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Is an ac compressor supposed to be able to spin with the engine off?

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  • Is an ac compressor supposed to be able to spin with the engine off?

    Hi All, we have a 2004 Ford Freestar (3.9L with rear ac controls) and the ac went out over a year ago. The tech at the ac place we just took it to at first said there wasn't anything wrong with the compressor and then said there was, The tech said the compressor spins freely and there is no resistance when he spun the pulley with the engine off? I know that if an ac compressor won't spin at all that it is locked up, and that is bad, but I thought the ac compressor was supposed to spin when not on/under load. He told us that the best case scenario is 700 bucks for a new compressor/1400 to 1700 if he has to basically replace everything. We are seniors on a fixed income and don't have that kind of money. Does this sound right?

  • #2
    Your post is a little confusing to me. The AC compressor clutch has a free-spinning outer pulley. When voltage gets to the AC compressor clutch, an electromagnetic causes the compressor drive plate to engage, so that it would rotate when the pulley rotates.

    Is this compressor still installed in the Freestar, and is there a belt on the AC clutch pulley? If so, with the engine off, the nut/bolt in the center of the drive plate should be able to be rotated clockwise with a wrench, sometimes by hand, and there should be a fair amount of physical resistance.

    If the compressor has been removed from the Freestar, the nut/bolt in the center of the drive plate should be able to be rotated clockwise with a wrench, sometimes by hand, and there should be a fair amount of physical resistance, and the outer pulley should spin freely and practically silently.

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    • #3
      Well, the pulley itself shouldn't have any resistance when the clutch is not energized. It turns all the time the belt turn. The front of the pulley is covered by the clutch face which is attached to the compressor shaft. When the system is empty and a vacuum pulled on the system, the resistance to turn that shaft is low, I could turn it with one finger. When the system is charged, it still doesn't take much to turn it slowly, but there will be a building resistance the faster you try and turn it.
      Your mechanic couldn't turn the pulley with the belt in place, so I'm guessing he was turning the shaft. It comes down to do you trust the person your are dealing with or not, if you have a doubt seek a 2nd opinion.
      Last edited by Cornbinder89; 1 week ago.

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      • #4
        Thanks all, and sorry for not giving more info. The ac compressor was in the car, all belts on. We had just pulled in to the place. I could not see what the guy was doing from where I was standing. The ac tech said the compressor has a shaft inside and the way it was spinning, without any compression, caused him to believe the compressor was bad. Because the compressor was 'bad', he said he didn't know if any metal pieces had gone through the system. Because of the Freestar van's engine compartment layout, he said he couldn't easily get to the orifice to check so he didn't know if it would be just a compressor replacement or an entire system replaced. Hope this helps.

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        • #5
          oldpops: I'm here too and you had about same thoughts from the other site. If you want concurrence - I don't blame you. These guys are just as qualified. I only will say on this, here that the web to tell you what to do is limited. At some point if and when you trust the shop and tech set them free to do it.

          Nothing more I can add here in person is always the best at some point you have to trust shops to do the right thing by you,
          Tom
          MetroWest, Boston

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          • #6
            Originally posted by Cusser View Post
            Your post is a little confusing to me. The AC compressor clutch has a free-spinning outer pulley. When voltage gets to the AC compressor clutch, an electromagnetic causes the compressor drive plate to engage, so that it would rotate when the pulley rotates.

            Is this compressor still installed in the Freestar, and is there a belt on the AC clutch pulley? If so, with the engine off, the nut/bolt in the center of the drive plate should be able to be rotated clockwise with a wrench, sometimes by hand, and there should be a fair amount of physical resistance.

            If the compressor has been removed from the Freestar, the nut/bolt in the center of the drive plate should be able to be rotated clockwise with a wrench, sometimes by hand, and there should be a fair amount of physical resistance, and the outer pulley should spin freely and practically silently.
            So compressor is still installed. So do this test yourself: with the engine off, the nut/bolt in the center of the drive plate should be able to be rotated clockwise with a wrench, sometimes by hand, and there should be a fair amount of physical resistance.

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            • #7
              If I'm Not mistaken, some Fords used a scroll type compressor, these will have less drag at slow rotation than a piston type compressor. I wouldn't call the compressor bad without looking at pressures with a changed system and the clutch pulled in.

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