Why doesn't my air conditioner fan come on when the condenser starts?
Mark and remove the wires from R and G. Add a jumper wire across R and G. You should hear a click (that's the relay on the board) and the motor should start. If not check your capacitor (little oval device attached to this blower housing) be very careful as capacitors can give you a massive shock even when powered down. They are essentially high capacity, quick charge/discharge batteries. The rating printed on it should be around 5-10 micro farads. The reading on your multimeter should be within 1 of the printed value. Also check for power output of 120v on the fan terminal (most likely low cool with G jumpered High cool with Y jumpered) on the board with your other lead to ground. No 120v on the high or low cool terminal with R jumpered to G, your board is fried. Yes 120v your capacitor or motor is fried if the cap is good and the motor is bad change the cap and motor together.

There are elements to this diagnostic that are potentially harmful and should not be done by the average DIYer. Hopefully it's the cap. Easy and cheap fix.