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Thread: Refurbing a Very Early A/C System

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  1. #1
    Senior Member DMC-81's Avatar
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    Refurbing a Very Early A/C System

    Hi there,

    I am in the process of refurbishing my "very early" A/C system, and I thought I'd document my adventure and what I learned in this thread.

    The current state of my system is:

    - Completely original
    - The OEM Sankyo SD510 compressor engages when manually tripped
    - The refrigerant is R12
    - The system seems tight and is holding refrigerant, but the amount is unknown

    At one point, it cooled briefly, but then stopped cooling and the compressor is not building pressure. After some troubleshooting, I suspect a blockage, but it could also be a compressor failure. I have a primary plan and back up plan to get the system operating again.

    My Primary goal is to:
    Refurbish my original compressor
    Maintain the early style accumulator configuration
    Keep the system on R12
    Add the high pressure switch and pressure release valve that is missing on my system

    And if that doesn't work out, my back up plan is to:
    Replace the compressor
    Convert to the later style accumulator
    Convert to R134a

    Here are some pictures:

    Compressor:
    image.jpg

    Early Accumulator 100743, without the cross on the crossover hose:
    image.jpg

    Lower condenser hose without the later condenser adapter:
    image.jpg

    My first step is to pull vacuum on the system before dismantling it to double check for a small leak...
    Dana

    1981 DeLorean DMC-12 (5 Speed, Gas Flap, Black Interior, Windshield Antenna, Dark Gray)
    Restored as "mostly correct, but with flaws corrected". Pictures and comments of my restoration are in the albums section on my profile.
    1985 Chevrolet Corvette, Z51, 4+3 manual
    2006 Dodge Magnum R/T (D/D)
    2010 Camaro SS (Transformers Edition)

  2. #2
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    Best advice would be to go to an A/C shop and have them check it out.
    David Teitelbaum

  3. #3
    Senior Member DMC-81's Avatar
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    Quote Originally Posted by David T View Post
    Best advice would be to go to an A/C shop and have them check it out.
    Thanks. I got advice from a few shops and the consensus is that the system needs a repair/rebuild.

    ---------------------------------------

    Yesterday morning I attached my gauges and a pump and vacuumed down the empty system. It achieved 60hg quite quickly. I read in a few places to go down to 20-30 so I didn't want to go any further. So I closed the low pressure valve and shut off the pump.

    image.jpg

    Initial reading:
    image.jpg

    I checked the gauges every hour or so and up to 12 hours later, it was still on 60hg. 24 hours later, the reading was 55 -57 hg:
    image.jpg

    What do you all think? Is this defined as a tight system, or do I have a very slow leak? I suppose the fact that it had gauges attached could introduce leak points. The car was not registered for 14 years before I got it yet it still had refrigerant in the system.
    Dana

    1981 DeLorean DMC-12 (5 Speed, Gas Flap, Black Interior, Windshield Antenna, Dark Gray)
    Restored as "mostly correct, but with flaws corrected". Pictures and comments of my restoration are in the albums section on my profile.
    1985 Chevrolet Corvette, Z51, 4+3 manual
    2006 Dodge Magnum R/T (D/D)
    2010 Camaro SS (Transformers Edition)

  4. #4
    Senior Member Bitsyncmaster's Avatar
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    It seems pretty good. Using vacuum is not a perfect test but a good ball park. It's best to change the service valves anyway since those tend to leak with age. You want to pull a good vacuum when your ready to charge. Best to run the vacuum pump for at lease one hour. Then purge the fill hose running a little refrigerant through the open hose end.
    Dave M vin 03572
    http://dm-eng.weebly.com/

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    Senior Member DMC-81's Avatar
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    Quote Originally Posted by Bitsyncmaster View Post
    It seems pretty good. Using vacuum is not a perfect test but a good ball park. It's best to change the service valves anyway since those tend to leak with age. You want to pull a good vacuum when your ready to charge. Best to run the vacuum pump for at lease one hour. Then purge the fill hose running a little refrigerant through the open hose end.
    Great. Thanks Dave.
    Dana

    1981 DeLorean DMC-12 (5 Speed, Gas Flap, Black Interior, Windshield Antenna, Dark Gray)
    Restored as "mostly correct, but with flaws corrected". Pictures and comments of my restoration are in the albums section on my profile.
    1985 Chevrolet Corvette, Z51, 4+3 manual
    2006 Dodge Magnum R/T (D/D)
    2010 Camaro SS (Transformers Edition)

  6. #6
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    Hard to really test for leaks with vacuum. Since atmosphere is 15 psi the most you can go is negative 15 psi or 30" of vacuum. And all you can tell is if it leaks or not, you cannot find a leak that way. A good shop will pressurize the system to 100 psi with Nitrogen and then use a leaktest solution (soapy water and Glycerine) and spray it at the joints to check for bubbles (leaks). Since you are trying to "do it on the cheap" drain the oil out of the compressor and refill with fresh. Change the valve cores. Pressurize with dry shop air to 100 psi and check for leaks at every joint. Fix any leaks and evacuate again for at least 1 hour and then refill with R-12. The longer the vacuum the better, you are trying to evaporate (boil) any moisture out that is in the system, not just suck out all of the air. It takes some time. To speed it up you can use a heat gun on the accumulator to dry out the desiccant. If the hoses are original you really should replace them and the accumulator.
    David Teitelbaum

  7. #7
    Senior Member DMC5180's Avatar
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    Refurbing a Very Early A/C System

    The puzzler here is that it didn't build system pressure. Because it is closed loop, any blockage/restriction should cause the Highside to climb like crazy.

    Broken reed valves would cause no pressure to build. But from your teardown inspection all the components appear to be good.

    Fwiw, when you reassemble the clutch, be sure the air gap is within spec.
    .016"-.031". Adjust or remove shims as needed to bring into spec. When I was redoing my system last year, I noticed the clutch was slipping intermittently. The Clutch Air gap was almost .060. Since I was replacing the compressor anyway with an SD7H15, it didn't matter to me. For comparison the New compressor's clutch was near the bottom of the spec.
    Last edited by DMC5180; 09-24-2017 at 04:06 PM.
    DENNIS

    VIN 5180, Frame 3652, STAGE II​, DM-eng Solid State Solutions (RPM Rly, Dm.Lt.Mod., Fan Fail Mod. , FAN Rly, HS.Rly) , HID headlights, SPAX user since 2009, Eibach springs, M Adj. Rear LCA's, DPNW poly-sway bar kit, DMCEU LCA Stabilizer link kit, DMCMW Illuminated door sills, Aussie Illuminated SS Shifter plate, REAL MOMO EVO Steering wheel, DELOREANA Extended View Side Mirrors w/ Heaters, DELOREANA LED Door Lights.

  8. #8
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    You can tell if the compressor is turning by observing the clutch. I worked on one car, the clutch would engage fine but once it let go, it could not re-engage the clutch again. Checked the gap and it was way too big. Removed some shims and it was fine. Yes, if it is turning you should see some pressure differential between the high and low sides if it is working. When you don't see any action you check the oil for metal and when you tear it down you should have found *something* not right. Are you sure your test lines depressed the service valves and your manifold gauge works? When I do something and doesn't seem to make sense I recheck what I did to make sure I didn't do anything wrong.
    David Teitelbaum

  9. #9
    Senior Member DMC5180's Avatar
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    Quote Originally Posted by David T View Post
    Are you sure your test lines depressed the service valves and your manifold gauge works? When I do something and doesn't seem to make sense I recheck what I did to make sure I didn't do anything wrong.
    Back in post #3 it says the vacuum pulled down to 60hg quite quickly.

    Btw, thats a cmHg scale. Normally it would be INHg
    30-31 inhg would be normal full vacuum.

    Which makes me think that the gauge valves might not be open.
    DENNIS

    VIN 5180, Frame 3652, STAGE II​, DM-eng Solid State Solutions (RPM Rly, Dm.Lt.Mod., Fan Fail Mod. , FAN Rly, HS.Rly) , HID headlights, SPAX user since 2009, Eibach springs, M Adj. Rear LCA's, DPNW poly-sway bar kit, DMCEU LCA Stabilizer link kit, DMCMW Illuminated door sills, Aussie Illuminated SS Shifter plate, REAL MOMO EVO Steering wheel, DELOREANA Extended View Side Mirrors w/ Heaters, DELOREANA LED Door Lights.

  10. #10
    Senior Member DMC-81's Avatar
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    Quote Originally Posted by NckT View Post
    Good work there Dana, keep it up

    I'd recommend to soak any O rings in air con mineral oil overnight before fitting to aid sealing.
    Thanks! I'll do that.

    Quote Originally Posted by DMC5180 View Post
    The puzzler here is that it didn't build system pressure. Because it is closed loop, any blockage/restriction should cause the Highside to climb like crazy.

    Broken reed valves would cause no pressure to build. But from your teardown inspection all the components appear to be good.

    Fwiw, when you reassemble the clutch, be sure the air gap is within spec.
    .016"-.031". Adjust or remove shims as needed to bring into spec. When I was redoing my system last year, I noticed the clutch was slipping intermittently. The Clutch Air gap was almost .060. Since I was replacing the compressor anyway with an SD7H15, it didn't matter to me. For comparison the New compressor's clutch was near the bottom of the spec.
    Yeah, I expected a failed compressor or a plugged orfice tube, but I have yet to check the evaporator and condenser. Thanks for the air gap specs, I'll be sure to check it during assembly. I checked that during evaluation before disassembly and it was within spec.


    Quote Originally Posted by DMC5180 View Post
    Back in post #3 it says the vacuum pulled down to 60hg quite quickly.

    Btw, thats a cmHg scale. Normally it would be INHg
    30-31 inhg would be normal full vacuum.

    Which makes me think that the gauge valves might not be open.
    Correct, but I tested the system 3 times before teardown and the high side gauge:
    - needed to be purged
    - showed readings all 3 times (and some mild fluctuations)
    - and went negative during vacuuming.
    If either side was not connected, I would expect a zero reading, right?

    Good discussion.

    Regardless, I'm in the refurbishment process now, which I needed to do anyway to replace the seals, orifice tube and accumulator.
    Dana

    1981 DeLorean DMC-12 (5 Speed, Gas Flap, Black Interior, Windshield Antenna, Dark Gray)
    Restored as "mostly correct, but with flaws corrected". Pictures and comments of my restoration are in the albums section on my profile.
    1985 Chevrolet Corvette, Z51, 4+3 manual
    2006 Dodge Magnum R/T (D/D)
    2010 Camaro SS (Transformers Edition)

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