Garage door opener malfunctions can seem perplexing, but the fault is usually related to improper adjustment of the travel limits and force controls or poor alignment of the safety sensors. The adjustment screws on Craftsman door openers are on the opener unit -- the pair on the side of the unit regulate opening and closing distance, and the pair either on the back or the opposite side regulate force. You may need to adjust both parameters. Always test the opener's safety reverse system after making any adjustments to the opener or repairs to the door.
Craftsman and all other recent door openers are equipped with safety reverse sensors and a safety reverse system. The sensors are the "eyes" that send a beam across the door opening and stop the door from coming down when an obstruction interrupts the beam.
The safety reverse system is a pressure-senstive mechanism that automatically reverses the door when it meets an obstruction upon closing. This system is related to the travel and force settings of the door, so you must test the safety reverse system after making any adjustment to the travel limits or force, or after making door repairs or any mechanical adjustment to the opener, such as tightening or loosening the chain.
To test the safety reverse system, place a 2x4 board flat on the garage floor in the center of the door opening. Activate the door so it closes onto the board. The door should reverse direction and open once it contacts the board. If it fails to reverse, increase the door's Down limit slightly and retest.
Up and Down Limit Adjustments
The limit screws determine how far the door travels in either direction before it stops and must be adjusted to conform to the size of the door opening. Run the door through a complete cycle and observe where it stops. If it doesn't open all the way, but opens at least 5 feet, turn the Up limit screw clockwise with a screwdriver to increase opening distance. One complete turn of the screw equals 2 inches.
If the door doesn't close all the way, turn the Down limit screw counterclockwise to increase the travel distance. If the door still doesn't reach the floor, you may have to lengthen the door arm.
If the door reverses as soon as it touches the floor, decrease the down travel by turning the Down limit screw clockwise.
The force adjustments, usually located on the back or right side of the opener housing, regulate how much force is needed to stop the door from moving. If the force setting is too light, the door stops easily in the up direction, and when going down, any gentle pressure will make it reverse. If the door behaves erratically, it could be related to improper force adjustments.
Test the Down force by activating the door so it begins closing. At the halfway point, grab the bottom of the door and apply upward pressure, as though you're stopping the door's travel by force. The door should stop and reverse direction when only light upward pressure is applied. If it fails to reverse or reverses only with heavy pressure, decrease the Down force by turning the adjustment screw in the direction of the arrow imprinted on the housing, using a screwdriver. Make only 10-degree adjustments at a time, retesting the door after each adjustment.
If the door reverses by itself or with almost no pressure applied, increase the Down force by 10 degrees and retest.
Test the Up force in a similar way: Activate the door so it begins to open, then stop the travel by grabbing the bottom of the door at the halfway point, applying downward pressure on the door. If the door fails to stop or won't stop without heavy pressure, decrease the Up force by 10 degrees and retest.
If the door stops on its own or won't open farther than 5 feet above the floor, increase the Up force in 10-degree increments.
Note: Each screw turns only through 260 degrees -- adjust 10 degrees at a time, and don't try to exceed the 260-degree limit, or you will damage the mechanism.
The Safety Sensors
The pair of sensors attached to the door track about 6 inches above the floor prevent the door from closing if there is a person or object in the door's path. When the sensors aren't adjusted properly, the door won't close. Check the lights on the sensors -- the sending sensor has an orange light that glows steadily, while the receiving sensor has a green light. If the light on the receiving sensor is off, dim or flickering, it means the receiving sensor isn't detecting the beam from the sending sensor. That may mean something is in the way of the lens. If not, you need to adjust the alignment.
Troubleshooting the Sensors
Before aligning the sensors, make sure both lenses are free of cobwebs and that nothing is hanging from either door track that could get in the way of the beam. If you persistently experience problems, particularly at certain times of the day, it may be because one of the sensors is in direct sunlight -- consider shading it from the sun. When adjustment is required, loosen the bracket holding the sending sensor and move it carefully until the light on the green receiving sensor glows steadily, then tighten the clamp.