Chamberlain LiftMaster Professional SW420 Installation And Maintenance Instructions Manual page 22

22
Limit Switch Adjustments
5 Press the CLOSE button or connect terminals #3 & #1 or #3 &
#2, depending on which installation you have (left or right hand
opening). The OPEN/CLOSE button is a constant pressure
function.
If the control arm does not start to move, the close limit cam
may be already actuating the close limit switch or an improper
electrical connection may have been made. Turn off power,
inspect and correct the situation, and repeat this step.
6 When the control arm is pointed in the approximate direction of
the gate bracket (on the fully closed gate), press the
button or release terminals 3 & 1 or 3 & 2.
If the control arm does not stop, the STOP button was
improperly connected. Turn off power, inspect and correct
the situation, and repeat steps #3 and #4.
If the close limit switch has been prematurely actuated, turn
off power. Loosen the set screw on the close limit cam and
rotate the nut away from the close limit switch. Repeat steps
#3 and #4 until the control arm is pointed in the correct
direction.
7 Turn off power! Be sure the close limit cam is freely turning.
Rotate the cam in the same direction as the shaft turns to close
the gate. Stop at the point at which the cam just clicks the
close limit switch. Tighten the set screw securely.
8 Connect the gate bracket back up to the extension arm.
If the arm has moved too far in the close direction to allow
connection of the gate bracket, turn off power, press the
OPEN button to rotate the arm back a short distance in the
opposite direction, and press the STOP button when the arm is
in the desired position.
9 Turn on power! Press the OPEN button (with constant
pressure) or connect terminal #1 and #3 (or 2 & 3, depending
on right or left hand operation) on the control terminal strip.
If it does not, the open limit cam may be already actuating the
open limit switch or an improper electrical connection may
have been made.
10 When the gate reaches the desired fully open position, press
the STOP button or release terminals 1 & 3.
11 Turn off power! Be sure the open limit cam is freely turning.
Rotate the cam in the same direction as the shaft turns to open
the gate. Stop at the point at which the cam just clicks the
open limit switch. Tighten the set screw securely.
Doc 01-G0610
Rev A
The control arm should start
to move in the direction that
would close the gate if it
were connected.
The control arm should
STOP
stop.
If the control arm does not
move far enough to point in
the proper direction, the
close limit switch has been
prematurely actuated.
The close limit switch is
now "coarse set."
The gate should start to
open.
Turn off power, inspect
and correct the situation,
and repeat this step.
The gate should stop.
The open limit switch is now
"coarse set."