Troubleshooting An A/C Recirc Door Vacuum Problem

Discussion in '2nd Gen - 2003 - 2006' started by dlyoung1, Aug 13, 2019.

  1. dlyoung1

    dlyoung1 Member

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    Need some guidance on where to start looking for a vacuum problem. This is my starting point:

    2003 Expy, standard climate system (NO EATC)

    A/C will work fine in "Regular" a/c mode (at least getting as cool as it can in town with outside air in 103 Texas heat). "MAX (recirc) mode works only at idle. As soon as I step on the gas and the RPM start climbing, the dash vents slowly shut down and I can feel the air shift to the DEFROST vents. Back to idle (at a stop light) and it shifts right back to dash vents.

    Since it is RPM relative and the vents shift to the "default" position at DEFROST, I am obviously thinking a vacuum problem somewhere between the a/c control unit and the Recirc Door Vacuum Motor? Don't want to go tearing into the dash and the a/c control unit before I rule out a vac leak under the hood or under the dash. Can't seem to find a definitive vacuum "map" to trace the vac line back thru the firewall to its source. Where would you start the troubleshoot?
     
  2. dlyoung1

    dlyoung1 Member

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    Update:
    Believe I've found the vac line running across the top of the firewall with a tee fitting feeding a very small diameter vac line that goes through the firewall high on the passenger side.That line goes around the back of the battery to the small vac reservoir canister? I'll give that entire line a good inspection first thing in the AM (when it's NOT 110 on the driveway).
     
  3. Hamfisted

    Hamfisted Full Access Members

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    Yes, those lines are susceptible to leaks cause by heat and deterioration of the rubber. They actually sell that whole line assembly over at Rock Auto if you find it un-repairable. You should see two lines passing through the firewall grommet. The bare tube is the supply line that comes off the intake manifold and goes to the dash control module, the line that has the shroud around it goes up to the hot water control valve there above the passenger side valve cover area. A lot of times that tube gets knocked off the hot water control valve when somebody works on the sparkplugs on that side. If it is off the hot water valve you will lose your dash vent controls.


    Vacuum tubes passing through the firewall grommet .....

    [​IMG]



    [​IMG]




    Replacement vacuum tubing from Rock Auto ....
    https://www.rockauto.com/en/catalog...1119,heat+&+air+conditioning,vacuum+hose,6908

    [​IMG]
     
  4. dlyoung1

    dlyoung1 Member

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    Damn, Ham, that is what I call a full-service reply! Not just anyone goes ahead and looks up the parts I might need. Thanks!

    Now, a clarifying question. I have good vent selection function at the dash controller (REG a/c, heat, defrost, etc. and temp/blend door), with the MAX a/c recirc door apparently losing sufficient vac to hold it open when the engine RPM rises. So, I'm getting vac to the controller and out to the Recirc Door actuator/motor. Seems to me the leak would be in that portion of the vac line? Where is that actuator actually located? The diagram I found online gives no info as to physical location of the components.
     
  5. Hamfisted

    Hamfisted Full Access Members

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    Much more likely you have a vacuum leak under the hood ....
     
  6. dlyoung1

    dlyoung1 Member

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    Update to the update:

    Progress made, although not 100%. I did a thorough visual on that vac line and snugged up all the fittings. Pulled the small canister from the fender behind the battery and the connection to that canister may have been a bit loose. I put it all back together and gave it a drive. Improvement in that the "vent shift" from dash to defrost (while on MAX a/c only) was not as pronounced and only happened under acceleration. Soon as you get to a cruising RPM, it returns to the dash vents. I think the wife can work with that for now. I guess the next step would be to inspect everything behind the a/c controller and the vac line that feeds the recirc door motor?
     

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