Its pretty easy. The climate control diagrams show you how to do it. You don't need the test unit, just hook up a multimeter to the pins on the connector that are being tested. The test diagrams also show you how to cheat the thermistor to test the CCU. You'll be able to tell pretty quickly if your sensors or relays are working correctly. Also, the temp wheel is basically just a couple of connections and a variable resistor. When you take out the CCU take the wheel apart. There's a ball bearing in there, don't lose it. You may have a bad connection to the variable resistor. Clean all the contacts and check the resistance - I think it went from 0 to 8K or 10K ohm. Reassemble and see if operation returns.
Good luck!