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Thread: A/C System Q's

  1. #1
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    A/C System Q's

    Does anybody know:

    1) What are the A/C's high and low pressure sides' readings.

    2) What A/C system oil is recommended for our Z's, i.e.: PAG-46?

    3) What is oil volume required to refill the A/C system?

    4) Does the system have an FOT? If so, where it might be located, and how often to replace?

    5) What the vacuum pressure should be, and for how long (before 134-a refill)?

    Thanx in advance for the time taken to review the inquiry above.

    M
    Last edited by dreamrider01; 06-10-2012 at 07:47 PM. Reason: Automerged Doublepost

  2. #2
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    1) What are the A/C's high and low pressure sides' readings.

    Depends on the temperatures. About 30-40 psi on the low side, about 180-220 on the high side for about 70-80 F ambient.

    2) What A/C system oil is recommended for our Z's, i.e.: PAG-46?

    No. PAG-100.

    3) What is oil volume required to refill the A/C system?

    Depends on what you remove. If it's the compressor only, measure what you pour out and replace that much, plus a tiny bit more. The entire system takes 6 oz.

    4) Does the system have an FOT? If so, where it might be located, and how often to replace?

    I don't know what an FOT is, so I guess I've never seen one on my Z3.

    5) What the should be, and for how long (before 134-a refill)?

    You don't really get to set a vacuum pressure. You use all the pump will provide. For a low-end pump, allow an hour or more. Really good pumps can be faster. You can't over-evacuate the system.
    Last edited by Blacklane; 06-10-2012 at 11:57 PM.

  3. #3
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    Quote Originally Posted by Blacklane View Post
    1) What are the A/C's high and low pressure sides' readings.

    Depends on the temperatures. About 30-40 psi on the low side, about 180-220 on the high side for about 70-80 F ambient.

    2) What A/C system oil is recommended for our Z's, i.e.: PAG-46?

    No. PAG-100.

    3) What is oil volume required to refill the A/C system?

    Depends on what you remove. If it's the compressor only, measure what you pour out and replace that much, plus a tiny bit more. The entire system takes 6 oz.

    4) Does the system have an FOT? If so, where it might be located, and how often to replace?

    I don't know what an FOT is, so I guess I've never seen one on my Z3.

    5) What the should be, and for how long (before 134-a refill)?

    You don't really get to set a vacuum pressure. You use all the pump will provide. For a low-end pump, allow an hour or more. Really good pumps can be faster. You can't over-evacuate the system.
    Very helpful, Blacklane. Thanx!

    FOT (Fixed Orifice Tube), or OT (Orifice Tube) is a in-line filter usually found on the low pressure side. Sometimes it is found in the connection after the drier and before the exchanger, or in the connection after the exchanger and before the compressor. But, in the Z who knows if it even has one. It is tough to find inside which connection if no guidance available. But... One way to find out...

    It can get gunked up, and decrease flow, hence efficiency of the system. It is usually a $2 part that can kill your compressor if plugged up.

    BTW, I have nothing to replace. I just want to do a system flush. I am doing the pre-vacuum minor drying with a second flush w/ pure denatured EtOH. My vacuum pump gets down to -30 psi. I think 1 hr will be enough.

    M
    Last edited by dreamrider01; 06-11-2012 at 01:02 AM.

  4. #4
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    Then no. The expansion valve does the job of a fixed-orifice tube. Given the huge variation in temperatures and compressor pressures, expansion valves are pretty much all you find on R-134a automotive systems.

    You might want to look around for the exact volume of oil required for a complete flush. One source I have says 6 oz. I believe the Bentley manual calls for 4.1 oz.

    BTW: Draining, flushing, and refilling an AC system as preventative maintenance is not really advisable. There is nothing in there that is "breaking down" and opening seals, adding solvents, etc. is not going to improve things. An exception might be if you think there is air in the system from some DIY refills, but that would be evident from the pressures and even then would only require a refrigerant drain and fill, not opening the system and not adding oil.
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    Last edited by Blacklane; 06-11-2012 at 12:47 PM.

  5. #5
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    Quote Originally Posted by Blacklane View Post
    Then no. The expansion valve does the job of a fixed-orifice tube. Given the huge variation in temperatures and compressor pressures, expansion valves are pretty much all you find on R-134a automotive systems.

    You might want to look around for the exact volume of oil required for a complete flush. One source I have says 6 oz. I believe the Bentley manual call for 4.1 oz.

    BTW: Draining, flushing, and refilling an AC system as preventative maintenance is not really advisable. There is nothing in there that is "breaking down" and opening seals, adding solvents, etc. is not going to improve things. An exception might be if you think there is air in the system from some DIY refills, but that would be evident from the pressures and even then would only require a refrigerant drain and fill, not opening the system and not adding oil.
    Again, thanx.

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