Garage Door Sensors work in reverse?

HVAC & Fireplace Bucket EXPERT April 10, 2008

If your door closes when the safety sensors are triggered I would recommend disconnecting the opener and manually operating the door only until the issue is resolved. The door could easily close on someone since it would actually close if someone walks through the safety sensor area under the door. You did not include a model number, but even smaller openers have enough power to hurt or even kill someone trapped under the door, which is why the safety sensors were developed to begin with and are now mandated by law.

The safety sensors themselves only note a change in reading. And, as a fail safe, the control board of the opener is designed to only react to that change in one direction so the problem in this case is likely not with the sensors themselves.

Specifics vary from model to model, but it is possible to install the lift chain or belt reverse from normal. On some models it is also possible to install the trolley backwards. Then the door lift would go opposite of the intended direction, opening the door when the opener is triggered to close. Since the door travel limit switches stop the door based on relative positions only they could be adjusted until the door still appears to operate normally but the opener would still see the "door open" position as "door closed" and vise-versa. So as soon as the safety systems were triggered the door would close instead of opening.

The detailed information and illustrations on installation and assembly in the Owner’s Manual should help you figure out if something was assembled incorrectly. You can use the "139" model number off the overhead opener unit to get your manuals online. Go to the Home page of Manage My Home and hold your mouse over the square labeled HOME in the upper left of the page. A drop-down menu will appear, choose the option Products and manuals and then enter the model information and follow the steps.

As mentioned, the symptoms you described are dangerous so if you have any remaining doubts or concerns you should consult a professional to be sure the problem is addressed and the door operates safely.