While changing the oil today I noticed that there is a broken line visible on the top rear left side (when looking at the truck) of the engine. It appears to be a vacuum line running to a valve on the OB coolant hose for the heater core. I've got the line patched using some shrink tube that I had lying around. The valve does appear to operate after I patched the line.

What does this valve do?
How difficult would it be to replace the broken line? Is it worth replacing, or is it fine patched as long as the valve appears to be operating when the truck is running?

Thanks for the help!

 

That valve is likely there to stop the hot coolant front entering the heater core while you have temperature control turned to cold.