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Thread: A/C pressure test is done at what "specified RPM?"

  1. #1
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    A/C pressure test is done at what "specified RPM?"

    I have gone through the shop manual and can't find the specified RPM at which to check the high and low pressures on the A/C. I see the temperature chart. The instructions on page N:06:01 look like the pressure check is at idle speed because it says "Start engine," but in trouble shooting it says "run engine at specified RPM." I can't find a "specified RPM" anywhere. Some of the generic YouTube videos say 2000RPM, but is that correct for the DMC?

    Thanks

  2. #2
    Motors about after dark Michael's Avatar
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    I don't think any specific RPM is necessary to check pressures. The pressures will be the same albeit the speed at which the compressor builds pressure will be increased with RPM and the cycling rate and cooling efficiency will also be slightly improved.

    If I am trying to set the low pressure cut off point, I usually will bump the RPM's to aid for time's sake and if I am trying to figure out or diagnose something, I may use a higher RPM to simulate driving conditions.

    I could be wrong but I don't remember any specific RPM needed for checking the manifold gauges.
    Last edited by Michael; 09-02-2021 at 11:31 PM.
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  3. #3
    Administrator Ron's Avatar
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    Yeah, it really doesn't matter because, as the chart notes, the readings are "to be taken when the clutch cuts out". It will be freewheeling...

  4. #4
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    "ambient temperature"

    Quote Originally Posted by A2lincoln View Post
    I have gone through the shop manual and can't find the specified RPM at which to check the high and low pressures on the A/C. I see the temperature chart. The instructions on page N:06:01 look like the pressure check is at idle speed because it says "Start engine," but in trouble shooting it says "run engine at specified RPM." I can't find a "specified RPM" anywhere. Some of the generic YouTube videos say 2000RPM, but is that correct for the DMC?

    Thanks
    Thank you for the responses. That makes sense.

    About the "ambient temperature" to use on the pressure charts - I've been using air temperature in the shade near the car. One article says take the temperature in the engine compartment, another said take the temperature two feet in front of the condenser, another said something about adding 40 degrees to the general air temperature.

    Any recommendations? I also understand that humidity should be take into consideration, but the DeLorean manual doesn't mention it.

  5. #5
    Motors about after dark Michael's Avatar
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    Quote Originally Posted by A2lincoln View Post
    Thank you for the responses. That makes sense.

    About the "ambient temperature" to use on the pressure charts - I've been using air temperature in the shade near the car. One article says take the temperature in the engine compartment, another said take the temperature two feet in front of the condenser, another said something about adding 40 degrees to the general air temperature.

    Any recommendations? I also understand that humidity should be take into consideration, but the DeLorean manual doesn't mention it.
    It's hard to do ambient temp because the car needs to be moving for the AC to really be efficient. Don't read the engine compartment...that info was probably for a front engine vehicle which would still be wrong but nonetheless I would say in front of the condenser. Keep on mind without airflow over the condenser and all the built up heat from an idling engine surrounding the car (in a garage I presume), you are still not getting a true reading. The air temps are just a ballpark frame of reference. Don't put a lot of emphasis on them.
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  6. #6
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    ambient temperature

    Quote Originally Posted by Michael View Post
    It's hard to do ambient temp because the car needs to be moving for the AC to really be efficient. Don't read the engine compartment...that info was probably for a front engine vehicle which would still be wrong but nonetheless I would say in front of the condenser. Keep on mind without airflow over the condenser and all the built up heat from an idling engine surrounding the car (in a garage I presume), you are still not getting a true reading. The air temps are just a ballpark frame of reference. Don't put a lot of emphasis on them.
    Thank you Michael.

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