Furnace not blowing heat, troubleshooting blower vs control board

fomocolovesu

Furnace starts up without issue. Blower won't turn on. Tested capacitor and it is fine.

When the signal is sent to turn on the blower, I hear a "click" then nothing happens. I tested the leads on the control board between High Heat and Circ and didn't get a reading, so I thought the board might be bad. Tried to hot wire the blower by connecting the High Speed Heat wire to the line out from the kill switch. What is strange is that I head the same "click" and the blower does not turn on. However, the LED on the board starts blinking indicating that the control board has power. Thoughts? What am I doing wrong?

Thanks!

Ryan

fomocolovesu

PS, squirrel cage on blower spins fine and the motor itself is not hot, so it does not appear to be trying to turn on (which also leads me to believe there may be a control board issue)

HVACNUT

You should be taking the voltage reading between Hot (Heat) and Neutral, not circ.

The click means the relay is energized but doesn't necessarily mean the contacts closed.

If it's a multi speed motor you could try swapping to a different motor lead. That might be a temporary repair because the heat rise must still be within manufacturer specs.

fomocolovesu

Circ = Neutral on the board. I have two of the same units, when I do the same test on the other one I get 120 volts.

What is puzzling me most is would the board get power if I am taking the line in directly to the blower and circumventing the board?

JUGHNE

With everything back together, you could try the "fan on" switch on the tstat. If fan runs then motor is most likely OK.

If no fan switch then jumper R to G on low voltage board.
If good there then reverse cooling speed with heating speed to check that winding.

If motor passes tests then most likely the board.

fomocolovesu

What is the difference between Line H and Line N on the control board? I was trying to hotwire the blower to Line N and it wasn’t working. However, the blower works on Line H.

I’m confused because on my second unit, plugging the blower directly into Line N turns it on ...

fomocolovesu

Regardless, it appears the issue is with the board and not the blower!

HVACNUT

> @fomocolovesu said:
> Circ = Neutral on the board. I have two of the same units, when I do the same test on the other one I get 120 volts.
>
> What is puzzling me most is would the board get power if I am taking the line in directly to the blower and circumventing the board?


Circ is NOT Neutral. Circ is circ. As in "Constant Circulation". It is a 120v HOT terminal.

And from reading your 12:04 post, putting the blower lead on "Line N", which is Neutral means you're not troubleshooting correctly.

How did you test the capacitor? What is its rating and what was the reading?

fomocolovesu

Unfortunately my meter doesn't measure MFD. It passed the ohm test though so I plugged it into my other HVAC and it works fine.

That said, I was able to run the blower directly by circumventing the board (you are right, I was connecting incorrectly before). Going to try and replace the board and see how it goes.

Thanks for your help.

HVACNUT

There you go.
Keep the blower running constantly for now and the burner will cycle as needed with a heat demand.

Better yet, did you try what @JUGHNE mentioned and put the thermostat to "fan on" if it's a heat/cool thermostat. In some boards the G terminal powers a different relay.
Or jump R to G on the board.