Lennox diplomat 80MGF blower works for heat but not a/c

[jcoleman71]

I have a Lennox Diplomat 80 MGF, went to turn on the A/C today and the blower never kicked on. I switched it back to heat and it worked as normal. I had the blower motor replaced last fall so I doubt that would be the problem, I don't think it's the thermostat, it is just a simple thermostat and I put the red and green wires together and still no blower. I tried switching the fan lever from AUTO to ON and still nothing. The outside unit comes on just fine and I can feel the cold air coming into the HVAC unit but the blower never kicks on and it doesn't sound like it is even trying to come on. Do I look to replace the circuit board at this time or could it be something else?

[RegUS_PatOff]

Check for 120V at the various calls for indoor blower by energizing "Y", "G", and "W" individually on the low voltage terminal strip.

Note that when "W’ is energized, the blower is delayed 45 seconds.

If there is 120V to each motor tap but the blower does not operate, replace the motor.

If there is not 120V at the Motor when "Y", "G", or "W" is energized, replace the control.

For service manuals and lots of other goodies,

become an Apprentice==> http://appliantology.org/apprentice/

[applianceman18007260692]

On gas heat type furnaces the blower uses 2 speeds Red for low speed heat and black for high speed ac

Electric heat uses one speed wide open.

So a way to switch speeds from low speed fan for gas heat to hi speed fan for air conditioning is done by use of a fan relay.

Older units use a relay, newer units use pc boards. Just thought I would throw that in.