I have a LiftMaster 1/2 HP from 2004 (sorry, don't know the model offhand). Just yesterday it started exhibiting this behavior:
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Opening the door works fine.
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When closing the door, it will travel 90% (door gets within 24" of ground) before reversing and blinking the lights. Subsequent attempts sometimes repeat same behavior, but often will reverse immediately or within the first 5" of travel.
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When the sled is detached from the door and the door is in the raised position, the sled will travel properly both down and back up 100% of the time. So this problem has nothing to do with the safety sensors or wiring.
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When the sled is detached and the door is in the closed position, the behavior of the sled matches #2 above. The sled will mostly immediately reverse or travel a few inches and reverse.
Notes:
- Have tried power-cycling the unit.
- The door is fairly well balanced and I have no trouble opening/closing it manually.
Appreciate any ideas. Thank you!
Best Answer
I disagree that the problem has nothing to do with the safety sensors...in particular, the optical beam which is placed near the bottom of the door.
Check and make sure there aren't cobwebs or leaves or any other crud on the emitter and sensor or hanging down from the door itself which could fool the door into thinking there is an obstruction.