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Old 12-05-2010, 01:36 AM   #1
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Bryant 340MAV - Control board just flashes


I have a Bryant 340MAV furnace with a United Technologies HK42FZ009 control board. When the thermostat calls for heat, the blower comes on, but the burner doesn't and there is no heat. The inducer motor never comes on. The LED on the unit flashes steadily, but the AC polarity is correct. The unit does not respond to a request to self-test. Jumping the test terminal to common just results in a relay clicking. There is no error code read out and the unit doesn't sequence through the component test.

Any ideas what's wrong? Any other test I should run?

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Old 12-05-2010, 08:30 AM   #2
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Bryant 340MAV - Control board just flashes


Probably a bad circuit board. Relays eventually stick and fail.

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Old 05-14-2011, 06:58 PM   #3
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Bryant 340MAV - Control board just flashes


Billd17,
A couple days ago i noticed that my furnace does not work. I have the same control board like yours HK42FZ009. When the thermostat calls for heat, the blower comes on, but the burner doesn't and there is no heat. The inducer motor never comes on. The LED on the unit flashes steadily. The unit does not respond to a request to self-test. Jumping the test terminal to common just results in a relay clicking. There is no error code read out and the unit doesn't sequence through the component test.
Have you diagnozed what was the problem with your Bryant 340 MAW. It seems that my furnace has the same problem.
Has anyone have any opinion what may be the problem. Control board or someting else.
Thanks
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Old 05-14-2011, 07:24 PM   #4
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Bryant 340MAV - Control board just flashes


Bad board, relay or tripped high limit switch. When a high temperature (excessive heat) limit switch trips the blower will come on as it is trying to push any heat out of it. The burners are cut off until that limit switch is reset or replaced as there is no point in producing more heat if there was excessive heat to begin with. That is how a furnace is wired, to not produce more heat and to try and blow out any heat that may be in there IF a high temp limit switch has tripped any time that furnace is turned on.

High limit switches trip because of restrictied air flow such as a blocked return air (filters) and/or a dirty and blocked evaporator coil.

Now if the high limit switch has tripped then more than likely there will be a flash code for this problem.
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