To determine if it's the valve or the pushbutton panel, that's pretty much all my previous post was about. Do the test by jumping power and ground and see if the valve thunks. If it does, the valve is OK, end of test. Then you should monitor the voltages as I suggested in max hot and max cool just to verify the pushbutton panel is in fact faulty. To test the valve, you need a pair of test leads with alligator clips on one end of each. The battery is near the valve, so it's pretty simple. Clip one of the leads to battery positive side, the other to the negative side. The valve is not sensitive to polarity, so it doesn't matter which side of the valve you put the power or ground to, it should "thunk" either way. Anyway, just touch the ends of the test leads to the two pins on the valve, power on one, ground on the other. If your aren't 100% sure the valve is operating, just get someone to either feel the valve or do the wire jumping so you can feel if it's working or not, it's usually pretty obvious if it works.
Gilly