2004 Jeep Grand Cherokee knob only blows to defrost

jeep
grand-cherokee

#1

control knob only blows to defrost, what is the problem


#2

I suspect that your Jeep has manual HVAC controls, not ATC and the vacuum supply line is disconnected from the engine. The rubber vacuum line connector at the engine will sometimes swell from contact with oil in the intake manifold and the line falls off.