Information

If you're referring to the valve in one of the heater hoses, it's purpose is to stop the flow of hot coolant when the air conditioning system s running. That reduces the load on the AC system and makes it more efficient. If that valve is removed, the air from the air conditioner might not be quite as cold as it is now.

Its other purpose is you DO want that valve to allow coolant to flow when you select the "defrost" position. The AC system runs in defrost mode to condense out the humidity before it blows the heated air onto the windshield where it would cause fogging. You'll also find that a wet windshield on a rainy day will clear up within a few seconds when running in defrost mode, as long as the AC is working. In hot climates, some people block the heater hoses, especially if something is leaking. The AC system will still remove the humidity from the air, but being unheated after that will make it take a long time to clear the inside of the windshield.