Main blower constant run with t- stat off and auto/fan switch in auto position. Unit not trying not trying to fire....draft inducer, ingnitor not coming on. Pulled ingnitor, appears to be good, pulled flame sensor and sanded it a bit, no change. fault code on board is 4 blips. I'm assuming bad draft inducer since thats the first step in getting heat but the 4 blips is kinda throwing me....so I look to the gurus for a little direction.
If it is calling for heat the draft inducer it is the first device energized, the pressure switch will want to be proved and then the ignitor will glow and the gas valve will energize and the sensor will prove the flame and the heat is on.
If one of the above is not in the right time and place the rest will not work. About the fan it is either a shorted control wire for the fan or the limit switch (the high temperature limit) is made or bad.
If that is not the case the the thermostat has a switch in the back between the gas fired or electric. That will determine if the fan should be on every call for heat.
He said he found the high limit,(dimes stacked) with an incomplete path, thus open, as you know the limit, is a Normally closed, N/C switch that opens on the rise of temperature. So the issue is the limit, I agree with your sequence of operation etc, but I have found that what makes the last 10-20% of being accurate is listening but knowing when to ignore as well, as it is just as easy to be thrown off by what you are told as well, in fact the diagnostics of most persons who call me are way off! lol!
I saw this after i reposted having thought this was lost, I apologize for the double posting.
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used an ohm meter today to test limit switch and roll out sensor, they both show a complete path through each. Used it to test the circuit side of vacuum switch and that of course showed an incomplete circuit. I pulled out what I think is the high limit switch...it is a 7" piece of plastic and on the end of that is a sensor about the size of 8 or 9 dimes stacked on top of each other. The whole arm is inserted into the interior of the furnace and secured with two screws from the exterior. I put the ohm meter on that and that shows an incomplete path. Is this the culprit for my concern. Also when I install it into the furnace does the sensor need to face up or down? I'm an idiot and forgot to pay attention when I removed it duuuhhh ;)
The answer is in the answer as is so often the case,....
. I put the ohm meter on that and that shows an incomplete path. Is this the culprit for my concern. Also when I install it into the furnace does the sensor need to face up or down?
As we all know a high limit is a Normally Closed switch,N/C, That opens on the rise of temperature, thus the incomplete path is not normal , the limit is open.
By the way, the middle statement was my repeating the ops statement in part.
r. I put the ohm meter on that and that shows an incomplete path. Is this the culprit for my concern. Also when I install it into the furnace does the sensor need to face up or down?
I put the ohm meter on that and that shows an incomplete path
A limits supposed to be normally closed , open on the rise
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