POA Valve removal, expansion valve

Discussion in 'The Big Chill' started by black70buick, Oct 30, 2018.

  1. black70buick

    black70buick Well-Known Member

    Can I bridge the POA ports for the expansion valve and straight up remove the POA?

    I am looking at the delete kit and scratching my head. https://originalair.com/73-early-74-buick-apollo-ac-poa-delete-kit-15-51

    I have a high pressure switch on the R4 compressor model that I have, so to me the question is what does the POA valve delete for $99 really do? ...nothing except in theory provide a port. BUT I am smart enough to ask the good guys here on whether this is true.

    OR can I just modify my POA to not regulate pressures and temp thus leaving it in place and wiring the pressure switch?
  2. philbquick

    philbquick Founders Club Member

    That system adds a low pressure cut off switch to the low side which cycles the compressor like newer systems do. An R4 is designed to cycle so it should be OK. To make a cycling system work you will need to either replace or re-calibrate your expansion valve. you can also eliminate the expansion valve and replace it with a variable orifice tube that will drop into the inlet tube of the evaporator.

    Last edited: Oct 30, 2018
  3. black70buick

    black70buick Well-Known Member

    I have managed to research a little more since the posting, but I still have questions. To recap my understanding, The only thing that needs to be adjusted according to Original Air (https://originalair.com/converting-to-134a-general-motors) is the POA valve if I am retaining it - it is the low side by pass (I was wrong in my original post) and the by pass pressure needs to be reduced from 30PSI used for R12 down to 20PSI for 134A. However, a delete tube makes sense and still has provisions for connecting the expansion valve.

    So, if I under stand you correctly. I can do the following:

    Option 1:
    Buy or service the POA for 134A
    Retain the expansion valve (or replace if faulty)
    Wire up the compressor clutch only (ignore the high pressure because the expansion valve does the job)

    Option 2:
    Buy the POA by pass
    Retain the expansion valve (or replace if faulty)
    Wire the compressor clutch and the low pressure switch (ignore the high pressure because the expansion valve does the job)

    Option 3:
    Buy the POA by pass
    Buy the Orfice Tube VOV (dimple the tube to secure the orifice thus eliminating the expansion valve)
    Wire the compressor, low pressure switch and high pressure switch to cycle clutch accordingly.

    I like option 3 because to me it seems the simplest and most cost effective.

    Questions with option 3:
    Am I to only use 80% of R12's spec when using 134A in this set up?
    Do you believe the condenser and Evap core sizing can be retained - I do not have to change either correct? I will flush them, because they are older and flushing is still effective.

    No matter the option, I will flush the components and purchase a new receiver dryer. I already have the rubber lines/hoses replaced for 134A. Naturally all ORings with be addressed as well as correct oil.

    Please chime in where I may have a misunderstanding. Is option 3 accurate in my understanding?
  4. philbquick

    philbquick Founders Club Member

    Option 3 is what I would do. I did some of my own research 20+ years ago using a 72 Caprice as a test case and found that if I counted the turns on the expansion valve calibration and multiplied by .6 it sort of worked with R134. In other words, if the adjustment was 8 turns I re-calibrated it to 4.8 turns and it worked OK but not great. The variable orifice tube is already calibrated for R134 so why bother. You will need to remove the spring and needle valve from the old expansion valve. I can tell you did your homework since you caught the dimpling the evaporator tube detail (that I forgot to mention). You need to have as much air going through the condenser as possible, a 7 blade fan with a thermal clutch or high volume electric fan is a must. On my 72 C10 I filled the gaps between the fan shroud and the core support and the core support and condenser with pipe insulation from Home Depot to make air flow more positive. You should flush everything when converting from R12 to R134, they make solvent specifically for this purpose and yes, always replace the filter/dryer. I noticed in the mid 70s or so they added a thermostat to the evaporator box to prevent ice-up, yours may have that. If you don't have that you may want to add if you have an ice-up problem on long trips.

    That's everything I know about it. Keep us posted on how it works out.
  5. flybyspam

    flybyspam Active Member

    Philbquick, For option #3 when you gutted the expansion valve; was it necessary to retain the equalizer line from the expansion valve to the POA valve? I purchased a VOV and have read through the Buick Service manual for expansion valve operation. I haven't been able to determine if the equalizer line is still necessary?
  6. philbquick

    philbquick Founders Club Member

    I know there's a port on the POA bypass for the low pressure switch, I'm not sure there's one for the equalizer tube (if there were it would be just for show), it would be good to cap it off if there's no place to connect it. It would be better to use a Ford pressure switch since they are adjustable and the GMs aren't.

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