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1966 Olds Toronado A/C

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    Originally posted by Mikel View Post
    Thank you both.

    A/C is working well enough, but when the car is moving at a high speed it is noticeably cooler, so I hope increasing condenser capacity will make that cooling performance independent of vehicle speed. Unfortunately the core support blocks the mounting of pusher fans in front of the condenser and I don't want to start cutting the car.

    Maybe a project for this winter.
    Get some coil cleaner for HVAC work. That car has decades of road grime on it. Also remove the evaporator. Clean it or replace both to be sure. Auto AC Kits had what I needed. Fast shipping and good pricing.


      Originally posted by muscle spasm View Post

      The metering device be it a POA or TXV, sets the low side pressure. That pressure equates to how cold the system will get.
      The Tx valve and the POA do different things. A POA valve system also has a Tx valve. The Tx valve meters refrigerant so it all boils by the exit of the evaporator It regulates the amount or volume of refrigerant in the evaporator, the POA regulates the minimum pressure in the evaporator.
      The Tx valve doesn't care (within a range) how cold or how low the evaporator pressure gets, only that the inlet of the evaporator and the outlet are the same temp/pressure. If you try and use it too far out of its design range, it can't control the refrigerant in the evaporator to make the best use of the surface area.
      Conversely, the POA doesn't care how much refrigerant is in the evaporator as long as the pressure never falls below its set point. It keeps the evaporator temp from going below freezing. It is more like a frost switch then a metering device. You need both a Tx and a POA in a POA system



        Sorry, I just saw the latest posts.

        This was posted on another board during a discussion on POA systems. I didn't realize the expansion valve in these systems was adjustable.

        Why is no one mentioning adjusting the expansion valve? There's a brass nut in the valve (looking from underneath) that has a hex hole for an Allen wrench. Turn that in while counting the turns, take that number and divide it in half and turn it out that amount. From the factory, they are usually 7 to 10 turns, so, it will end up 3.5 to 5 turns. I ran my 72 C-10 like this for 7 years without a problem with stock evaporator and condenser.

        Since a molecule of R134 is smaller then a molecule of R12 the restriction at the expansion valve must be increased to get the correct pressure differential across the expansion valve. This also helps to bring the low side pressure down. On systems without POA valves, only the expansion valve gets adjusted or replaced. On fixed orifice systems (78 and up), the orifice tube gets replaced by a variable orifice tube which is an expansion valve. R134 needs to be squeezed more.
        Which leads me to another question. When I overhauled the A/C system in this car, I replaced the expansion valve, I believe with the AC Delco recommended below by Rockauto (I can't find the order paperwork). Any chance this valve could not be set properly for my application?



          Tx valves sometimes can be adjusted to set the "superheat" which is how much above the temp at the inlet of the evaporator, the outlet is.
          All that trash about "molecule size" is just that , trash!
          The Tx's job is to look at the inlet temp/pressure and compare to the outlet. If the bulb and or the equalizing line is connected some distance from the end of the finned evaporator, some superheat is called for to be sure all refrigerant leaving the evaporator is in gas form.
          The Tx valve doesn't do this by molecule size but by pressure and temp. It doesn't care how warm or cold the evaporator is, only that the inlet (just after the Tx) and the outlet are close to the same temp, Be that 70 deg or -20 deg. Size of molecule and operating pressure don't matter. Pressure will be much higher at 70 than at -20 but the Tx will meter such that the outlet and inlet are about the same.
          The same Tx is used for R 12 and R134a, and the same superheat should also be used, in otherwards, no adjustment required.
          Sure, if you lower the superheat, you can lower the suction pressure, but that does nothing to increase the capacity of the system and runs a very real risk of "slugging" the compressor with liquid refrigerant.
          That post is by someone who doesn't understand what a Tx valve does.


            Thank you. Very interesting.


              This is for sale locally (R12). Any idea how much this tank weighs empty? Thanks.


                Propane cyl are sometimes marked with their empty weight, They may do the same for R12 look for a weight stamped into the cylinder near the top/valve.