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SOLVED! OFF TOPIC - Any HVAC Furnace experts here?? I need help!!

Caliguy

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Please help me. This has had me scratching my head for a week. Iv had a tech come out and they’re scratching their head and trying to throw parts at it.

It’s a carrier furnace model number :58MXB080-F-10116

So far, I have replace flame sensor, gas valve, capacitor, filter - no difference in any of the repairs.. arguably, got a little worse after the new gas valve as it would sometimes work for a day or so with the old gas valve, now we get consistent failures.

Here are the symptoms:

When unplugging or off for a long time, and turned on, the fan relay will click on and off several times and eventually the fan will start after about 10-15 clicks with the fan turning on for longer periods of time each time but usually not for more than a fraction of a second to 1 second.

If I go to the thermostat and turn to heat and fan on, I can eventually get the inducer motor to turn on first, then the coils will ignite, then the coils turn off, and the fan comes on.

After the fan is on for about 30 seconds, the fan relay clicks and the fan turns on and off for a second multiple times and will actually turn the fan on for 30 seconds then go back to on and off for a second. The cycle will continue until I turn off the thermostat.

If I turn on the thermostat again, the inducer motor will start, coils will ignite, and the cycle continues as above.

Seems as if the fan works, the inducer works, the gas valve works, the coils are working, but something isn’t working correctly to make it all work together except for the beginning of the cycle when I turn the thermostat on for the first time.

Here are some videos:

Initial startup after being unplugged or off for a long time:




Here is what happens when I turn on the thermostat:





Then, the coils turn off, the inducer motor turns off, and the fan turns on




Then the fan turns off, and you can hear the relay clicking to turn the fan on again




After a few attempts, the fan will turn on for about 30 seconds, then the cycle continues of attempting to turn the fan on again








Here is a full cycle:





Any help is appreciated. If someone can diagnose the correct fix, I’ll send them some $$$$!
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Beachcomber72

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Personally I’d bet it’s the actual thermostat on the wall. Chased the same crap down 7 years ago to finally find it as the culprit after 9 hours of multiple tech attempts. Sadly…
 

Beachcomber72

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Double check your air filters too for any that need to be changed out.
 

cornercanyon

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. . . realizing each day–
Personally I’d bet it’s the actual thermostat on the wall. Chased the same crap down 7 years ago to finally find it as the culprit after 9 hours of multiple tech attempts. Sadly…
You could pull the thermostat and hard (twist) wire the connection? We used to do that in the winter while trimming out houses—
 
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Caliguy

Caliguy

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Double check your air filters too for any that need to be changed out.
Filters changed out already, running to Home Depot now for a new thermostat. If this doesn’t work, it can only be the circuit board I think
 

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cornercanyon

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. . . realizing each day–
Wouldn’t a jumper cable do the same thing at the furnace?
I am not an electrician, even so without knowing what you are jumping I don't know. Easy to pull the thermostat off the wall and just twist some wire—
 
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Caliguy

Caliguy

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The fan has a high/low limit switch. Sensing no heat it shuts down and is probbly working correctly. No fire /flame, ignitor or fuel ?
Correct, it should be turning on inducer then coils then fan. For some reason it tries to turn on fan first. So it’s either the thermostat sending bad signal, or the pcb gone haywire it sounds like
 

Tgs

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There should be a light on the furnace. It will flash after a fault. The flashing is a fault code see if you can find what the fault is.
 

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mantronics

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20+ year HVAC tech here🛠. Hard to tell in videos. Sequence of operation is as follows….. thermostat calls for heat, inducer fan turns on, pressure switch opens confirming inducer motor is running and exhaust pipe is clear, ignitor glows, gas valve opens, flame sensor located in path of burners proves flame sensor has lit gas burners, circuit board fan relay turns on blower after factory set time( to allow heat to build up and blow vs a blast of cold air), heat stays on until stat is satisfied, burner turns off, blower fan stays on couple minutes longer to blow heated air out of ductwork…… the end😃.
 

mantronics

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The only thing that would cycle the fan like that would be a bad furnace circuit board fan relay. Sounds like a bad board.
 
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Caliguy

Caliguy

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The only thing that would cycle the fan like that would be a bad furnace circuit board fan relay. Sounds like a bad board.
Does jumping the board elongate a bad board?

Meaning a jumper wire from the R and W turning in the inducer or a jumper wire from R and G turning in the fan say the board is working correctly?
 

Beachcomber72

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The only thing that would cycle the fan like that would be a bad furnace circuit board fan relay. Sounds like a bad board.
I believe the fan relay can get caught in an odd loop as such but it still has to get an input start/stop cycle signal from the thermostat to energize the fan relay correctly. Otherwise it’s just considered a zombie electrical device.

great points from everyone here really, this situation reminds me why I’m thankful I have a dedicated furnace unlike our other house that had a heat pump system.
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