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Carhelp4u
Carhelp4u, ASE CERTIFIED TECH
Category: Car
Satisfied Customers: 5203
Experience:  ASE CERTIFICATION
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I have a 1999 Jimmy and the heater/AC control switch does not

Resolved Question:

I have a 1999 Jimmy and the heater/AC control switch does not act properly. I cannot get air to feed to the floor vent. If the contol is set on Vent it works properly. Setting it on defrost, it works properly. Setting it on any A/C control it works properly. However, when I select the floor mode, it blows through the defrost ducts.
Submitted: 5 years ago.
Category: Car
Expert:  Carhelp4u replied 5 years ago.
Do you have automatic climate control or manual control?
Customer: replied 5 years ago.
Manual control
Expert:  Carhelp4u replied 5 years ago.

Ok this system is controlled by vacuum. The most common failure on this model would be the dash mounted mode switch leaking vacuum from the floor setting selection. The first thing we need to do is verify that the mode actuator is not ruptured and that the mode door is working correctly. To access this valve, you will need to remove the trim underneath the steering column. At this point you should be able to see the actuator. What I would recommend is removing the actuator to verify proper movement of the door, and to check to see if there is any visible damage to the actuator. Here is how to access this point. Feel free to contact me with any questions! Good luck!

  • Remove the knee bolster.
    Object Number: 515031  Size: SH

  • Remove the right side driver knee bolster bracket (2) from the steering column bracket (1) and the intermediate bracket (3).
    Object Number: 394104  Size: SH

  • Disconnect the vacuum connectors (1) from the mode actuator (5).
  • Remove the actuator rod retaining clip (4).
  • Remove the actuator rod (2) from the mode valve lever (3).
    Object Number: 394087  Size: SH

  • Firmly pull on the mode actuator in order to remove the actuator from the heater/vent module.
  • Customer: replied 5 years ago.
    I won't have a chance to look at this until tomorrow. You're probably "right on" but I may have another question on verifying the proper operation of the actuator. I guess I can see if this is working once the lower panels are removed. Thanks for your rapid response.
    Expert:  Carhelp4u replied 5 years ago.
    Yes let me know when you get a chance! Thanks!
    Customer: replied 5 years ago.
    I worked on this today. Your instructions didn't tell me that I had to remove a metal shield around the transmission column and also, the lower center covering holding the power outlets so the actuator could be viewed.

    I tested the actuator and it would only attempt to move in one direction. There is a red and blue vacuum hose going to this control. I have vacuum on the red side but when I switch the manual control to floor mode, it still retains vacuum on the red side of the switch (however, just a little less as I put my finger over the vacuum hoses to feel the suction). It appears to be only working one way. I cannot feel any vacuum coming from the blue hose when I change mode selection. I also had a new mode actuator and the old and new one show the same symtoms.

    My only conclusion now is that the mode selector switch is bad. Comments?
    Expert:  Carhelp4u replied 5 years ago.
    I would agree with you. This does sound as though there is an issue with the actual vacuum switch. I am trying to locate a chart to see where vacuum should be at each setting. i want to be able to verify this for you, but I am not finding the chart I am looking for. I appologize for not sending the info on the plate under the steering column. I forgot that you had to remove that also. I will get back to you asap as I am looking for this vaccum diagram to verify if there should be vacuum at this point for sure.
    Expert:  Carhelp4u replied 5 years ago.

    Ok, I found it. My concern at this point is that we are even on the right actuator. The actuator with the blue and the red vacuum lines is the defroster actuator. The actuator in question should be the one with a yellow and a brown vacuum line. This would be the mode valve.


    Object Number: 619601  Size: MF

    (1)Recirculate Air Inlet Port
    (2)Heat Port
    (3)Heat Mode Port
    (4)A/C Mode Port (Vent Mode Port with RPO C42)
    (5)Defrost Port
    (6)Source Vacuum Port
    (7)Vacuum Hose - Blue
    (8)Recirculation Actuator
    (9)Vacuum Hose - Orange
    (10)Vacuum Source
    (11)Vacuum Hose - Black
    (12)Rotary Vacuum (Mode) Switch
    (13)Vacuum Hose - Yellow
    (14)Vacuum Hose - Gray
    (15)Heater Slave Valve Actuator
    (16)Mode Actuator
    (17)Vacuum Hose - Brown
    (18)Vacuum Hose - Red
    (19)Defroster Actuator

    Mode

    Port 1

    Port 2

    Port 3

    Port 4

    Port 5

    Port 6

    DEFINITION: This table shows the state of the vacuum supply at the vacuum ports shown in the Vacuum Routing Diagram for each mode switch position. The port numbers are located on the vacuum rotary (mode) switch.

    OFF

    VENT

    VAC

    VAC

    VENT

    VENT

    VAC

    MAX (C60)

    VAC

    VAC

    VENT

    VAC

    VENT

    VAC

    NORM (C60)

    VENT

    VAC

    VENT

    VAC

    VENT

    VAC

    BI-LEV

    VENT

    VAC

    VENT

    VENT

    VENT

    VAC

    VENT

    VENT

    VAC

    VENT

    VAC

    VENT

    VAC

    HTR

    VENT

    VAC

    VAC

    VENT

    VENT

    VAC

    BLEND

    VENT

    VENT

    VAC

    VENT

    VENT

    VAC

    DEF

    VENT

    VENT

    VAC

    VENT

    VAC

    VAC

    NOTE: No source vacuum, insufficient source vacuum, or an improperly routed vacuum supply will cause air delivery to be improper.

    Customer: replied 5 years ago.
    <p>Do you have any idea where I would find the actuator for the floor control? The one with the yellow and brown vacuum hoses.</p>
    Customer: replied 5 years ago.
    <p>I found the other actuator and it is working. It was located above the other and closer to the firewall. Just as a precaution I installed a new mode actuator on it that I had but the problem has not gone away.</p><p> </p><p>I'm at a total loss as to where the problem may reside.</p><p> </p><p>I watched both actuators work as I moved the mode selector switch. However, I can't tell if they're opening the correct way. But they are moving.</p><p> </p><p>Could it be something inside the heater box?</p><p> </p><p>I guess I'll just have to put up with heat coming through the upper vents.</p><p> </p><p>By the way, I'd like to strangle the engineer that designed this system where its almost impossible to work on.</p>
    Expert:  Carhelp4u replied 5 years ago.
    I understand your feelings on working at this point. You should see some of the things they are doing with the new models. Its scary for sure. If the engineers had to work on them, they would not be doing this type of stuff for sure. Anyway, do you have vacuum at the yellow vacuum line at this point?
    Customer: replied 5 years ago.
    I didn't actually check the yellow line for vaccuum, but the actuator does move back and forth so I'm assuming vacuum exists.
    Expert:  Carhelp4u replied 5 years ago.
    Well we really need to verify that there is vacuum at this point. If no vacuum exists, I would really start looking at the control switch as more of a problem.
    Carhelp4u, ASE CERTIFIED TECH
    Category: Car
    Satisfied Customers: 5203
    Experience: ASE CERTIFICATION
    Carhelp4u and 4 other Car Specialists are ready to help you
    Customer: replied 5 years ago.
    <p>Actually, I needed the car and put the dash back together. I don't have any more time to try and solve the problem.   Working on this over several days just got to be too much of a chore and very frustrating. I guess I'll live with heat only coming out of the dash.</p><p> </p><p>Thanks for your help and time. You tried.</p><p> </p><p>I'll accept the answer to finish our dialog.</p>

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