Frigidaire Thermostat Problems

A year or so ago I pulled the thermostat housing and air duct off the ceiling of my Frigidaire top freezer refrigerator. The temp probe is about 18" long and is routed to the back of the refer, down under the air ducts, then back up into the housing. It's in a plastic jacket tube, I disturbed it last year while tracking a water drip and the refer has NEVER gotten cold enough since then. With the thermostat setting at full cold it's still in the mid 40s. Changing the air flow control in the freezer section makes no difference.
So, I just bought a new thermostat believing the old one bad. No change!!??
Do I have the probe routed wrong? Should the end be covered or uncovered? Does it stick into the styrofoam air channeling stuff? What the hey?
Thanks for any clues!
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