1997 T&C AC Problem

The AC on our 97 T&C works fine after it is first turned on. For the first 30 minutes or so of driving I can feel the AC compressor cycling on and off as the temperture stays cools. However; after about 30 minutes the AC compressor turns off and doesn't come back on. I've waited for the interior temperature to get fairly hot and it never comes back on. But if I turn off the compressor using the AC button or turn the Fan off and back on the compressor turns back on and cools very well for a few more miles and I can feel the AC compressor turning off/on to maintain a constant temp. After a random amount of time it tuns off and I have to cycle the switch off and on again.

I've taken the control panel apart and cleaned all the temperature sllider contacts and checked all the connections. I''ve no idea where the temperature sensor is that controls the temperature - so I haven't checked it.
Has anyone experinced this problem or have any suggestions.

Thanks.