I also see where Jim is going; but, if that was the case, I would think the gauge may swing to Hot more frequently and even possibly end up damaging the gauge.

The sending unit is essentially a variable resistor, with higher resistance when cold and lower resistance when hot.

Try poorman212's suggestion to unplug the sending unit wire connector, turn on the car and A/C.

 

Right, I know the gauge went up when he tested it. But I thought the gauge went up somewhat erratically (maybe not all the way) & that was the problem.

A gauge erratically moving down would be an intermittent open-circuit.