I have a Lennox G43UF series furnace with a/c. The blower runs, but the a/c compressor is not running. I checked the contactor at the compressor and it is not making contact. I checked for the obvious loose wires etc. but found nothing. I checked the thermostat and it is sending 28 volts to the yellow and green wires to the furnace control card. What else can I check?