How do you determine if a sub-cooler is bad on a rack? Alarm set point is above 80 degrees. When I got there was reading 91. Being feed from med. temp. rack with a sport. Backed sport all the way out to rack pressure and turned in the manual stem in the liquid solenoid valve. TXV seemed to be feeding. Suction comming from med. temp. rack was hot and would never get cold after about an hour. I suspect the heat exchanger has a leak in it but not sure, how can I verify? Or is the TXV not feeding? Help !!!! Both racks are R22 Luckly if the sub cooler is bad!