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Hot Rod Air Conditioning recharge pressures... need expected values

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  • #16
    Ran it in the middle of the day. About 80 in the shade and about 90 out in the sun. Ran 36°F to 44°F and it was toasty in the sun. Note that this is a convertible with the top down and a/c blowing out into the open. Temp taken at the center outlet.
    Another thing I did while system was empty was to relocate the a/c hose away from the exhaust manifold....so it's no longer within a few inches of it...now about a foot away.
    And, YES, it does drip condensate as expected.
    I will try a different temperature gauge, but I suspect that's fairly accurate from using on my other vehicles.
    I added a picture of the relative condenser sizes just for info.
    Last edited by silvernblack; 10-15-2018, 11:35 AM.


    • #17
      Dislike page 2 or more but here goes. It's working well, better than any Vette with that basic body I could ever make just poor air flow, angled radiator and condenser on if not the same an OE one had the low side metal line so close to glowing hot exhaust figured best that was going to happen.

      Anyhow all my checks - so far mind you is air temps from real evap temps gain at least 4-5* F between it and the center vent even so you are really close but seeing it drip can work then freeze some back and forth right there.

      Which system is this now CCOT or TXV set up? Matters as either can have temp or pressure slow downs or cycling set to prevent it from getting too cold just for this reason and some will do that on purpose if no other side effects let it be but it's NOT intended to really get that low and stay there.

      The same therno is sold and works from Harbor Freight or other places is digital read out and fast enough. Faster I a wired thermos like you might use at home toss the wire out a window and read both in and out temps can be used to hang sensor for "out" in front of grille and other end on dash you can see both and what changes at what RPM and even test it with water over evap (beats any air for cooling evaps) see the maxes out efficiency and what is quits at and must quit.

      If you can't make this quit you risk choking the compressor when cooler if it's all hooked up right just defog or defrost window when way too cold it could compress but shut down flow or disengage clutch just so you didn't hydro-lock up a compressor as a default or can wouldn't work and you could be walking over it never mind A/C at all. That's the point to prevent that.

      Enough. I'm near sure your thermos isn't on the mark and not just me but check them with each other have dozens of assorted ones,

      Last note on why A/C can come on off season is the mostly lie that it dries the air so when heated it works much faster is foolishness IMO as air can't be wet if super cold out. Other is to let some oil flow thru off season is important. I can hear either of my own if just parked with a warm engine (both V8s) the heat of it cooling down heats refrigerant so it's static pressure says it can operate just for a few seconds sometimes even when down in the teens.

      Yes, you didn't ask but the two vehicles I use I have thermos in front for incoming air and down a center vent all year long so I can see just what it's up to anytime under what conditions driving along both now older vehicles same game though but watching so far I've avoided any repairs to my own if not where expected quick disable compressors so they don't run when low (would be why) and burn up for lack of lube. So far so good for decades of doing that on my own keepers of way too many vehicles (classics to antique ones) over the years,

      MetroWest, Boston


      • #18
        My experience in going with a bigger condenser is it doesn't change the charge amount hardly if at all. Many time the tubes are smaller on the newer condensers so the surface area is greater but the volume doesn't change much. I'd go back with the spec and try it.


        • #19
          If you went larger for a real '68 Vette condenser the new one will be for 134a and may not use as much as the smaller one. Tough to know specs now if not plain said so I've done some OE R-12 swaps stayed R-12 said reduce the known charge by an exact known amount with the new part no other alterations best guess is you are just taking stabs at how much. If a Vetter already said I'm near sure that is at a high angle not just up and down and channeled thru as best as could be done for air brand new these cars overheated on hot days never mind if A/C or not was the first year of that body.

          Still I can't see how charge amount is producing the low temps seen. You could verify my thoughts on that by just running vent only, no A/C and watch air temp coming in thru now cowl up by wipers see it get warmer than that at the vents there plain is engine heat involved at least some gets thru firewall to dash,
          MetroWest, Boston


          • #20
            I went and got another 2 thermometers per suggestions since the temps I was reporting did not make sense. Does 40° to 44°F sound more reasonable and in-line? Ambient temperature again was about 80 in the shade and about 90 in the sun. Convertible top down and running around.
            I will get a digital gauge one of these days just for funsies. I'm just glad it's working quite well. I'll keep an eye one it. Thanks all for all the pointers.
            Last edited by silvernblack; 10-15-2018, 11:35 PM.


            • #21
              EggZackly! That's now totally credible good for you. The wired ones now harder to find did get last 2 on line check Amazon, Ebay like places for "Accurite" or "Taylor" is another name. Some home centers and the like just ask and I mean "wired" not wire-less is much more popular for household use. Roughly $10 items + if more features like memory of high and lows seen.

              Again it's because you can see both (different features on those too) inside and outside as in dash vent or clip to grille for what you need or are doing have live info to compare to norms especially for systems where info is missing. Best to record what finally worked best save that time later if you needed something or any reason to discharge and recharge again with right equipment can do year round almost any temp know at least that's right was always important and imperative on newer things there's just no range you need it to the ounce. Good luck with the project(s) this one and ongoing,
              MetroWest, Boston


              • #22
                Are you suggesting "wired" or "wireless"? I cannot ascertain from your comment above?


                • #23
                  What does "CCOT or TXV set up" mean? The hot rod a/c system uses a control valve (NOT an orifice tube). I'm guessing it means something like that?. This system also has a temperature probe that runs from the controls to the a/c "box".
                  Here are a couple of pics. I actually got that larger condenser to fit like a dream
                  Last edited by silvernblack; 10-16-2018, 11:25 AM.


                  • #24


                    • #25
                      WIRED as in has a sensor at the end or real wire some can take being submerged in water you decide how far to go.
                      Have tons of wireless ones are great check temps of air for shop and more inside and out of home freak out for freezing the shop need to know in Winter and so on. None are tools for automotive uses but can - that's all and wired is fast should be seconds.

                      A/C is so temp dependent on what you'll get at what pressures and other conditions it's just mandatory to me for fast info. Over some years many area shops just didn't have the time or setting to find where a problem was that wouldn't do it in front of them - I got those and had the time can't find or fix everything at certain locations.

                      Next is touchless infrared but isn't good to me to checking non solid air out of vents at all is a good clue of how much heat engine area parts are giving off heat and A/C lines pin things down.

                      The issue is knowing any results are correct so would have multiples of everything isn't practical for most,
                      MetroWest, Boston