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Abandon rear AC evaporator

CmathCmath TexasPosts: 3
edited September 2018 in Chevrolet
There is a leak in the rear supply hose to the rear evaporator on my 2007 Tahoe. I want to cap the supply and delivery lines near the compressor. will I still have a working front AC system? The line is $350 and has to be installed by a chevy dealer due to some required dealer tool. Cost estimate $1,300.

Comments

  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,450
    edited September 2018
    You might write to THIS VENDOR on eBAY and ask them if they send complete instructions with their block-off kits.

    I think even if you successfully block off the rear, you're going to need expert AC people to properly recharge the system. You might even search in your area for an AC specialist who has done this type of block-off before.

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  • CmathCmath TexasPosts: 3
    Thanks. I asked them if they have a kit for the 2007 tahoe. It has the bolt on block style fittings for high and low-pressure lines. When done need A/C guy because the freon level will be lower right?
  • imidazol97imidazol97 Crossroads of America I70 & I75 Posts: 23,162
    I'm surprised the company supplying the kit doesn't have data for what would be the correct weight of the charge for the freon after removing the volume of the rear tubes and evaporator.

    A good AC shop should know what's recommended. They might be able to do it by the pressures, but the variable displacement compressors are tricky for amateurs like me.

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  • thecardoc3thecardoc3 Posts: 4,953
    The rule is you charge the system as if it never had the rear AC, and then you have to test and adjust as required. The testing requires that you understand how to use the enthalpy chart for the refrigerant when a variable displacement compressor is involved.


  • CmathCmath TexasPosts: 3
    I bought the kit. will install next week and have a shop recharge it. Thanks for \all your help.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,450
    edited September 2018
    ENTHALPY: a thermodynamic quantity equivalent to the total heat content of a system. It is equal to the internal energy of the system plus the product of pressure and volume.

    (Had to look that one up!) :p

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  • thecardoc3thecardoc3 Posts: 4,953
    edited September 2018
    LOL, you aren't alone. I had to go through numerous definitions and examples to get competent at really teaching the concept. To arrive at the full correct charge we have to maximize the heat that the system can move, which BTW doesn't happen at the maximum charge. Heat is more than just the temperature. For example:

    Which has more heat in it, the warm refrigerant liquid entering the evaporator or the ice cold gas leaving it? The cold gas of course has much more heat in it. That's where explaining the latent (missing) heat of evaporation comes into play. You can see the heat that was picked up during vaporization when the gas is compressed by the temperature rise at the compressor. Then the enthalpy chart helps show how efficient the system is by how much the refrigerant can be cooled as it condenses back to a liquid. The shape of the numbered polygon in the center of the chart is defined by the efficiency of the heat transfer in both the evaporator and the condenser.
  • kyfdxkyfdx Posts: 116,324
    I'm still not exactly sure how A/C or a heat pump works. I sort of get it, but not really. Guess I was better at math than physics.

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  • thecardoc3thecardoc3 Posts: 4,953
    When the gas is compressed the heat in it is concentrated so the temperature of the gas rises. Heat always moves to something colder, so the first goal is to get the temperature of the refrigerant to rise above the ambient temperature. In automotive systems you will usually see compressor outlet/condenser inlet temperatures around 130-160f. With the refrigerant temperature that high, the heat in the refrigerant can be transferred to the atmosphere. As the refrigerant loses heat it falls below it's boiling point (which is raised by it being under pressure) and condenses into a liquid. As it does this it releases a large amount of heat, known as the latent heat.

    The refrigerant then goes through the expansion device where we get a resulting drop in pressure. The pressure change changes the boiling point of the refrigerant and it absorbs a large quantity of heat as it evaporates. The heat that it absorbs comes from the air inside the passengers compartment.

    Watch this video which explains enthalpy quite nicely.


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