As an expansion to what MBDOC is saying, you can pull the electrical connector off the watervalve, then tap a power and ground to the 2 pins on the valve, you should hear it tap or "thunk" inside the valve when you apply or disconnect the power. If not, the valve itself is "bad", not just the insert. If it seems to be acting correctly, try hooking up a voltmeter to the 2 sockets on the connector and monitor the voltage while running the climate control. In the "hot" side, there should be almost no power. It cycles though, not modulates, so your looking for almost "zero" volts, or almost battery volts, no in-between readings. So on "HOT" it should almost always read near zero, it may show a battery voltage spike from time to time. Just the opposite on max cool, it should almost always show battery voltage, but may cycle to no or almost zero volts occasionally, just to help keep the evaporator from freezing over. If it isn't working correctly, the problem typically is the push button panel/control unit (the part with the buttons on it that controls the climate control). The reason the valve is set this way is so if there is a power failure to the valve, they want to make sure that heat is able to get into the cabin to keep the windshield clear. As a matter of fact the failsafe for the distrubution system is to divert air to the windshield, and for the fan control it is max fan speed. We have had several customers come in with max heat, on the windshield, and full blower speed, on 90 degree days, too! Some came in in the middle of winter too, they didn't complain as much!
Gilly