I have a 1999 dodge conversion van , first when a/c or heat is turned on air comes out of defroster of floor not center vents for about a minute than it go to normal a/c center vents. also a/c max speed is the same as normal a/c speed, I lost a/c max high fan speed. any ideas anyone?

 

A/C and Max A/C are the same fan speed electrically. It sounds louder and might be slightly faster because on Max the outside air vent is closed off. First this creates a resonance within the ductwork making for a higher noise level. Second, when the outside vent is open, the fan is trying to pressurize the cabin which causes the fan to slow slightly because of the air resistance.

You have a vacuum leak. That's why the air isn't blowing out the center vents. The lack of vacuum would also keep the outside vent from closing, thereby eliminating the Max A/C feature from working. This is giving you the impression that you've lost the higher fan speed which I covered above.

 

Check for a cracked nylon vacuum line. I have seen many cracked near the PCM on the firewall. Also not uncommon for the line to get loose from the vacuum bulb behind and slightly below the passenger side headlamp assembly.