I have an old Craftsman door opener that has been opening on its own and have looked at all the possible causes and no fixes seem to work.
I removed wires from the wall-mounted opener so it isn't a wiring issue. The door opened while the remote was gone in the car so it doesn't look like a remote problem, plus it's new. I thought maybe it was a radio frequency issue. But when trying to reset the codes by pushing and holding the SR code button, the LED won't go out no matter how long the button is held down so the existing codes can't be erased. So I'm looking to see if this door opener can be reset by some other method.
I removed the wires at the opener itself so that should eliminate the wiring. The SR code button is yellow and the original remotes are long gone so no numbers from those. My opener doesn't have the photo sensors and uses force or torque settings for safety reverse. I have changed the plastic worm gears so it looks like it's time for a replacement seeing as that I can't reset the codes. I noticed the front sticker doesn't have a model number at all and the only number is 41A3625 which is on a sticker by the SR button. The original manual I have is
for a Model 139.18616sr 1/2 HP.
Best Answer
The most common cause of the door reopening is that one of the door limit switches is dirty or misadjusted. There are different switches to detect door travel and to sense the torque applied by the motor. The example below shows the switch that closes just before that door reaches the bottom of travel.
The two limit switches are at the end of the support rail. Try cleaning switch contacts, which get greasy from the rail lubricant. This is easy to do since contacts are exposed on many Craftsman door openers (not a hazard, since only 24 VAC at low current is used). Use automobile brake spray cleaner or other nonflammable, non-toxic (or only mildly toxic), solvent. The contacts are just below the end of the wire. If the door is open, you can clean between the leaves of the contacts with a cotton applicator -- being sure to remove any lint.
If that doesn't resolve the issue, loosen the switch from the rail and adjust forward or backward until the door closes properly and stays shut.
The purpose of the bottom switch is to sense the last few cm of door travel. The torque-sensing switch in the motor housing reverses door-travel direction if an obstacle is encountered, such as a child's foot on the door sill. However, the door must close with enough force to make a tight seal, preventing bugs and drafts from entering, so the bottom limit switch disables motor reversal as the door touches the sill. If that switch fails to close, the door reacts as if an obstacle caused it to reverse... sometimes, after a delay of a few seconds.