Hello,

I have a Lennox Heating and Air unit. The furnace which is in the attic is model # G40UH-36A-070-11. The air conditioner outside is model #13acd-030-230-01. The AC fan does not come on. I turned on the heat to see if that would work but that wouldn't come on either. I can hear the themostat click when I set the temp above or below the temp that it is in the house so that seems to be working properly. I called an AC repair man who came out and told me that the problem was the control board because there was no power going to the A/C or the Furnace. I looked at the control board and saw that neither the green or the red LED lights came on. I ordered the part # 17W70 which I was told replaced #78M47 and installed it but the LED lights still didn't come on nor did I have any power to the AC unit outside or the Furnace. Does anyone have any suggestions to what the problem could be seeing as the circuits are not tripped and I've replaced the 24v control board?

I am having the same problem with my Lennox. I can here the unit outside buzzing when I ask for A\C but the fan won't turn. I know I have power both in the outside unit and furnace. I have read a few posts and the common denominator would be the fan capacitor in the heat pump.

Have you checked for 120v on primary of transformer and 24v at secondary of transformer. I would actually start by checking to make sure there is 120v to furnace. If there is, check for 24v to control board. This may be as simple as an inline fuse. Im hoping that the ac tech checked all of these things before saying it was a bad board, but if you replaced the board and wired it correctly, I have a hunch its something much simpler than the board. A lot of people will just quess that the baord is bad when they can't find any other problem, usually its because they don't know how to test for other problems. Please let me know if you have any power to the furnace. Remember, the blower door has a safety switch which much be pushed in to activate power to furnace.

If the board went bad than the transofer did too. 9 out of 10 times they go hand in hand. I am surprised a tech did not catch that.