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Help with completely new A/C system on a 35 year old car.

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    Help with completely new A/C system on a 35 year old car.

    I bought a car last year that came with no A/C components whatsoever, other than the hard lines back to the cowl, expansion valve, and an anti freeze switch. I flushed out the old lines first. I bought new compressor, condenser, receiver/drier, expansion valve, freeze switch, pressure switch, temp switch, o-rings all around, belt. All installed and checked for leaks. While trying to fit the compressor and hoses in all sorts of positions (the engine is fairly custom and the exact stock location isn't possible) I pretty much drained the compressor oil. So, I made sure to it was empty and added 4oz of PAG oil to it. I then pulled down a vacuum to about 25, as low as it would go and it held for 24 hours, so I proceeded to charge the system. I'm a noob, so I didn't fill it under vacuum to suck in the refrigerant, but rather filled the r134 as a liquid. After filling it a bit, the compressor does kick on and run, so I assume the setup is correct and working. I did a shit job of measuring what I put in, I think, and now I feel I may have overcharged the system, according to the gauge readings, but I'd like some input to confirm or rule out.

    According to documentation, my car should take 30oz. TBH, at this point, I am not remotely sure how much I put in. But, here are the readings:

    Static pressure is equalized around 100psi. From what I have read, that is high, should be <80.

    Running the car with A/C on @ 2.5k RPMs, the low side drops only to 50, but the high side runs up to 350. The previous owner wired the front pusher fan, which is now on the condenser, and the engine side puller fan to an adjustable fan temperature switch that kicks them both on at a certain radiator/coolant temperature. I believe I will have to figure out how to get that front fan in the A/C circuit so it comes on based on A/C pressure instead of coolant temp, but I need them both to help cool then engine coolant as the car overheats with them both working together. So, in non A/C weather, I think the car will run too hot. It's a supercharged stroker V8, so it runs very hot.

    Based on the above info, any insights, recommendations, etc?

    What did you do, steal this car? Your too afraid to tell us the make and model? Are you using the stock compressor? if so what make and model, if not what compressor are you using? Can't advise on the amount of oil you put in but some like the Delco A-6 take 10 oz of oil the compressor. Being 35 years old, it would have been R12 and when converting to R134a, the amount is somewhere between 75%-80% of the weight of R12 the system took. Minor changes like hose routing and even condenser type change doesn't change the amount of refrigerant.
    Pressures are high, but you already knew that. What the cause is could be several things, lack of heat rejection at the condenser, or it could be over charge (overcharge has the same effect as too small a condenser).
    I am hoping you didn't let air in after evacuation then added the refrigerant, if so, draw it down and start again, once the system is pulled down, you feed the refrigerant in under vacuum, it will soon show pressure. If you have air in the system the pressures will be high.
    Your gauges may be off a bit, the higher than ideal reading under vacuum, higher static pressure reading all point to gauges calibration being off a bit.


    • vball23
      vball23 commented
      Editing a comment
      I didn't mention the make/model because it is so far from stock, it didn't seem relevant. 1985 Porsche 928 stroker v8 with a Vortech supercharger. Sanden compressor, not stock. SD508 I believe. All the A/C parts are aftermarket except the expansion valve and the various switches.

      What I have figured out so far is that the fan on the condenser isn't being triggered by the A/C circuit, since it's wired to an aftermarket adjustable temp fan controller. I am going to run a wire from the appropriate pin on a 14-pin underhood connecter to a relay and then to this fan. That should trigger it to come on when the compressor is on. I'll check the readings with the condenser fan running properly.

      If that doesn't fix things, I'll draw it down and start again, feeding it under vacuum.

    Friend: You posted a comment not a reply at this site look down for "write something" at least my view shows that.

    OK: You have a total unknown creation of a machine with parts that you may have in place that have some chance. A/C part is as much a specialty to a motor vehicle as the whole rest of one so I suggest you just vacuum it down, unplug or disable compressor from being able to work and mark on it you added 4 oz of which type of PAG oil!

    Now the job should be find a shop that has total equipment and knowledge to create a new spec for this for how much oil and how much weight of the charge from an absolute vacuum it holds and works if at all without more alterations so there's something to deal with looking forward.

    You said "noob" to this says it all. It's not easy and this is going to take unreal understanding of exactly what a tech finds right in front of them if any issues with layout of items is all wrong stop there or proceed at all.

    I can't know if you don't and seems nothing is known just know anything to make air conditioning with a compressed gas will not work well or last if all mixed with air take a full vacuum for where you are by altitude is a factor.

    The real problem is doing it wrong, allowing air or moisture all thru this now you'll ruin any chance of the working to cool this thing apparently have tried hard is going to take in person highly skilled person with unreal equipment to make the call now.

    Find the right person/shop is now the job the equipment alone would way out cost any possible savings now to you. If not up to some unknown cost of that leave it disabled seems this creation wasn't meant for A/C by whatever it was supposed to be if whole car worked out as just the car alone for whatever you wanted to do with it,
    MetroWest, Boston


      I think the best way is to take it to the professionals,like Tom suggested. You need to have some refrigeration and automotive AC knowledge to be able to be guided from here to get the AC working right.There are a lots of factors to take in considerations when you are custom design and fit an AC to a car. The SD508 is an R12 compressor and I don't think will like the PAG oil very much (I would have used Ester oil),most likely the front mechanical shaft seal won't last you very long ( for the age of that compressor more than likely the front shaft seal is leaking) Sorry to say but without having any condenser cooling I would have not attempted to regas that AC ( again knowledge plays a good factor) especially trying to regas it guided by pressures. Please don't take it the wrong way, ( I am new here like you ) I am sure the ppl on this forum are willing to help as much as they can but it will be too hard to guide somebody without any AC knowledge,to help you make a custom AC work,this is my opinion only,maybe other members here are willing to put in the hard work and guide you till the end.Good luck with your project.


        I moved to its own thread.
        Last edited by Cornbinder89; 06-02-2020, 02:48 PM. Reason: started a thread of its own.