I had a call for AC not cooling the apartment. Found upon call for heat that the blower was not coming on. Tested unit in heat mode and fan only mode. Blower worked fine but upon a call for cool the blower shuts off. Blower is 240 volt. Blower capacitor is ok. Blower motor is ok. Suggestions?
It sounds like a faulty blower / ignition control board. I would just figure out which fan speed is energized when the thermostat fan switch is set to ON. Swap that wire for the black high speed cooling wire as a temporary fix until you get a new control board. You'll have to leave the fan running continuously until the part is replaced.
Lennox might sell the part you need.