Does anyone know which hose is the heater inlet hose? When standing in front of the truck with the hood up I see the two hoses on the passenger side going into the cab. I cannot tell which one goes to the water pump (heater hose inlet is usually the one that goes to the water pump) but the 99 V10 water pump has no hoses connected to it. Looks like hardline behind the water pump but I can't tell which of the two heater hoses the hardline connects to because the hoses exit out of the back of the block and I can't get a good look. Installing a bypass valve and need to know the direction of coolant flow. No luck in search...

 

On the fire wall looking in. The one on the left outlet from pump and the one on the right inlet return to block. You can see the inlet[return] hose attached to about half inch tube which bends 90 deg drops 6 inches and meets the intake manifold.
Hope this helps good luck.

 

Ok...so hose that is the closest to the passenger door is intake to heater core? Antifreeze flows left to right looking at the two hoses from the front of the truck. Then if valve has arrow marking flow I would splice the valve into the leftmost hose? Only real worry is if valve is not spliced right (flow against the arrow instead of with it) it may not work well. Thanks for the info...please let me know if this is right.

 

Sorry but i posted wrong info earlier.
When I looked at Alldata it shows the pipe coming from the intake manifold as the heater core inlet hose[right one at fire wall] and the other one as the heater core outlet.[left one at fire wall].
So completely backwards from what I originally posted

 

http://www.frontiernet.net/~jmray/F250ColdAC.htm

I did this to my 2001 F250 with Napa Heater valve #660-1867, 8 feet of vacuum hose, and a brass aquarium Tee. This will only shut the valve when in Max A/C mode. Once it is cold, I switch to A/C mode to allow the water to flow thru the heater core. It works great!

 

The vacuum Tee splice is located under the dash, on the passenger side. It was tough to get the vacuum hose thru the grommet. The hose will come out behind the fender well and it is simple to route it to the heater valve.