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AC conversion questions

Discussion in 'The Garage' started by bp71k5, May 3, 2007.

  1. bp71k5

    bp71k5 3/4 ton status Premium Member

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    Hi,

    I'm adding a factory AC system to my 71k5 which did not come with AC. I've got most of the interior parts hooked up and working like the heater core, fan, and control cables.

    I ran into some forums talking about using a FOT (Fixed orifice Tube) instead of the TXV (Thermal Expansion Valve). Some say both will work, but there's lots of talk about using the FOT instead.

    I also heard a parallel flow condensor is a good upgrade when using an expansion valve.

    Any AC guru's out there? Is there a big advantage to using an FOT?
     
  2. AZ79K5Project

    AZ79K5Project 1/2 ton status

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  3. throttleissues

    throttleissues 1/2 ton status GMOTM Winner

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    The FOT system is just simpler. The TXV system often uses a POA valve also. this keeps liquid freon out of the compressor. The FOT system uses the accumulator to do that and just cycles the compressor (using a low pressure switch) to keep the pressures in the right range. If you use the FOT system and R-134a it is usually necessary to turn the low press sw down a little to get efficiency back. A lot of the conversion kits have a note about that in the instructions. The factory changed systems to FOT to save money. The odds of the valving in the TXV system being good if you salvage them from another vehicle is highly questionable. Finding reaplacements is probably going to be an adventure, so the FOT system would most likely be the easier and more trustworthy swap. If you are pulling the parts from another truck, buy a new FOT and install it in the line before you charge the system. They do get plugged with debris from time to time, but they are cheap and easy to find. Good luck on the project.
     

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