2002 Chevy Tahoe Rear air doesn't work properly

Thanks for looking at this problem, the rear air in my 2002 Tahoe is not cooling. The fan works fine but the air is not cooled. The thermal expansion valve for the rear was replaced appx 6 months ago because of this same problem. After the replacement of the expansion valve, the air seemed to be a little cooler but not much. This condition reappeared when I took a trip to Florida last week. The rear air is seldom used and so I am not sure how long the rear air has not been cooling. Is it likely that I received a defective expansion valve from the Chevy dealer or is there another possible cause of this problem? The front air works very well. Thanks for your help.
I did make a donation via paypal Transaction ID #78812557D4538773J
ray1jay@comcast. Net