Chamberlain HD420EVP Owner's Manual page 31

Adjustments
STEP 2 Test the Safety Reversal System
Without a properly installed safety reversal system, persons (particularly small children) could be
SERIOUSLY INJURED or KILLED by a closing garage door.
Safety reversal system MUST be tested every month.
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After ANY adjustments are made, the safety reversal system MUST be tested. Door MUST reverse
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on contact with 1-1/2" (3.8 cm) high object (or 2x4 laid flat) on the floor.
1. With the door fully open, place a 1-1/2 inch (3.8 cm) board (or a 2x4 laid flat) on the floor,
centered under the garage door.
2. Operate the door in the down direction. The door MUST reverse on striking the obstruction.
If the door stops and does not reverse on the obstruction, the down travel needs to be increased (refer to
Adjustment Step 1). Repeat the test. When the door reverses on the 1-1/2" (3.8 cm) board (or 2x4 laid
flat), remove the obstruction and run the opener through 3 or 4 complete travel cycles to test adjustment.
If the garage door opener continues to fail the safety reversal test, call a trained door systems technician.
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STEP 3 Test the Protector System
Without a properly installed safety reversing sensor, persons (particularly small children) could be
SERIOUSLY INJURED or KILLED by a closing garage door.
1. Open the door. Place the garage door opener carton in the path of the door.
2. Press the remote control push button to close the door. The door will not move more than an inch
(2.5 cm), and the garage door opener lights will flash 10 times.
The garage door opener will not close from a remote control if the LED in either safety reversing sensor
is off (alerting you to the fact that the sensor is misaligned or obstructed). If the garage door opener
closes the door when the safety reversing sensor is obstructed (and the sensors are no more than 6
inches [15 cm] above the floor), call for a trained door systems technician.
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