3.5 cubic foot igloo freezer green light won't shut off

The green light may have failed without affecting operation.

Compressor may be bad. Also could be the relay that plugs into side of compressor that’s bad. Inexpensive, easy to replace part if it’s the relay.

What if the red light is on and the green light is off what's the problem

The door sometimes warps and need to be lightly twisted back to where all four corners make contact and seal.
Your unit may need to be tilt back a bit so the door wants to close y itself, the front foot pegs are adjustable and can be turned to make the front higher or lower than the back side of the cooler, gravity closes the door when the unit is leaning back.

It may be on "superfreeze", if there is a yellow light, or it may be set for too low a temperature (try setting the thermostat down to 1 or 2). Check the condenser is clean, and fan working if it has a fan, Check lid is closing properly and the ambient temperature isn't too high.. Lastly, if all else working correctly, suspect short of refrigerant.

Pretty good chance it is a t-stat problem, overshoot and undershoot.

replace t-stat.

it may be caused cooling problem.

I'd let it dry out totally then try it again, some of the electronics may have gotten wet when you defrosted it. Give it a week somewhere warm and dry like a garage. If you didn't attack built up ice in the freezer with a knife while defrosting it it should work after it dries out. Most people end up killing freezers by accidently poking holes in the evap coil while trying to remove built up ice.

I would have to say yes if you can not do the repairs yourself. "some" not all parts have been discontinued and no replacements have been sugested.

The higher the number, the colder.