Results 1 to 4 of 4

Thread: 94 SC A/C Blend Door Issue

  1. #1
    Join Date
    Jun 2003
    Location
    Concord, NC
    Posts
    107

    94 SC A/C Blend Door Issue

    Under acceleration (not WOT), all air output into the cabin diverts to the Defrost vents.

    I checked the following with a Mighty-Vac:

    1. A/C Vacuum Reservoir behind fender splash panel of Right Front Fender
    2. Vacuum Line with Check valve running from reservoir to Vacuum Tee at Firewall
    3. Vacuum Tee at Firewall
    4. Vacuum Line running from Vacuum Tee at Firewall to Intake Manifold


    All of these items held vacuum. However, when I connect the Mighty-Vac to the vacuum line that goes from the vacuum tee at the firewall into the passenger cabin (presumably to a component that controls the blend doors), I cannot create a vacuum with the Mighty Vac. I don't know that this necessarily indicates an issue.

    Does anyone have any other ideas regarding items to check and where and how I might access them? At the moment I can't say for certain if this only happens when in A/C mode or also when just utilizing panel vents and/or heat. I am currently replacing tension strut bushings. Once I complete those I will verify vent behavior without A/C turned on.

    Best Regards,

    Ted

  2. #2
    Join Date
    Apr 2002
    Location
    Lakeville, MN
    Posts
    13,517
    Are you making boost when accelerating? If you make boost, you don't make vacuum thus the A/C system goes to fail safe mode which means up to defrost.

    Do you notice a loss of brake assist? I'd check the brake pedal while accelerating to see if you lost that as well.

    Unless you're on a slow accelerate down a long road, you shouldn't normally be able to cause all the vac to leave the system. There are Vac reservoir in the A/C system and brakes. The HVAC reservoir could be bad, or you may have a vacuum leak somewhere that is never allowing all these systems to gain enough vac.

  3. #3
    Join Date
    Feb 2006
    Posts
    1,964
    I would check all of the vacuum motors under the dash, specifically the one on the passenger side below the glovebox to make sure they are all connected.

  4. #4
    Join Date
    Jun 2003
    Location
    Concord, NC
    Posts
    107
    Thanks for the replies. bird4us nailed it! The problem was indeed a loose vacuum line going to the vacuum motor in the passenger side footwell.

    This had happened one other time before, but it had been so many years ago I had forgotten all about that vacuum motor.

    Thanks again for the assistance!

    Best Regards,

    Ted

Similar Threads

  1. more A/C questions ...
    By tcshum in forum Technical Forum
    Replies: 6
    Last Post: 05-24-2005, 07:57 PM
  2. a/c causing idle to drop
    By supercharged in forum Technical Forum
    Replies: 3
    Last Post: 01-16-2003, 11:42 PM
  3. Car surges with A/C on
    By Dale Puumala in forum Technical Forum
    Replies: 1
    Last Post: 07-02-2002, 03:03 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •