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Thread: Weak AC 1989 Chevy with new blower motor.

  1. #1
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    Weak AC 1989 Chevy with new blower motor.

    The AC in my 89 2500 blows out very weak. I just put in the motor about 3 days ago and you can hear it running strong but you can barely feel the air coming out the vents. Does anyone know why this would be happening or what I can do to fix it?

  2. #2
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    mudseeker's Avatar
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    critters build a nest in the dash???
    blend doors?

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    I don't think I have a nest in my dash lol. What do you mean blend doors?

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    Senior Member chengny's Avatar
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    I'm not sure but there should be a blower motor resistor bank somewhere. Look for a plug type connector that is attached to the ducting on the engine side of the firewall. Make sure that is firmly seated.

    And make sure you have a strong connection to ground. Don't use the fan housing - it is plastic.

    To test the fan (and by-pass the resistors), establish a good ground and run a jumper from the positive terminal on your battery. The fan will see a full 12VDC as if you had your dash switch on high.

    If it is still sluggish, pull it and test it again using two jumpers from the battery. If it works correctly, you are not grounded properly. If it is still slow go get another fan.
    1986 Sierra Classic
    Lost it in a fire

    Replaced with 1986 Sierra K3500 single axle

  5. #5
    Senior Member chengny's Avatar
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    Blend door is that flap in the left hand section.
    1986 Sierra Classic
    Lost it in a fire

    Replaced with 1986 Sierra K3500 single axle

  6. #6
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    Quote Originally Posted by chengny View Post
    Blend door is that flap in the left hand section.
    Thinking that too, since hears the blower run strong.
    Sounds like blocked duct one way or another.
    Hear anything when changing air flow controls ?
    Please don't PM truck fix questions, bravely start a new thread for them. It is a forum afterall.

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    another possability is the Squirel cage that ataches to the motor could be stripped and or the fins broken.

  8. #8
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    Geez do you think positive, he just put that in
    Please don't PM truck fix questions, bravely start a new thread for them. It is a forum afterall.

  9. #9
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    Quote Originally Posted by crabtruck View Post
    Geez do you think positive, he just put that in
    lol Well no offense to the OP but you never know.

  10. #10
    Senior Member chengny's Avatar
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    Is this lack of flow only occuring when in the A/C mode?

    But first a question if I may - why did you install a new fan? Was the old one broken? Was there even a fan in the system?

    Anyway back to the "only when in A/C" part. This gets kinda involved and is counter-intuitive, so skip to the end if you want. If an evaporator coil is starved for refrigerant (AKA "needs a charge") it will not develop the proper degree of superheat and will be too cold by the time it is near the end of the loops in the coil. So an under-charged (under the right conditions) system will actually be colder than a properly charged one at the exit of the evap coil. This does not usually present a problem unless the refrigerant is so cold as to cause the coil the frost up. As the frost develops it begins to bridge the fins. As the flow of cabin air slows due to this restriction even less superheat is developed. At some point the coils and fins can become a block of ice.

    Usually there is enough leakage from the hot side of the blend door to prevent this. Try switching to heat for awhile and look underneath the truck. You may see a steady stream of water coming out of the drain hole instead of the usual dripping that you get when running A/C in humid conditions. When the coils have been defrosted, put it back to A/C and note the air flow. If it starts off heavy and then slows down that indicates that you are frosting up.

    To remedy this, add tiny shots of 134a. You should see the frost on the section of tubing between the orifice and the casing quickly melt away. When the tubing is frost free - STOP ADDING 134a. Drive around for a day or two and see if the sytem performs as designed. When it comes to charging an A/C system too much refrigerant is just as bad as too little. The pressure on both sides of the orifice/TXV reaches equilbrium and nothing flows. But that is another story...
    1986 Sierra Classic
    Lost it in a fire

    Replaced with 1986 Sierra K3500 single axle

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