the garage door goes down but immediately reverses back up without hitting anything

Diagnosis

This behavior on the Craftsman 57915 is typically caused by a "false obstruction" trigger. The motor is programmed to reverse immediately if it detects too much resistance (force) or if the safety circuit is interrupted. In this specific model, the most common culprit is an improperly calibrated "Down Limit" setting. If the limit is set too deep, the door hits the concrete floor with too much force, triggering the internal force-sensing mechanism to reverse the motor to prevent damage to the door or the opener's drive gear. Alternatively, this is often caused by "sensor bounce" or misalignment. Even if the door isn't hitting an object, if the safety sensors (the eyes at the bottom of the tracks) lose their line-of-sight for a fraction of a second due to vibration as the door descends, the logic board interprets this as an object crossing the path and triggers an immediate reversal. You can confirm if it is a sensor issue by looking at the LED lights on the sensors; if the "receiving" eye (the one with the flashing light) flickers or turns off just before the door reverses, the sensors are the problem. If the lights remain solid and the door hits the floor before bouncing, it is a limit or force setting issue.

How to Fix It

To calibrate the down limit and force settings on the Craftsman 57915, follow these precise steps:

1. Clear the path of all debris and ensure the door is in the fully open position.
2. Locate the limit adjustment screws on the side of the motor unit. On this model, these are typically plastic screws labeled 'UP' and 'DOWN'.
3. Press and hold the wall console button to manually lower the door. As the door approaches the floor, watch the gap between the door seal and the concrete.
4. If the door hits the floor and immediately reverses, you must "back off" the down limit. Turn the 'DOWN' limit screw clockwise (tightening) by 1/4 turn. This tells the motor to stop the downward travel slightly sooner.
5. Run the door down again. Repeat the 1/4 turn clockwise adjustment until the door seals firmly against the floor without bouncing back up.
6. If the door still reverses despite a visible gap, you need to adjust the Force Adjustment Knob. Locate the dial (usually a small screw or knob) labeled 'FORCE'. Turn it slightly clockwise to increase the amount of resistance the motor allows before it triggers a safety reversal. Do not turn this more than a half-turn, as setting the force too high can be dangerous.
7. Test the cycle three times to ensure consistency.

If That Didn't Work

• Align and Clean the Safety Sensors: Wipe the lenses of both the sending and receiving sensors with a microfiber cloth and rubbing alcohol. Use a level to ensure the sensors are perfectly horizontal. If the sensor brackets are loose, the vibration of the door moving can cause the beam to break. Tighten the wing nuts on the brackets firmly against the track.
• Inspect the Tracks for Obstructions: Check the bottom 6 inches of the vertical tracks for accumulated debris, pebbles, or bent metal. Even a small piece of gravel in the track can cause the door to bind slightly, increasing the motor load and triggering the force-reversal mechanism.
• Check the Door Balance: Disconnect the opener by pulling the red emergency release cord. Manually lift the door halfway. If the door slams shut or crashes down on its own, the torsion springs are worn or improperly tensioned. An unbalanced door puts excessive strain on the 1/2 HP motor, causing it to "think" it hit an object.
• Replace the Logic Board Capacitor: If the motor struggles to complete the final few inches of travel and then reverses, the start capacitor may be failing. This prevents the motor from maintaining consistent torque at the end of the cycle. Replace the capacitor (typically 12uF or similar depending on the specific build date of the 57915) to restore full power.

Heads Up

• Safety Warning: Never disable the safety sensors to "fix" a reversal problem. This is a critical safety feature to prevent injury or death.
• Spring Tension: Do not attempt to adjust the torsion springs yourself. These are under extreme tension and can cause severe injury if they snap or slip.
• Lubrication: Lubricate the rollers and hinges every six months using a silicone-based garage door spray. Avoid using WD-40, as it attracts dust and grime which can cause the door to bind.
• Limit Screw Caution: Do not over-rotate the limit screws. Turning them too far in one direction can strip the plastic threads or cause the motor to attempt to drive the door through the floor or ceiling.