What is the model number?

The model number is 139.53920DM.

The lights do not blink when the door meets an obstruction only when something breaks the beam between the door sensors. Back off the down force until the door will not close and then increase the down force only enough that the door will close consistently. If the door still doesn't reverse on the 2 x 4 and the opener is still in warranty call Sears. It doesn't matter that you installed it yourself.

On page 28 of the manual under the heading "How and when to adjust the forces" Item 1 (Test the DOWN force bullet 2 (If the door reverses during the down (close) cycle and the opener lights aren't flashing ...) I read this as the lights should flash. I increased the force in small increments until I reached the max limit and couldn't get the lights to flash.

Do you think the closer is defective or do you have any other suggestions?

You are reading it wrong. The door will reverse under two conditions. One is if the door meets an obstruction or the door is binding. It will simply reverse to the open position. The other is if there is something blocking the beam between the door sensors. The door will then reverse and the main light will flash 10 times. This helps with diagnosis.