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I'm sorry to hear about your issues with your furnace. When the furnace shuts down, what LED flash code do you get?
Also, can I get full model number? Lennox made two furnaces beginning with G40, the G40UH and the G40 DF.
OK, if it's blowing cold air, there will be a flash code in the small window in bottom of the furnace. I need that code.
It will not be seen in the top panel. It's in the bottom panel viewed through a small window. The code appears with furnace on, correct.
OK, now I need you to count the number of green flashes followed by a pause and the number of red flashes followed by a pause.
If they are both flashing simultaneously at a fast rate, that's a call for heat. Is the inducer motor at the top of the furnace running?
How many green flashes followed by a pause?
That means that the prove switch (pressure switch) was not made. Check for blocked vent or inducer not running. Also, pinched pressure switch hose or bad pressure switch.
First off: Is the inducer motor running?
The inducer motor can be seen in Figure 1, page 14 of this manual.
Called combustion air inducer in the diagram.
In that same diagram, they show a combustion air prove switch. It is round with a hose attached. Take the hose off, not on the prove switch end, but the other point it attaches and gently suck, then blow through the hose a few times.
When you're done, put hose back on and try again.
Look for a small round part with a rubber hose attached.
Probably black in color and hose may be black, too.
Yes, now need you to:
Take the hose off, not on the prove switch end, but the other point it attaches and gently suck, then blow through the hose a few times.
Nope, as I said, not on the prove switch end, but the other end. If you want, turn furnace off first.
The prove switch is the small black round part.
Yes. Leave the hose on that part, but take the other end off and gently suck then blow through the hose a few times. We are trying to "break free" the pressure or prove switch.
Nope, wont' do any good if you take the other end off.
If it's too short, you may need to go up to a hardware store and pick up a longer length of hose to perform this task.
If this doesn't work and inducer is running, the prove switch may be bad and would need replacement.
We are trying to do something that will prevent you from having to buy a part and has worked for me many times.
If you need to perform this and get back to me later, that's fine. Sometimes the hose is hard to get off on the other end because it gets "welded on" due to the heat.
Why don't you go ahead and work on doing this, then post back when you get done. Otherwise, as I said, prove switch may be bad.
Suck, then blow a few times. Gently. Then as I said previously, when you're done, replace hose, reset furnace (power off, then back on) and see if it starts.
Red LED off, green flashing slowly?
OK, more than likely this prove switch will need replacement. We tried anyways.
Yup. But at least now you have a better idea of what's going on.
One other thing you can try: on the other end of the tubing on the inducer assembly, where pressure switch hose attaches, there is a small barb that hose pushes onto. Take a small drill bit and push in and ream this out, make sure its clear. Occasionally this will plug up with rust, debris. I'm not saying this will work, but worth a try.
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