A typical air conditioning condenser unit has two types of capacitors. One of those, the run capacitor, helps maintain a constant voltage supply to the motors that run a compressor and fans. The second type is a start capacitor, which is a device that gives a voltage boost to the unit's motor.
If an air conditioning condenser is having trouble starting, including any of the motors that run inside the unit, replacing the start capacitor may solve the problem. If the motor is noisy or overheating, it could be a sign of a faulty run capacitor. As of 2010, replacing a defective run capacitor costs an estimated $123 to $164, and replacing a faulty start capacitor costs between $132 and $176, according to AllAboutHome.com.
To test if a capacitor is working properly, a service technician uses a multimeter, an instrument that measures voltage and resistance.