I think I have a leaky vacuum line problem. The heater blows cool air in all positions except "vent' and there it blows only warm air. The cable operated blend door seems to be working fine. The heater core seems OK,
Fluid level is good and just put in new thermostat.
Does this sound like a vacuum line problem and where can I find a good chart of the vacuum lines on a 1992 6cyl F150xlt?