1999 Dodge Caravan Hissing sound while A/C on

Tiny
KILROY0097
  • MEMBER
  • 1999 DODGE CARAVAN
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 85,000 MILES
I have recently worked on my A/C which required me and an auto mechanic friend to completely remove the dash down to the firewall in order to replace the evaporator which was corroded and leaking coolant. We replaced that, replaced all O-rings, the blower and replaced the conditioner/drier for the A/C system. The compressor was replaced in 2004. After all was said and done we recharged the system and also tested vacuum pressure. Everything was fine and it has worked great for several months. Now there is a hissing sound that travels between the front dash and the back of the van near the rear A/C blower. This van has two blowers for front and rear passengers. The A/C is not working as well as it was and I'm afraid that it either has a leak or there is some kind of pressure issue. The hissing sound is very similar to the sounds I heard when my A/C broke the first time. Anyone have any ideas on why there might be a migrating hissing sound traveling from front to back to front to back?

BTW when I turn the A/C off it takes a few seconds for the hissing sound to stop but it does stop. Blower fans on without A/C turned on does not making hissing sound.
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Thursday, August 12th, 2010 AT 5:22 AM

4 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
The only thing I can think of that makes a hissing sound is a vacuum leak. Have you checked hoses running to the rear?
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Thursday, August 12th, 2010 AT 4:01 PM
Tiny
MERLIN2021
  • EXPERT
This van has two evaporator cores, the rear core may now be leaking.
REAR AUXILIARY UNIT Rear auxiliary unit is an A/C-heater assembly which operates in conjunction with front A/C unit. Rear unit contains a separate blower motor, evaporator core, expansion valve and heater core separate from the front A/C-heater assembly. Blower motor draws in air through air intake grille on rear panel. Blower motor pushes air through evaporator or heater core as directed by mode door actuators. Rear auxiliary unit controls can be operated separately or in conjunction with master control switch at front A/C-heater control panel. Rear auxiliary unit controls can be set to operate blower at high or low speed in either A/C or HEAT mode.
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Thursday, August 12th, 2010 AT 4:01 PM
Tiny
KILROY0097
  • MEMBER
I don't know of a good way to check where the leak is coming from for certain without the necessary tools. However I had come to a similar conclusion while looking at my Chilton book for my van. So I'll take that back panel off and see about getting some eyeballs on that evaporator and see if it was as corroded as the one in the dash. I guess if it's in decent shape I may need to go to a place and have them dye/sniff the leak out before I can see about fixing it.

As for the vacuum leak from the hoses I wouldn't have a way to check since I would have to hook the system up to reacquire pump and the metal lines I think run under the car. Not sure though. So this may be something I won't be able to do until I have the leak location.

Thanks for the confirmations.
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Friday, August 13th, 2010 AT 7:45 AM
Tiny
MERLIN2021
  • EXPERT
Maybe you can go to Autozone and get the electronic sniffer(leak detector) under their loaner program.
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Friday, August 13th, 2010 AT 7:59 AM

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