Is it too late for my evaporator coil in my central air conditioning unit ...

I have a Carrier Central Air System, product #FA4ANF036000AFAA. I am not sure how old it is, it was here when I moved in over 5 years ago. It has been freezing up, so I cleaned the evaporator coil on the inside, it was pretty dirty. That didn't work, so I called a repairman. He said I was low on freon (of course) and added about 6 pounds, but still it was freezing up. He checked for leaks, could not find any. He then cleaned id with the foaming cleaner, lots of crud came out. Still, it was freezing up and not getting the proper air flow.He told me " there was not much I could do" and that I needed a new coil, which would be about $300 for the part and about $700-$800 for labor and new freon. So after he left, I cleaned it some more, this time I ran the hose inside my house and really got in there. Made a huge mess.but got a little more grime out. Still, it was freezing, and not getting enough air flow. The blower fan works fine, but there seems to be no air flowing through the evaporator coil. There is almost no air flowing out of the vents in the house. When I remove the panel on the air handler, there is alot of suction, and the airflow out of the vents is normal again, since the blower fan is sucking in the air from where I opened the unit up, not through the coils.When I put the panel back on, air flow drops again to nearly nothing. Should the air be flowing right through the evap. coil without much resistance?I have nothing to compare it to, so I really don't know what a properly functioning coil "feels" like.Should light from a flashlight shine through the coils? Is there any definitive way to determine if the coil is beyond cleaning? I just don't want to buy a whole new one if there is some way I can "clear it out" more. Could the cleaning just jammed the crud up in there, clogging it like that? Additional Details: Some more details. Yes there is a new filter. that's the first thing I checked Also, I don't have a basement(Florida) and the air intake is right on the wall under the closet where the air handler is, nothing is blocking it. I pretty much know what the problem is: air is not going through the evap. coils, seems they are clogged. My main question, I guess, is does air usually pass through the coils easily(on a brand new unit? Because air is not going through mine. I just want to know if that is normal or not, how "breathable" that coil SHOULD be.like I said, I really have nothing to compare it to.

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