the same as all problems on jeep's the vacume system.and shitty connections.I have fixed 3 jeeps this week the first the shift fork in the VDA was broken,some one tried to shift on the fly at to high of speed and broke the fork.Erins was leaking oil and expanded the plug and it fell off clean it up and a litte silicon good as new.The heaters blowing cold air is the connection on the top of the heater assembly in behind the radio.is it either fell off.is jamed open with junk or the vacume pot is bad in is holding the door open or closed.