Question
what does MV stand for on the screws that hook up the valve wires? Sometimes the controller will not start the pump, sometimes it will what could the problem be?

Answer
MV is the Master Valve. Sometimes called a pump start. It sends a 24 volt signal to a relay which turns on the pump.
The first thing to do is to findout if the 24 volt signal is being sent. Next is to determine if the pump start relay is closing. This is fairly easy. Each time the controller is turned on you should hear a snap or click at the relay box. If this "click" happens every time then you need to check high voltage end of the pump. If your not familiar with electricity, I would recommend an electrician or qualified irrigation contractor. The power in the relay box can easily kill you.
Good luck, if you want instructions for testing the high voltage, reply back with as much info about the pump and relay.

Matt