are you getting a click when the thermostat cycles on as If it is outputting a signal to tell the ac to turn on? Of not your thermostat coould be bad. If your capacitor is bad it will most likely be egged shaped on the bottom or leaking. They are like $40 and easy to change out. Just don't touch both contacts at same time in case the capacitor is still holding a charge. Reassemble in reverse order.
are we sure we have a gas furnace? have you seen the circuit board? is there a flue pipe similar to a gas Hot water heater on unit in attic. the model number you posted was a 3 ton outdoor 13seer condenser.
was in ac business for 30 plus years, for my self since 93. Started building houses in 94 and did both till 07 and shut down a/c bus. got too old to do work. kept building till last fall. Now I just count my money and hunt and fish.
Light not burning on circuit board-possible bad breaker, burned wire in elec panel, power kill switch in attic, or at door switch. also possible bad door switch. light blinking- control problem. too difficult to diagnose over internet. light burning- with blown fuse on circuit board which means you probably have a short in controls or t stat. light burning and fuse on board good- normal operation. probably problem with control wires to t stat or t stat it self. good night