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Systems pressure with variable O tube

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  • Systems pressure with variable O tube

    Should the systems hi & low pressure with variable O tube be about the same as with a non variable O tube system? What about at idle and at 1500rpm?

    Thanks again

  • #2
    Hmmm? Never used those. Archived in original forum even those in the trade were not so crazy about those. One comment was somehow it was noisy? Anyone want better performance not sure that will do it or changes in what we think as normal for pressures. If faster cooling for stop and go or from a hot engine start up cooling the condenser is the way or any improvements for more exchange of heat,
    MetroWest, Boston


    • #3
      I am no expert on OT systems, but the physics of how a refrigeration system works remains the same. So that being said the low side should remain constant in the high 20's to low 30's for the coldest evaporator.
      So what would a variable orifice help? Well if the engine is turning slow (slow compressor speed) and the OT is a little large, too much refrigerant will pass thru the evaporator and vaporize in the evaporator and accumulator, so the low side will be higher than ideal and the temp will be warmer than ideal. Conversely, at speed if the OT is smaller than ideal, not enough will flow into evaporator and it will all boil before the outlet and less cooling will occur.
      So from what I can see, the variable OT will act like a smaller tube at low speed and a larger tube at high speed. The pressure ( at least the low side) will remain the same, around 28-32 psi over a broader compressor speed range that a fix orifice tube. High side might be slightly higher at low compressor speed than with a fixed OT.
      Someone may prove me wrong, but that is how I see it.


      • #4
        Can't prove you wrong CB89 :-)
        Right now all my own are CCOT (w Orifice tube) do hold enough volume of refrigerant are pretty good. Colder fast with a cold engine and speak for my own anyone knows best. They both are slow with a warm engine like a quick 10min stop then if slow into traffic for example slow to cool off watching it live at a vent. It comes down almost no matter how hot outside (watching that too) to at least mid 40s can bump down for a quick time at say 38-39F isn't supposed to snaps right out of that.

        Both use thermostatic (bi-metal spring) fan clutches that ARE KNOWN WEAK a want them that way?? Too much pull they roar is annoying to me - that's all and waste of fuel + loss of power taking off. I'd rate both as very good and temp gauge never moves from the same spot mega hot out or dead of winter below zero as the layout should do.

        Not sure where you would gain if it tried to throttle size of OT never would mess with near perfect. Just maybe a small volume system for load on vehicle you would get some benefit kind of acting like an X valve?

        Already said never used one and don't expect to OE would have if it was better and that simple IMO,
        MetroWest, Boston


        • #5
          Tom, you have a point about if it was better, MFG would have used them.
          In trucking there are many things marketed to truckers to "fix" problems that don't exist. Disk wheels on large semis went from "stud pilot" where the wheel is centered by the nuts on the studs with a ball seat, to "hub pilot" where the wheel stud hole are loose fit, and the wheel is centered on the center hole via lands on the hub. There is a big market selling devices to "fix" the problem of the stud hole not being a tight fit on stud! All to fix a problem that isn't. Hub piloting is much more accurate than the studs could ever be.
          One thing about A/C systems, they are generally "free floating" systems so when you change one thing, everything changes until it finds "equilibrium" again. It can drive you mad if you try to impose too much manual control to "fix something" and cause more problems as the system reacts to the change.


          • #6
            CCOT can work fine but if a must use a TX set up. Dual air does the rear TX steals the bounty when low charge and can't (I can't) get reasonable pressures with both on just use fronts.
            Anything made but A/C in a vehicle now that they've save on real outdoor air vents to floors, vent windows up to no key for passenger's side is a treat with dead remote battery or vehicle and 2" of ice over driver's side! On rant about that stupid move.

            A or B with an "O" tube. If it worked better they'd either downsize all parts, components and save or use it stuff like great A/C sells cars and by the millions what would an O tube cost is next to nothing for either.

            I'd freak with your big rigs not a chance I could so much and handle the weight of a wheel probably not just the tire off the rims!

            Back - it was quite some time ago maybe GM Tech at the original site said they could rattle making noise maybe only when shut down?

            Said here already and again only a couple vehicles made new A/C was plain inadequate all older now. Corvette with CCOT the metal hoses are so close to red hot exhaust just nothing you can do there's no room either? That and rear or mid engine air cooled with condensers just all awkward just one look - "This isn't going to be good" and it isn't.

            In all fairness I'm from where sign off says and always. Have been all over Summers too insane heat of AZ no shade! All but highways have shade around here except right now sun is highest it gets can sneak a high angle - it matters a lot.

            If anything already said boost the condenser, fan(s) or when possible a better condenser. Next if a humid area I would use condensate water and catch it to mist up front - home units do that now unless you specify not to. Nothing cools a condenser like evaporating mist all over it as we see just testing with a hose on almost anything.

            In short this fix or help for A/C isn't going to be recommended by me just go OE type and color unless it was optional for another size would have to look that up,
            MetroWest, Boston


            • #7
              For many years, Big trucks either didn't have A/C as a option or many of the companies didn't spring for it. Then the Teamsters got A/C written into the contract. Aftermarket roof top units and back wall units were popular. Also some big companies opted to order without A/C and then fit the aftermarket units before they were placed in service. That way not matter what truck brand, all the truck took the same A/C parts.
              Roof mount condensers were really popular as it placed the condenser well above the hot blacktop, and it got plenty of cool air up there, with the added benefit that there was nothing in front of the radiator to impede engine cooling.
              Dis advantage of roof mount A/C was roof leaks over time, which was partially cured by just mounting the condenser on the roof and the air handling was mounted on the back wall of the cab (split system).
              By the early 80's A/C was pretty much standard on trucks and the roof mounts started to go way. There are still made and used, you see a lot of them on locomotives. There roof leaks aren't a problem as the roofs are steel plate, not sheet metal. I was surprised to learn that A/C is not std in locomotives, that the big "main line carriers" all have it but many of the smaller line do not, makes for a hot day!


              • #8
                VAND - First off sorry for carrying on about A/C and more about it in general. For you think about not using the Variable O tube.
                CB89 - TMK and not available to work on UPS, USPS vehicles for local delivery didn't or still don't have A/C at all rather a fan on dash and issued shorts. If you don't like it that isn't for you.

                High end vehicles (my small world but was seeing it all the time on Cadillacs early for STD climate control A/C was 1/3 the cost of the cars! Lots ordered cars without got a credit option on the window sticker price and up to 8 windows that moved, real vents worked fine.

                Schools and school buses never had A/C not sure they do now but wouldn't know for sure. If that hot and can be schools closed that day.

                Trucks, trains and such clearance for high or roof mounts fine but may limit where you could drive and roads said so! Know your height or bridges took those right off. Passenger trains (never use them myself) I think used ice and fans - yes ice cut from lakes (huge blocks) stored in ice houses packed in hay and sawdust lasted all Summers till cold again!
                No joke on that.
                Store more perishable foods in a basement the ground here and many places never warms up that much always cool.

                Ice cream was easy before any refrigeration! Yes - try this test yourself now: Take a glass with packed ice and some water. Measure the temp with a meat type thermometer. Now salt the heck out of it and stir it keep adding said to melt ice faster and faster. Watch outside condensate start to frost up on the glass and the temp! You've lowered the temp of both the ice's temp and inside where you forced it to melt without pressure!

                Change of state from solid to liquid is no different that from liquid to vapor it "removes heat" without using pressures.

                Shade tree? A real good one leaves are evaporating moisture in direct sun and staying cool the air drops down under them below air temps around it! Not just sun direct on a surface like YOU or solid ground. If it does that all day that heat rose so much it can make a late day rain with the water it took. Magic!

                Head for the ocean beach? Land heats up daytime water is cold comes in under that is cooler as the hot air rose can reverse that at night so automatic temp moderation.

                Homes/building had high roofs with window let air out during the day open lower levels airflow came thru we call "breeze ways" so things were pretty clever before all this fuss!

                If way too hot well water is cool so did need to wet down animals or might lose them.

                Laugh - why did we complicate so many things that were already solved? :-)
                MetroWest, Boston