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  1. #1

    Question Trying to add R-12 but it's not willing to draw from the can - is this normal?

    Hello all - I had a few cans of R-12 laying around, so I decided to try to add AC back to my car which hasn't had it in about 25 years. I kept the original evaporator, but replaced all the lines and the condenser in front. I rebuilt the factory Nippondenso compressor and vacuumed down the system. It held for a week so I moved forward.

    Here in Michigan last night it was about 67-72 degrees, so I attached my gauges, along with a Robinair side-tap (since the tops of the cans are not pretty) and tried to add a full can to the car without the engine running. It took about 1/2 the can and that was it, so I started it up and it eventually took the rest. Then I added a second can and it probably took an hour or so take the second can - with me twisting and turning the can. I'm worried about trying to add the third can. Right now the air is blowing very cold with the 22-24 ounces it has.

    Is this normal? Am I missing something?

    Thanks,
    Howard

  2. #2
    FEP Senior Member
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    I had a couple of cheap can taps where the check ball in the tap would actually completely block off flow out of the can. Very frustrating. I had a hard time with the first 3-4 cars using those stupid taps until I figured out what was going on. Really any restriction between the can and the inlet quick disconnect could cause the issue. What is the capacity of the system (refrigerant) when full?
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  3. #3

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    Are you sure you are connected to the low pressure side?

  4. #4

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    Hi guys, The refrigerant capacity is 2 and 1/2 pounds, or 40 ounces - according to my hayes manual.

    Pretty sure I'm connected to the low side - it's the fitting on top of the compressor that the accumulator hose is attached to.

    Thanks,

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    Could the new orifice tube be designed for R134A and causing an issue?

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    If it is blowing nice and cold now , dont worry .
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    FEP Senior Member Tigger's Avatar
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    I just charged my Saleen with R12 a couple weeks ago and it took a while to charge as well. It took probably 45 min easy to charge it.
    Last edited by Tigger; 06-08-2019 at 12:27 AM.
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    FEP Senior Member gt4494's Avatar
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    I have extra long hoses and would always set the can down on the intake with the car running. Heating the can will help force feed the system.
    "If you can't explain it simply, you don't understand it well enough."
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  9. #9

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    Quote Originally Posted by gt4494 View Post
    I have extra long hoses and would always set the can down on the intake with the car running. Heating the can will help force feed the system.
    Good to know. Seems like it takes forever to charge a system from zero -- even with 134a and the cycle switch jumped to keep the compressor running constantly. Thanks for the tip.

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    Double post... dad-gum it

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    I can usually get a 12 ounce can to empty in 3-5 minutes depending on how things are going. What does your low pressure gauge show when you are filling? Remember the can pressure has to be higher than the low side pressure otherwise it isn't going anywhere. Sometimes shaking or warming the can as mentioned can help. You can always tell when the refrigerant is going in because the can gets/stays cold.
    Last edited by KevinVarnes; 06-10-2019 at 12:18 PM.
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    FEP Senior Member gt4494's Avatar
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    Quote Originally Posted by KevinVarnes View Post
    I can usually get a 12 ounce can to empty in 3-5 minutes depending on how things are going. What does your low pressure gauge show when you are filling? Remember the can pressure has to be lower than the low side pressure otherwise it isn't going anywhere. Sometimes shaking or warming the can as mentioned can help. You can always tell when the refrigerant is going in because the can gets/stays cold.
    Doesn't the can pressure need to be higher? otherwise the system will try to pressurize the can.
    "If you can't explain it simply, you don't understand it well enough."
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    Sorry. Brain fart. Yes you are correct. I've got my mind on several different things right now. Thanks for the heads up. I fixed it.
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    FEP Power Member Saturn V's Avatar
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    Good tips from KevinVarnes above. Like he said, there may be a restriction in your hoses or can tap. I, too, seem to recall it only taking a few minutes per can to fill. You can gently swirl the can to help keep the refrigerant closer to ambient temp to speed the process a little. Remember, the heat to vaporize the refrigerant in the can has to come from the metal of the can. You’ll want to put in the correct amount of refrigerant. Just because the air seems to blow cold now, doesn’t mean your system will perform well in hotter weather. Also, pressure too low will cause the compressor to cycle on/off too frequently. I seem to recall that my 84 required 42 ounces, per the sticker under the hood. A 12 ounce can will really only deliver about 10.5 ounces of refrigerant, after subtracting the tare weight of the can. So my system took exactly four 12 ounce cans (4 x 10.5 = 42).


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  15. #15

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    Quote Originally Posted by Saturn V View Post
    ... A 12 ounce can will really only deliver about 10.5 ounces of refrigerant, after subtracting the tare weight of the can. So my system took exactly four 12 ounce cans (4 x 10.5 = 42).
    When working with small cans, I always weigh them full with the tap attached, and mark the weight on the top
    of the can with a Sharpie. Once empty, I weigh them again, same as before, and mark that weight, then mark
    the difference. I seldom see more than 0.1 ounce deviation plus/minus in the difference from can to can.

    A 12 ounce can of refrigerant generally contains... 12 ounces of refrigerant, exclusive of the tare weight.

    Reading the first post in this thread, I am curious exactly what was used to vacuum down the system. I'm also
    curious how much, if any, refrigeration oil was added to the compressor and condenser before reinstalling them.

    A 'Venturi' vacuum pump is not going to vacuum down deep enough to boil moisture out of the system, unless
    it's a very hot day, and you've got a very strong source of airflow. Also, I have seen leaks that only appear
    once the system is pressurized, so if you have access to dry nitrogen, that is a much better testing method
    than letting the system sit under vacuum. A small amount of refrigerant can be fed in before the nitrogen, if
    you have a sniffer, so that if it leaks, you can find out where. Most common leak points on the Fox Mustangs
    are the SpringLock couplers.

    When charging a system from scratch, I pull a deep vacuum (with a proper vacuum pump), then charge into
    vacuum on the high side, with the can inverted, to charge liquid instead of gas. This does not damage anything,
    or pose a safety hazard, because the compressor is not running. Once the flow stops, I then the high-side valve
    on my manifold set, and open the low-side valve. At that point the system has enough pressure to engage the
    compressor clutch. I finish off with the can upright to avoid putting liquid into the low side. To keep the can
    pressure up, I place the can in the path of radiator airflow.

    An empty system should always be charged by weight, to the specified capacity. On larger capacity systems
    like a Fox Mustang, I usually get ~1.5 cans in without the aid of the compressor.
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    FEP Power Member Saturn V's Avatar
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    Romper Room is over, Mr. Cook is back! Yes, I think you're right. I went and weighed one of my spare full 12 oz. cans a few times this morning and got inconsistent readings from my scale that varied by up to an ounce. Also, the can is marked "12 oz. net weight". Amateurs like me need to be careful about taking one (incorrect) experience and extrapolating it.
    Last edited by Saturn V; 07-04-2019 at 12:20 PM.
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    Moderator wraithracing's Avatar
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    The other issue I have run into with my hoses and fittings is that often if I tighten the fittings onto the can valve or even the shrader valve too tightly the seal/gasket inside can be compressed or distorted and cause an obstruction to the flow of freon. Often just a 1/4 turn or less of the fitting to loosen it will solve the problem. In my experience, I have found that looking for the simple, easy solution first is often to my benefit. Good Luck!
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  18. #18
    FEP Senior Member gt4494's Avatar
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    And remember that too much Freon will freeze the system and the ac air will not be cool and at a reduced airflow.
    "If you can't explain it simply, you don't understand it well enough."
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  19. #19
    FEP Power Member 85stanggt's Avatar
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    Quote Originally Posted by wraithracing View Post
    The other issue I have run into with my hoses and fittings is that often if I tighten the fittings onto the can valve or even the shrader valve too tightly the seal/gasket inside can be compressed or distorted and cause an obstruction to the flow of freon. Often just a 1/4 turn or less of the fitting to loosen it will solve the problem. In my experience, I have found that looking for the simple, easy solution first is often to my benefit. Good Luck!
    This is exactly what I was going to write. If you turn the tap all the way in, it will obstruct flow. Back out about 1 turn and it'll flow like no tomorrow. Shouldn't take that long to empty the can. Never turn the can upside down or you will suck in liquid refrigerant, which could be catastrophic to the compressor.

    Make sure you have mineral oil in an R12 system to lubricate the compressor. Usually you replace the amount you took out of the compressor when you remove it.
    1985 Mustang GT Convertible
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  20. #20

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    Hi guys, I'm back from vacation and back on the mustang. I made a bit more progress on it and found a mistake I was making. First off, I used a Robin-air vacuum pump to pull it down as low as it could - about 29" or so. I started the car, turned on the AC, noticed it was getting cold with only the two cans in it, I was trying to diagnose what was going on and all of the sudden, my pressure relief valve pulsed a few times and scared the crap outta me. I immediately shut it off.

    Where I think my mistake was this; Since I made my own turbo conversion about 25 years ago, I use an electric fan which only turns on when the car gets hot. I was making too much pressure because during my fill process, the fan was not running because the car was not warm enough. So, I tapped into the power wire of the clutch wire and now have a relay turn the electric fan on when the compressor gets power - unfortunately, the wire is only getting around 10-11 volts so the relay doesn't always come on. So far, so good for not opening the pressure relief valve, but the belt is squeaking terribly - also due to customization's that I had to do for the turbo conversion. I think the belt is not getting wrapped around the compressor well enough.

    Thanks!

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