It's called the reversing valve and it does what it says, it reverses the refrigerant flow. And yes, you are correct, it is operated by a solenoid.?If?....you have a heatpump/ac, you may have a failed solenoid! There is a solenoid that ?switches? , the refrigerant flow....either giving you cooling or heating! If you are in the cooling mode, you will get ?hot? air discharge from the ac condenser on the roof. Just the opposite in the heat mode.