Most Massey Ferguson Cab Tractors feature a Coolant Flow Valve that allows you to control the Engine's Coolant flow to the cab. The Engine Coolant is used to heat the cab. IN the Summer you want to make sure this valve is in the off or crossways position so the air conditioner is not trying to cool the circulating coolant. Now that it has gotten cold you want to make sure it is on so you heater works. This video shows the location on the 4700, 5700 & 6700 Global Series plus 5700SL, 6700S & 7700S Premium Full Featured Tractors.