I posted this in the V10 section thinking the hose/valve are V-10 specific but not sure so I thought I would see if anyone here knows where the hose connects and can tell me what the valve is?

https://www.ford-trucks.com/forums/9...tion-hose.html

 

Is it a heater core shut off valve? Kind of looks that way. I know some trucks came with a valve that shuts coolant off to the heater core when using the AC.

 

It s a coolant shut off valve. The The heater cores in the superdutys would build up a lot of heat under the dash during the summer. People have been installing coolant shut off valves to prevent this. One end of the vacuum line attaches to the nipple on the valve and the other end is t'ed into the red vacuum line on the back of the heater control in the dash. The red vacuum line is accessible behind the glove compartment. The heat will only work when set to floor or defrost. In the AC or vent mode the hot coolant will be shut off to the heater core. Its a great mod. On cool evening you can set it to vent and cool air will blow instead of warm.
Budman

 

It also cuts off the heater core for Max AC. Plug the fitting onto the fitting on the end of the cylinder, typically. You may be noticing weird vent behavior on Max AC as you are currently venting the system to atmosphere through that disconnected hose.

-Dave

 

Thanks everyone, the system seems to work better with the hose connected

 

If the vacuum hose is connected to the vacuum line behind the dash but not into the control valve you will have a vacuum leak. This could cause the CEL to come on and possibly cause the truck to idle rough. If you decide not to use the coolant control valve you should plug the vacuum line.
Budman