Chrysler Repair: Chrysler voyager heating system?, air distribution system, chrysler voyager

Question
i have a 1998 voyager 2.5td.recently there is a hissing noise when i turn on the air/heating control.it is not the brake system.it may be the valve/pump connected with the water flow in the heating radiator .any ideas? roland? thanks.

Answer
Hi Francis,
There are at least two possible pressurized systems that are part of the heater/AC unit: the heated coolant and the refrigerant. I will have a '98 Chrysler shop manual in a day or so and will have more specifics but for now I would try to determine if the hissing noise is associated with only using the heat (which would implicate a leak in the heater core) or with the AC (which would implicate either the refrigerant evaporator or the heater core because both are needed). Also note whether you are loosing coolant and whether there is any dampmess in the carpeting under the dash which would implicate the heater core. Any filmy deposit on the inner surface of the windshield would implicate the refrigerant. Of course if the refrigerant is leaking then in the near future the compressor will refuse to operate due to a disconnect switch for loss of pressure.
Finally, there may be a vacuum line associated with operation of the air distribution system, but I believe that the air doors in the later 90's were all electrically controlled, so that is unlikely to be the source of the hissing sound.
Roland