The freezer is not defrosting. I noticed that frost was on the food and after removing the top shelf I noticed ice build up on the vents. I am think it was caused by the freezer being packed full and no air could flow thru the vents. Could that possible be the reason? Not sure how to force defrost mode either. Any help would be great.

It is an LG so getting any tech info on it will be a pain.

I doubt that you have a defrost problem except for one possible scenario, see below.

Defrost does not mean getting frost off of frozen food items.
It should only melt frost/ice off of the evaporator/freezer coils.
By the sound of it you have heavy frost on the food. Normally it should just be a light coating.

The frost is moisture that is condensing on the frozen food so I would try to figure out where that moisture is coming from.

The first place I would check are the door seals.
Make sure they are clean and visually inspect them to see how they are sealing.
Take special note of the hinge side. Sometimes that side can grab onto the frame and twist when it is closing. If it does this then a light coating of white lithium grease or vaseline should fix it.
Check that the hinges are OK and doors hang level.
Check that the unit is level front to back or leaning slightly to the back.
Take a two inch wide piece of paper and place it between the door seal and the units frame. Then pull it out to see how good the seal is. Work your way around both doors.

Another possibility is that the freezer compartment is actually getting too warm every once in a while.
Take a bowl or cup of ice cubes and put them in the freezer.
Give it a couple days and then check them. If they are all frozen together then the freezer has gotten too warm.
Check the freezer temperature. It should be between 0 and 5 degrees F.

If they are frozen together than there are a couple possible problem causes.
1. When the unit defrosts the heater should shut off when all the frost/ice has been removed from the evaporator coils. Perhaps it is staying on for too long of a time and slightly melting items in the freezer.

2. There is a problem with the temperature control and it intermittently gets too warm in the freezer.