Dodge 2006 Ram Pickup 2500 - Manual (Page 284)

Circulation
The cab is designed with features to promote outside air
circulation. There are grilles in the cab back panel. These
are air exhausters that provide the means for regular
exchange of cab air.
Side window demisters direct air flow specifically to the
window glass to help prevent interior fogging of the
glass. They are located in the extreme outside upper
edges of the instrument panel. The demisters also pro-
vide extra air ducts for circulation. They are in operation
whenever the Floor, Mix or Defrost modes are in use.
NOTE: When you turn off the engine you may hear a
hissing sound from under the hood for a short period of
time. This is a normal condition that occurs if the air
conditioning system has been on. It is not an indication of
a problem with the air conditioning system.
Rear Air Duct—Mega Cab Only
The rear seat will receive air flow in all modes except for
Defrost.
The rear air duct is designed to be pointed up when in
A/C mode, and pointed down in Heat mode.
Mega Cab Rear Air Duct
284 UNDERSTANDING YOUR INSTRUMENT PANEL