air temp control issues!

i have a 1999 ford windstar 3.8 and get hardly any cold air using the air condtioner, i.m assuming the trap door is not operating by either closing or not closing the heater core therefore blending hot air through the vents.In other words the temp control is faulty. now for a quick fix to stop the heater core from getting hot water is a shut-off valve in line to the heater hose a quick fix for now so the air conditioner will at cool somewhat better?. I.n the mean time a replacment actuator control will fix the problem. Just wondering if this will work.

The actuator is right behind the radio... Easy to replace.