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F22Chris’s AC Thread

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    F22Chris’s AC Thread

    Automotive air conditioning systems can be confusing, so I wanted to make a thread the community can refer to. With the summer months approaching, I’m sure we all want our air conditioning systems working.

    There are two main types of systems in cars. TXV and piston. The most common are TXV (thermostatic expansion valve) systems, so that’s what I’ll cover here.

    What are the components that make up the AC system?
    The main components are:
    1. Compressor: This is the big, engine mounted serpentine accessory that moves refrigerant through the system.
    How does it work?
    When you push the AC button, it engages an electromagnetic clutch that turns a wobble shaft attached to two pistons.

    The compressor takes cool low pressure VAPOR refrigerant and compresses it. The compression increases the pressure and temperature of the VAPOR refrigerant, and is then sent to the condenser.

    2. Condenser: This is the thin looking radiator mounted in front of the engine radiator. The principle is the same as it is a heat exchanger.
    How does it work?
    When the refrigerant enters the condenser, it’s a hot VAPOR, and as it runs through the condenser, it’s then cooled and CONDENSED into a LIQUID. Easy right?

    3. Accumulator/Drier: This is like a catch can for your AC system. It stores unneeded oil & refrigerant, and traps any moisture or contaminates in the system.
    How does it work?
    The high pressure LIQUID enters the accumulator, and is filtered. It also contains a material called desiccant. Desiccant is what removes any moisture that may have been introduced into the system. You know when you open a new package, and there’s a tiny pack of silicone that says “don’t eat”? That is a type of desiccant.



    4. Sensing bulb: This is a temperature sensing bulb filled with refrigerant attached to the outlet of the evaporator.
    How does it work?
    As the evaporator outlet temperature increases, so does the pressure within the bulb. This increase in pressure presses down on the diaphragm, opening the expansion valve. As it cools, the pressure drops, and the valve closes

    Expansion valve: This separates high & low pressure sides, and removes the pressure of the refrigerant which allows for expansion. Its role is to control the flow of refrigerant into the evaporator.
    How does it work?
    High pressure LIQUID enters the valve, and is metered by a diaphragm connected to the sensing bulb.



    5. Evaporator: This is the small radiator-like component located behind the dash. It works opposite of the condenser, as it converts a liquid into a gas.
    How does it work?
    The now lower pressure LIQUID is turned into GAS inside of the evaporator. The pressure reduction causes the refrigerant to become very cold. The refrigerant then absorbs heat from within the cabin and vaporizes. The heated refrigerant then travels back to the compressor to start the whole process over again.



    So in a nutshell, AC works by removing hot air from inside the car, and displacing it outside.

    As most of us know, from the factory, CB7’s used R12 as refrigerant. It’s since been discontinued as it was related to holes in the ozone layer.
    All newer vehicles use R134. The main differences in the two are the molecule size and oil compatibility. R12 molecules are larger, which actually makes it more efficient than R134. R12 oils don’t mix with R134. You will ruin your AC if you just throw conversion ports and a can of AutoZone special in the system.

    I want to convert my R12 to R134, what do I need?

    Tools:
    -Basic hand tools
    -can cap
    -Scale that can measure ounces
    -Thermometer
    -Manifold gauge set with extra yellow line
    -Vacuum pump

    Parts:
    -R134 compatible AC o-rings
    -R12 to R134 conversion service ports
    -R134 refrigerant
    -Ester oil
    -UV dye
    -New expansion valve & bulb
    -New accumulator/drier

    The parts listed are a minimum one will need. Some may have locked up compressors or failed clutches. Some may have gotten into a fender bender and cracked their condenser. Obviously failed parts will need to be replaced.

    Now what?

    -Legally evacuate the system.

    -Replace all failed components, install new service ports, expansion valve/bulb, and accumulator/drier while replacing all o-rings as you go.

    -Once the system is together and sealed, attach your gauges. Blue to low pressure side, red to high pressure side, and yellow to the vacuum pump. Tighten the blue fitting. Let the pump run and enjoy a beer or six. When you come back (30min+) the gauges should read 28-30inHG. If not, double check all connections are tight, and you didn’t pinch an o-ring.

    -With vacuum still held, and your gauges attached, close the low side port. Measure out the amount of ester oil needed plus an ounce of UV dye & mix it up. This is to help you from potentially sucking in air. Fill the yellow line with oil to further eliminate air introduction. You’re going to use the vacuum in the system to suck up the oil into the system. So you don’t suck up air, when 1oz of oil is left in your container - stop & close the low side port.

    Gauge sets have fittings on the end of the lines. Even the middle one. To actually suck up the oil, you’ll need to cut off the fitting. This is why you might need an extra line. One with the fitting, one without.

    -You can now charge the system with refrigerant. When converting to R134, you need to use 0.7 of the amount of R12.(See list for conversion). Put your can cap on your can of refrigerant, attach it to the yellow line fitting, and put it on the scale. Open the low side, and measure out the amount needed. So if you have a 50oz bottle of refrigerant, and it calls for 25oz. Close the low port at 25oz. Of course the math won’t be that basic as you’re also weighing the can, cap, and some of the line.

    -Once your all charged up, stick your thermometer in a vent and turn the AC & blower on to max settings. Hold around 1500rpm for 5 minutes to let the system regulate. If it puts out 45* or cooler air, you win! If not, you may need to add more refrigerant. Check chart for proper gauge readings. If your readings are good, live with it. Don’t just keep adding more refrigerant.

    Oil and Conversion list:
    1990-1992
    Oil: 4oz
    R12: 32oz
    R134: 22.5oz

    1993
    Oil: 4.5oz
    R12: 30oz
    R134: 21oz

    Gauge readings at given temperatures.
    65*F
    LOW: 25-35psi
    HIGH: 135-155psi

    70*F
    LOW: 35-40psi
    HIGH: 145-160psi

    75*F
    LOW: 35-40psi
    HIGH: 150-170psi

    80*F
    LOW: 40-50psi
    HIGH: 175-210psi

    85*F
    LOW: 45-55psi
    HIGH: 225-250psi

    90*F
    LOW: 45-55psi
    HIGH: 250-270psi

    95*F
    LOW: 50-55psi
    HIGH: 275-300psi

    100*F
    LOW: 50-55psi
    HIGH: 315-325psi

    If it gets hotter than that where you live I’m sorry. If it’s hotter, low side readings should stay 50-55psi, and high side readings can reach up to 350psi.

    Gauge readings can also help diagnose problems within the system.

    LOW side | HIGH side

    Low Low - Low charge. Leaks in system.
    Low High - Blockage. Replace expansion valve & drier.
    High Low - Usually failing compressor
    High High - Over charged

    I hope this will cover most of the future questions on AC. If I missed anything or got something wrong please let me know so we can have the most accurate information possible.

    #2
    Spot for updates.

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