We have a Lennox G12 series gas furnace, up-flow configuration. The blower access panel is no longer staying closed the burner access panel closes normally.

SOURCE: Sears 92 gas furnace noise when not in air handling mode

a very subtle hum or buzz is normal and is the transformer that creates 24 volt control voltage continually. some are noisier than others . sometimes a tap or bending of the transformer will tweak the metal enough to make it quieter. they can also get loud if incoming voltage is not correct. incoming 120 volts on a furnace is not usually a problem but the transformers are usually wired to the available incoming 230 voltage or 208 voltage if it is a heat pump or electric heat. If it is powered by 230 or 208 volts as most heat pumps are ,then you need to verify which you have and connect the appropriate leads from the trans former to power . it tells you on the side of the transformer which to connect to 230 and which to connect to 208. tape or cap off any unused leads.since you have not mentioned any performance problems i assume the fan does come on when called for and that it is not the loud hum you hear. switching the fan switch at stat to on should bring the fan on right away. if it doesn't then you may hear a loud hum and then youll need to check the fan motor and capacitor. but it sounds like a noisey transformer from here.

SOURCE: Heater no longer works on auto fan, only manual fan

When you call for fan in auto ensure your getting 24 volts at pin on control board, if it is not energizing then there is a problem with the relay.. Before you change out the expensive control board, try the therm..

SOURCE: Coleman presidential II furnace blower on and off

Sounds like the flame sensor. But it could be the thermostat. Is the furnace standing pilot or electronic spark or hot surface ignition. I would start by checking thermostat. Turn power off to furnace take thermostat off wall and take wires marked r & w and connect them together. Turn power back on if furnace works then change out thermostat.Most eclectronic ignition Furnaces have a flam sensor, You could take flame sensor out and clean it up with steel wool or wire brush. If you need anymore help just reply back .

SOURCE: Access to burner on Frigidaire Affinity AGQ6000 series dryer

you do have to pull out the unit and use the rear access to unscrew those screws accessable from the inside.

SOURCE: Rheem gas furnace blower unit not working properly

look at circuit board and follow wires that come from fan motor, if this is a standard motor black is high and it will be going to a prong that says cool, red is low and it will go to heat, you will have a yellow and a blue that are "parked" remove red park it were the blue is and put blue on heat, if this is a variable speed motor you will have to set dip switches via your equipment manual