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Thread: AC Orifice Tube

  1. #11
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    Quote Originally Posted by Ron View Post
    Something don't sound right to me here??
    Using your numbers, you would be decreasing the orifice diameter which would mean the refrigerant would flow through slower. That would mean longer cycle times, which would increase high side pressure. I always heard that people used VOVs on a D to lower the pressure because 134a has higher pressure than R12 (for 70įF and greater, which I know is true). Seems you would be making a bad situation worse. What am I missing?
    The smaller diameter would make for higher "high side" pressures and lower "low side" pressures. But I would think it would make for shorter cycles because the low pressure switch would keep tripping. Not sure how it would effect on proformance.

    I will say that it's been my experince that converting r12 to 134a just never works as good. New cars are great, but the conversions suck. That's why I'm keeping mine R12.

  2. #12
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by 81dmc View Post
    I thought the same thing, but with an orifice tube being $3 and easy to replace, I’m up for an experiment.

    I’ve never had good ac performance in my car with all new components. I've tried everything but a different sized OT.
    +1

    I like owners experimenting. You never know what you find thinking outside the box.

    I never had good AC performance until I replaced the condensation drain with a real elbow. The stock drain is pinched and can not keep up with humidity. When your box fills with water the evaporator does not work well.
    Dave M vin 03572
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  3. #13
    Senior Member 81dmc's Avatar
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    Actually I take it back. First Iím trying the 1.7mm Blue Orifice Tube p/n 38621 from a 2004 Ford F-150. If itís not enough, then Iíll try the Red 1.6mm.


    Got too much to do with the car. Getting ahead of myself lol.
    VIN 831- Delorean.eu Roof Box, Double Din, Custom Instrument Cluster, QA1 Suspension.
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  4. #14
    Senior Member DMC-81's Avatar
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    Quote Originally Posted by Bitsyncmaster View Post
    The problem with the VOV is if your tube has a bend where it sits the VOV will not work.
    +1. When i was refurbing my system, I bought a variable orifice valve to try and it broke due to the bend in the pipe. I installed the regular version and it works great (at least for R12).

    Here's my thread which contains part numbers and process tips for A/C refurbishment..

    http://dmctalk.org/showthread.php?15...stem&styleid=1
    Last edited by DMC-81; 05-29-2021 at 06:24 PM.
    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.
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  5. #15
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    Quote Originally Posted by 81dmc View Post
    Actually I take it back. First Iím trying the 1.7mm Blue Orifice Tube p/n 38621 from a 2004 Ford F-150. If itís not enough, then Iíll try the Red 1.6mm.


    Got too much to do with the car. Getting ahead of myself lol.
    Please let us know how it works out. Never know if I will be forced to convert to 134.

  6. #16
    Administrator Ron's Avatar
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    Quote Originally Posted by 81dmc View Post
    I thought the same thing, but with an orifice tube being $3 and easy to replace, Iím up for an experiment.

    Iíve never had good ac performance in my car with all new components. I've tried everything but a different sized OT.
    The consensus has been, if you live in the extremest of climates, don't convert due to performance. And since I've never had a problem getting 134a conversions to do ok here (but not as well as R12), I haven't played with a VOV on a D-134a.
    Your results will be interesting!

    Quote Originally Posted by Helirich View Post
    The smaller diameter would make for higher "high side" pressures and lower "low side" pressures. But I would think it would make for shorter cycles because the low pressure switch would keep tripping. Not sure how it would effect on proformance.

    I will say that it's been my experince that converting r12 to 134a just never works as good. New cars are great, but the conversions suck. That's why I'm keeping mine R12.
    After thinking about this a bit, I believe we were both wrong. A cycle would be from cut off to cut off, i.e. OFF time + ON time). The cycle switch will obviously operate in the same range (~ON 50 - OFF 30 psi), so the low side would too. What we need to know is if there is a difference in the time it takes for R12 and 134a to drop from 50 to 30 psi, while the compressor is OFF. According to the WSM chart, at 100įF ambient, the clutch should cycle OFF when the Low side is ~30 psi and the high side will be ~200 psi. Now it gets complicated. The pressure-temp characteristics of R12 and 134a are very close within the low side's 30-50 psi range. (33įF -> ~30.1 psi for R12 & 134a) So I would assume the percent of charge in the high side would be very close also. But with the 100įF ambient, would the 134a also be 200 psi at cut off? (A Fluke chart shows 62įF -> 60.1 psi for R12 and 134a, with 134a pressures raising faster; R12 @ 200 psi -> 138įF. At 138įF, 134a will have 223 psi.) This would mean the high side would have higher pressures, in its operating range. The higher pressure would mean the flow through the orifice would increase, to a point anyway. But then again, 134a retrofit's call for a 10% reduction in the charge. ...too many variables and things I'm sure I haven't thought of to nail down for a system that nobody has figured out how to make work as well as stock...YET

  7. #17
    Senior Member 81dmc's Avatar
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    Quote Originally Posted by Ron View Post
    The consensus has been, if you live in the extremest of climates, don't convert due to performance. And since I've never had a problem getting 134a conversions to do ok here (but not as well as R12), I haven't played with a VOV on a D-134a.
    Your results will be interesting!
    I refuse to agree that R12 is the only option for the DeLorean. Others said the same of my W126 Mercedes, and I have converted that R12 system with no issues. Difference is, that system uses a block expansion valve. But even then, I had bad performance until I charged it using superheat and supercool methods for optimum performance. Results were chilling.

    IMO, all 134 conversions should be majority new parts with parallel flow condenser and PAG oil. If you donít do that, it isnít a good conversion.


    Anyways, once my car is driveable, thereís going to be a lot of experimenting and Iíll be sure to post the results in a new thread.
    VIN 831- Delorean.eu Roof Box, Double Din, Custom Instrument Cluster, QA1 Suspension.
    Other Classic: 1982 Mercedes 300SD TurboDiesel

  8. #18
    Administrator Ron's Avatar
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    Quote Originally Posted by 81dmc View Post
    I refuse to agree that R12 is the only option for the DeLorean.
    Who here said that

    Quote Originally Posted by 81dmc View Post
    Others said the same of my W126 Mercedes, and I have converted that R12 system with no issues. Difference is, that system uses a block expansion valve. But even then, I had bad performance until I charged it using superheat and supercool methods for optimum performance. Results were chilling.

    IMO, all 134 conversions should be majority new parts with parallel flow condenser and PAG oil. If you don’t do that, it isn’t a good conversion.


    Anyways, once my car is driveable, there’s going to be a lot of experimenting and I’ll be sure to post the results in a new thread.
    I agree. With an expansion valve you can constantly feed the evaporator with what it needs, rather than bounce across an "acceptable range".
    (But, you can do the same with R12 -- No matter how you tweak it, R12 will out perform 134a in the exact same system, due to 134a's higher discharge pressures.)

    ...and definitely use PAG/134a .

    That's a lot of part$ (especially with EEVs), may very well be worth it in FL/Vegas/etc. But, I personally don't see spending the time and money in this area, not while I'm sitting on a Snap-On R12 reclaim machine and 4 tanks of R12.

    Please post the process rather than just the results!!!

  9. #19
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    Quote Originally Posted by Ron View Post
    not while I'm sitting on a Snap-On R12 reclaim machine and 4 tanks of R12.
    !
    I used my robinair reclaim machine. I don't recall any perticular freon. It seemed to work. Did I screw it up for later?

  10. #20
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    Unless you have to remove the orifice tube, either because it is broken or plugged up, leave it alone. It is in a place where the pipe is bent and it can be difficult to remove without damaging that VERY thin aluminum pipe. Once you damage that pipe you are replacing the evaporator coil and it is NOT a fun job. I do not understand why some people feel they have to "convert". R-12 is readily available, it is not that expensive, and you don't need much.
    David Teitelbaum

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