Thank you very mush for your input.
The opener connects to a chain, and the chain moves a gliding bar on
the rack. The gliding bar is engaged with a metal hook, which
connected to the garage door. When gliding bar and hook locking
together, the garage door start to move along with the movement of the
chain and open and close the door. When gliding bar and hook
disengaged, the gliding bar will move itself back forth on the rack
without move the door. I hope you know what I am talking about.
Here is more interesting observation. My problem with my garage door
opener seems related somewhat with the connection of the bar to the
hook. When the bar is off the hook, it is much more easy to start the
opener to move the bar itself. Once the gliding bar engaged hook
during motions, it will drag the door to open or close easily. When
the bar or hook in a locking in position, it will take 10-15 push of
button to start move both of them.
Now each time we want open our garage door, we have to physically go
to the door, pull the string disengage the hook with the gliding bar.
We have to come back push the button to move the opener, normally the
opener will move the bar in 1-2 pushes. After the opener running, bar
is gliding, engaging the hook in motion, dragging the door to open.
When we close the door, we have to physically disengage the bar and
hook, everything work in a reverse way.
But if we want to open the garage door directly, we have to do at
least 10-15 pushes of button.
Please help. Thanks a great deal!