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Old 11-29-2010, 09:45 PM   #16
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Lennox furnace shutting down before desired temp reached


The blower does not make any unusual noise when starting up. The blower circuit board has model # 65K29. There is 120 to both the L1 (black) and neutral bar (white). There is a red wire attached at the H. getting 0.00 at this. All readings taken after limit switch tripped.

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Old 11-29-2010, 09:50 PM   #17
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Lennox furnace shutting down before desired temp reached


Readings of 120 white, 120 black and 166.6 at orange while blower is running.
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Old 11-29-2010, 10:04 PM   #18
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Lennox furnace shutting down before desired temp reached


white is common, black is high, red is low, orange and or blue would be interim between high and low.....red is typically used for heating

Blower Speed Taps
Blower speed tap changes are made on the BCC blower control board at the upper right corner. Unused speed taps must be secured to the dummy "D" terminals on the BCC. The active heating tap is connected to the "H" terminal and the active cooling tap is connected to the "A" terminal. To change a heating speed tap, turn off power, remove existing speed tap from the "H" terminal and place on "D" terminal. Next select new speed wire and place on "H" terminal of the blower control and restore power.
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Old 11-29-2010, 10:30 PM   #19
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Lennox furnace shutting down before desired temp reached


Sorry, think you lost me on that. The H terminal has a RED wire, the ACC terminal has a BROWN wire, the XFMR has Black as do the CAB, L1 and A terminals, White to all Neutrals. NO wires to any of the 3 D terminals or the CF.

It was actually the RED wire that read 166.6 when blower running and 0.00 when switch was tripped.

Not sure what you mean by unused speed taps or new speed wires. All wires are connected.

Thanks for the patience and answers.
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Old 11-29-2010, 10:44 PM   #20
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Lennox furnace shutting down before desired temp reached


move the wire on a to h and h to a and restart unit and see if it trips, this will be increasing your blower speed
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Old 11-29-2010, 10:51 PM   #21
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Lennox furnace shutting down before desired temp reached


Thanks, I'll try that. Shutting off all power first.
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Old 11-30-2010, 12:22 AM   #22
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Lennox furnace shutting down before desired temp reached


Didn't seem to make a difference, but thanks for trying. Still only will raise temp a couple of degrees before limit switch triggers. Also only runs blower while thermostat fan is in ON position, no longer works in AUTO. (Just started this) Guessing the blower circuit board needs to be replaced. Unless someone has another suggestion?
Our old furnace ran for 20 plus years with no problems, bought the Lennox on advice of an HVAC installer. Have replaced ignition control module, fan & motor, and now the blower circuit control board in 10 years. Won't be replacing with another Lennox!! What brand has the least problems / is most reliable and efficient?
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Old 11-30-2010, 12:28 AM   #23
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Lennox furnace shutting down before desired temp reached


no, that does seem to be the problem.... the new lennox number is 48k98........ its a lennox universal single stage board to replace all their single stage boards it comes with stuff you wont need, but this is how they are offering it now
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Old 12-04-2010, 10:33 PM   #24
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Lennox furnace shutting down before desired temp reached


Replaced the burner circuit board. ($98 on Amazon) Works great. The old one had a big burn spot on the back. Thanks for all the help. Third time I've been able to fix by myself with help on this and other sites. Still thinking when it finally goes I won't buy another Lennox though.
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Old 10-12-2012, 08:42 PM   #25
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Lennox furnace shutting down before desired temp reached


I have the same furnace and am having the same problems. Before I buy a replacement board on Amazon, I was hoping to confirm with you all that we have the same problem.

The furnace will turn on and will flame for about 30 seconds to a minute then shut off. Reading the instruction manual, we went through the checks and it appears to be a bad bcc as there is no voltage between N1 and A (I made an assumption that N1 is the first neutral terminal). I also checked the reading on the brown rectangle with two wires that was 24V leading us to believe that it was over heating. Could there be any other issue that we're not thinking of? The blower motor and capacitor were replaced two years ago so hoping that isn't a problem again.

Thanks!
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Old 10-12-2012, 08:58 PM   #26
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Lennox furnace shutting down before desired temp reached


Quote:
Originally Posted by griztown View Post
I have the same furnace and am having the same problems. Before I buy a replacement board on Amazon, I was hoping to confirm with you all that we have the same problem.

The furnace will turn on and will flame for about 30 seconds to a minute then shut off. Reading the instruction manual, we went through the checks and it appears to be a bad bcc as there is no voltage between N1 and A (I made an assumption that N1 is the first neutral terminal). I also checked the reading on the brown rectangle with two wires that was 24V leading us to believe that it was over heating. Could there be any other issue that we're not thinking of? The blower motor and capacitor were replaced two years ago so hoping that isn't a problem again.

Thanks!
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