4250 a.c. pressures.
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    4250 a.c. pressures.

    I replaced compressor, drier and expansion valve in my new tractor due to the compressor leaking ibn the center of the body. Didn't fail so there wasn't any debris in it. I have the recommended 8 oz of oil in it. But my low side gauge won't come down below 45. It's been staying up around 70-80. So I recovered the Freon and added 2lbs 12oz of Freon and it finally came down to the 45. Everything I've read says these tractors take 52-55 oz of Freon which is 3lbs 4 oz. I tried that and it stays up around the 70. One guy said charge it till the sight glass is clear and no bubbles. I'm just looking for more advice or pointers! Thanks

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    Superglidesport's Avatar
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    You should have the engine running at high RPM (~1800) when you check the AC gauge pressures. When checking at idle it's not uncommon to have high low-side and low hi-side pressures.

    If you're undercharged you'll see the low side drop too low or into a vacuum at higher speeds.

    Generally 20-50 PSI Low and 170-250 PSI High pressures (minimum 150 PSI differential) indicate that you're working A-OK and duct temperature should be adequate.

    High ambient temperatures with high humidity will limit what you're expecting for duct temperature. If testing under adverse temperature & humidity conditions a 10*- 15* duct temperature reduction is as good as it gets.
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    I assume you are charging with R134A? What is your high side pressure readings? Are you sure that the condenser and radiator are clean and getting good air flow through them? Is the viscous fan drive operating normally? This system does need 52 ounces of refrigerant to operate normally and at that charge level, the low side shouldn't be any higher than around 30 psi.
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    Yes 134a. I have blown the radiator and condenser out so I feel like it is flowing appropriate. High side is between 250 and 300 today. It was 95 here in Arkansas. Low side came down to 35-40 with 2 pounds 10 oz. At 1600-1800 rpm finally.

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    It's my understanding that adding R134A until there are no bubbles in sight glass will over charge system. 36 oz of R134A is what I install in my 4255. I rarely look a low pressure gauge just monitor high pressure when adding refrigerant.
    Last edited by Tx Jim; 05-15-2018 at 06:56 AM.

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    Was a good/long vacuum pulled on the system prior to rechaging? Moisture in the system will boil at high pressure/high temps and not allow the system to cool down properly.

    Check to make certain the heater valve is fully closed. As a note, I've had to replace a few heater valves because of engine coolant leaking past, allowing warm/hot water through the heater core.

    Another thing.....When charging the a/c system, I allow a very few bubbles to show in the sight-glass.
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    Quote Originally Posted by Tx Jim View Post
    It's my understanding that adding R134A until there are no bubbles in sight glass will over charge system. 36 oz of R134A is what I install in my 4255. I rarely look a low pressure gauge just monitor high pressure when adding refrigerant.
    Unless Deere does something different than every other A/C system out there, bubbles indicate a low charge.
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    Quote Originally Posted by mamu View Post
    Yes 134a. I have blown the radiator and condenser out so I feel like it is flowing appropriate. High side is between 250 and 300 today. It was 95 here in Arkansas. Low side came down to 35-40 with 2 pounds 10 oz. At 1600-1800 rpm finally.

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    Be careful, a low charge will cause ice to form on the evaporator, and that will restrict air flow.
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    Yes my machine recoveres then does what it calls a deep vacuum. Which pulls the low side down to 30 inches below 0 for about 15 min. Then I go ahead and pull another 10-15 min too.

    You can see where it's confusing to me. One person says 36oz works for them. Some say 52oz. The spec from AP air is like 2.75-3.25 pounds.

    Bubbles? No bubbles? I've had 3.5 pounds in this machine and still had bubbles and low side was about 65-70.

    I can make a big truck and a pick up work and blow cold. I'm sure this isn't a whole lot different but I'm just not familiar with it. So I'm reaching out to y'all for help.

    Thanks

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    My thread kinda died. Hope I didn't come off sounding like a jerk. I'm here asking for help.

    Thanks everyone.

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