Contrary to popular belief, the electric opener does not provide the actual lifting power to open and close a heavy garage door. Instead, the actual lifting power comes from the counterbalance springs that are under tension to lift the garage door via steel counterbalance cables.
The electric opener itself consists of a power unit that contains the electric motor. The power unit attaches to a track. A trolley connected to an arm that attaches to the top of the garage door slides back and forth on the track, thus opening and closing the garage door. The trolley is guided along the track by a chain, belt, or screw that turns when the motor is operated. A red handle and rope are attached to the trolley to allow the garage door to be disconnected from the opener for manual operation or in case of emergency. Limit switches on the power unit control the distance the garage door opens and closes once the motor receives a signal from the remote control or wall push button to operate the door. Many safety devices are available and required to insure safe operation from day to day. It is imperative that you test the safety of the reverse switch and optic eyes during a home inspection.
The entire assembly hangs above the garage door. This assembly should also be inspected for installation issues. The power unit hangs from the ceiling and is located towards the rear of the garage. The end of the track on the opposite end of the power unit attaches to a header bracket that is attached to the header wall above the garage door. The power head is usually supported by punched angle iron.
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