Hi,
A few months after I got my 99 my Heater/AC controls would work intermittedly most of the time only blow out of the defrost and floor vents, I had a post questioning if it could be a vacuum pump though when I checked by the fire wall it was well within spec
Found it was the little black box on the bottom of the EVAP case near the center hump (pain to remove), it has a electric motor in it had one go bad on my Gas 01 due to a bad heater core (shorted it out) and forgot about it, but I swapped it out this weekend on my Diesel and solved my issue, figure I would share
Regards,
Jim
A few months after I got my 99 my Heater/AC controls would work intermittedly most of the time only blow out of the defrost and floor vents, I had a post questioning if it could be a vacuum pump though when I checked by the fire wall it was well within spec
Found it was the little black box on the bottom of the EVAP case near the center hump (pain to remove), it has a electric motor in it had one go bad on my Gas 01 due to a bad heater core (shorted it out) and forgot about it, but I swapped it out this weekend on my Diesel and solved my issue, figure I would share
Regards,
Jim