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Thread: No AC

  1. #81
    Senior Member Trstno1's Avatar
    Join Date:  Aug 2014

    Location:  Anchorage, Alaska

    Posts:    694

    My VIN:    5625

    Ok. The system was low of 134a. I topped it off and ac works great now. I’ll have to track that leak down this winter. Now I notice that when at idle when the ac compressor kicks on my engine bogs down to about 550 rpm and acts like it wants to die. When the compressor is off the world is right again and I get my 750 rpm. First, shouldn’t the car compensate for the extra load of the compressor without killing idle rpm like that? 2nd - I am running Oem cooling fans and understand the extra load on the electrical system could be partially at fault. What do you think I can do in order to use the ac without worrying about the engine dying at a stop light? Is the idle control valve a potential culprit?

    Thanks in advance for your opinions.
    You can't buy happiness, but you can buy a DeLorean and that's sort of the same thing....

  2. #82
    Administrator Ron's Avatar
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    Quote Originally Posted by Trstno1 View Post
    First, shouldn’t the car compensate for the extra load of the compressor without killing idle rpm like that?
    Yes.

    Quote Originally Posted by Trstno1 View Post
    2nd - I am running Oem cooling fans and understand the extra load on the electrical system could be partially at fault.
    No, the fan's load on the electrical system only causes the alternator to kick in (if it isn't already). The alternator will then add a load to the engine, but the idle speed control system compensates for it. It should settle down at 775 ± 50 RPM, quickly.

    Quote Originally Posted by Trstno1 View Post
    What do you think I can do in order to use the ac without worrying about the engine dying at a stop light?
    - Check that the idle speed microswitch is working properly.
    Prop the throttle open slightly (steady) enough to disengage the microswitch. Then using a small screwdriver, listen for the RPM to change when you push/release the microswitch. If it does, make sure that the set screw is pressing the switch at idle, especially when you ease off the throttle (sticky linkage). If there is no change, check the microswitch and its wiring to the idle speed ECU with a meter (several threads on that here).

    - Feel the idle control valve (or "idle speed motor") to see if it is buzzing at idle.
    Wash it out thoroughly.

    - If the above doesn't help, borrow an idle speed ECU and swap yours out to eliminate it as the culprit.

    - Report back with what you find...


    (If you need either, I happen to have an ECU and microswitch up for sale HERE ;-)

  3. #83
    Senior Member Trstno1's Avatar
    Join Date:  Aug 2014

    Location:  Anchorage, Alaska

    Posts:    694

    My VIN:    5625

    Quote Originally Posted by Ron View Post
    Yes.

    No, the fan's load on the electrical system only causes the alternator to kick in (if it isn't already). The alternator will then add a load to the engine, but the idle speed control system compensates for it. It should settle down at 775 ± 50 RPM, quickly.

    - Check that the idle speed microswitch is working properly.
    Prop the throttle open slightly (steady) enough to disengage the microswitch. Then using a small screwdriver, listen for the RPM to change when you push/release the microswitch. If it does, make sure that the set screw is pressing the switch at idle, especially when you ease off the throttle (sticky linkage). If there is no change, check the microswitch and its wiring to the idle speed ECU with a meter (several threads on that here).

    - Feel the idle control valve (or "idle speed motor") to see if it is buzzing at idle.
    Wash it out thoroughly.

    - If the above doesn't help, borrow an idle speed ECU and swap yours out to eliminate it as the culprit.

    - Report back with what you find...


    (If you need either, I happen to have an ECU and microswitch up for sale HERE ;-)
    Ok - yes the idle speed micro switch is working. Yes the idle speed motor buzzes and closes with the ignition on. I will swap the idle ECU when I get the chance but really don’t think its the culprit. When the AC is turned on, what tells the idle ECU to raise the RPM to compensate for the AC compressor?
    You can't buy happiness, but you can buy a DeLorean and that's sort of the same thing....

  4. #84
    Administrator Ron's Avatar
    Join Date:  Jun 2011

    Location:  North GA

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    Quote Originally Posted by Trstno1 View Post
    Ok - yes the idle speed micro switch is working. Yes the idle speed motor buzzes and closes with the ignition on. I will swap the idle ECU when I get the chance but really don’t think its the culprit. When the AC is turned on, what tells the idle ECU to raise the RPM to compensate for the AC compressor?
    It sounds like they all might be ok.
    If the micro switch is closed and you turn on the AC (or load down the engine in any other way), the ECU sees the drop in RPM and tells the idle speed motor to add more air to the air/fuel mixture, causing the fuel control system to add more fuel (because it is lean), which causes the rise in RPM.

    ...I'm wondering if you might have a vacuum leak only when the AC is on. Maybe try plugging the vacuum feed port on the back of the air horns and then try it.

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