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I have an 04 SC with 170K miles. Problem - Whenever I turn on the AC no air comes out of the center dash vents, but instead comes out of the defrost at the base of the windshield. I am getting air out of the outside vents, but none from the center vents. Also, same for the heater. No warm air in the foot wells, only from the defrost vents.
I have used the Automatic setting, as well as setting the mode manually. I have verified that the vents are in fact open. Same results.
If anyone has experienced a similar issue would appreciate some feedback on possible solution. A direct reply to rediamond@bellsouth.net is okay.
The automatic climate control system works primarily using 4 electric servo motors that control how the hvac performs. These servos are a fairly simple technology that is long outdated, and can be very frustrating for anyone who owns a vehicle from this era with the climate control. The servos cost from $100-$150 for new OEM replacements, and they can be a little tedious to remove and replace them. The good news is that they can be replaced by anyone who is willing to crawl under the dash and battle with them. They will just be her in place by 4 bolts each. Then they can be opened up, cleaned, greased and reinstalled and often they will work great for another 100k or more. Not always, but plenty of other owners will confirm that they solved this problem with just their time and patience. There is 1 under the drivers side and 3 under the passenger side. Make sure to mark the position of each arm before opening it up so you return it to the same place before reinstalling. I would suggest you do one side at a time, remove each servo in the obvious order, they are can of stack on each other so you have to remove them all at the same time, when you open them up, you’ll find a set of electronic terminals that ride on a circuit board these needs to be carefully cleaned with isopropyl alcohol and some q tips then grease the gears with some dielectric grease or some of the extra grease built up on the inside. You’ll want to plug them in and then cycle the hvac controller to ensure that each one is fully functioning before reinstalling it. If you have any that don’t function or they are noisy, then you can find a used one or remanufactured one for much less than OEM. But you might need to replace it much sooner than the OEM option. The servos are labeled 87106 C,D,H,J
in addition to the symptoms you’ve described, are you getting a buzzing or grinding noise when you turn on your fan? i tried cleaning and regreasing but it didn’t work for me. i ended up replacing with an after market servo from ebay. so far so good.
this thread has an excellent video showing how to change the mode servo, one of the four servos described above, as well as a pdf with steps to run diagnostic tests on the hvac system.
AC/Heater Vent Issues
