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Flashing LED counter for Furnace CFM

My Coleman furnace control board has a flashing LED that normally indicates CFM. The pattern flashes once per 100 CFM, and after a number of flashes, it pauses, comes on half bright, then goes off before repeating the counting pattern.

Problem is that it has stopped flashing, and only comes on steady now. I recently had to repair the ECM module on the blower motor. ($10 thermistor saved me $2000-$4000 by not replacing the blower motor or the whole furnace!)

Anyone know how the LED counting/flashing part of a furnace control board works? Where is the input data coming from, and where should I be looking to troubleshoot this?

Thanks, Ross

Ottawa, Canada

Reply to
ross.cowie
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Depends on what it is *actually* intended to indicate.

I.e., is it truly measuring flow rate? Or, just reporting "blower RPM's" and scaling that to represent theoretical CFM?

(Why does it even *bother* to report CFM??)

Reply to
Don Y

I guess the question would be, did it stop working after you made repairs?

What part of the circuit was the thermistor in ? Over temp control or was it part of a mass air flow sensor ?

Is this control board the same board that you repair which is part of the blower circuit?

Setting that aside. Maybe the LED did work for you some time afterwards, do you have a flapper in the pipe that has an actuator or some sort of position sensor on it to indicate air flow? If not for a mechanical type of mass air flow sensor, could you have a thermal mass air flow detector which is sits in the pipe as a probe ?

Tomany questions because you don't supply enough details about your system

I would think the system would shut down if it wasn't detecting air flow, to prevent over heat of the local fire box. Also, you should have an exhaust flow sensor, too.

Jamie

Reply to
Maynard A. Philbrook Jr.

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