old 12-24-2011, 09:59 AM   #13
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Bad control board?


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Yeah it's Carrier...installed when the house was built in '93. I didn't want to pull the whole board off yet because I'd have to pull out a lot of wires to get it off. It's still confusing me why when the blower runs the voltage is low to the inducer but when I move the plug to cause the blower to stop the voltage to the inducer is normal. I've got a local tech that does $25 service calls so I may just get him out.
the original c/b had a recall on it due to bad resistors that came lose from the soldier joints...........sounds like classic case of "this one slipped through the cracks"........not a cheap board either.

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