have a York Affinity model 8T and it has stopped cooling. The air handler is working and the fan on the out door compressor is working. I have two units and when I feel the copper tubing that comes out of the back on the one that works the pipe is cold. On the unit that is not working the pipe is warm. The unit is less than a year old and the contractor who installed it is no where to be found so I was looking for some advice on how to fix it myself.