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charge using subcool and super heat

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  • charge using subcool and super heat

    Saw a video of a guy charged his car, using subcool and superheat. Why is this not talked about? Looks very simple to charge. You are to be +/- 2 degrees between superheat and your subcool value to be properly charged.

    I bought one of those cheap scales trying to weigh the charge in. I guess if you never touched the charge hose and the scale, that would work. I charged my car like this and was off according to the sight glass. Not enough liquid refrigerant into the TXV. So weighing in didn't work. Waiting on a warmer day to try the superheat/subcool method. What do you guys think?

  • #2
    What vehicle using which refrigerant? Issue with newer is very low capacity systems. Just how to you add just one oz?
    IDK am disappointed with hose ends that you can't purge AIR out of. Just a little all bets off.

    Temps known exactly, performance temp vs incoming air temp - exactly.

    Seems default will be own a machine that counts how much comes out vs capacity then put back listed amount see if performance is right.

    If not issues with something else vulnerable is condensers over off season road debris or lines that flex evidence seen + on to other.

    Chances are superheat doesn't change where it happens if parts are clean, airflow up to a normal and correct charge.

    Home issue will be some loss if still working at all is low on refrigerant followed by DIY kits the line doesn't even purge keep doing that too much air - game will be over,
    MetroWest, Boston


    • #3
      I was talking about a guy that charged his car with R-134A, just like you charge your home AC system. He got within 1 degree of subcool with his superheat. Had 40F center duct temps at idle. Super easy method.


      • #4
        NO! Don't compare "stationary HVAC" to MOVING HVAC once MVAC. Whatever speed of whatever power plus constant changes in how "high side" can shed heat is almost never the same. Quantity to exact ounce will mater the testing it took was near always well thought out for all conditions possible.

        Vehicles get "radiant heat" backwards from engines, road heat plus speed vs wind usually overcome to not need to fan condensers. Get too close behind a "tractor trailer" is no wind for a spot and more beside one - ride a motorcycle you'll feel it.

        Onward - the pressures do not tell how much is in a system only that they are within expected norms when ALL conditions are calculated is a 3D chart not made.

        To tell you charge from empty + a vacuum to spot on ounces see if it behaves at all or what.

        Then find out if not right or as expected what is lacking usually is low on charge weight but don't just go adding any if that makes it worse you're screwed.

        Can't be short this is it's own area finding faults it's not a shotgun approach vehicles have no dipstick for charge if engine oil you'd only know starting from empty too - the idea is similar. Follow me?

        A house may just quit the vehicles can choke and self-destroy an otherwise OK system,
        MetroWest, Boston


        • #5
          Unless you have a newer heat pump stationary system that uses an inverter, stationary equipment has a fixed compressor speed and most often a fixed condenser fan speed, a car system all that varies all over the place, so conditions where subcooling may be high and superheat can vary with the heat load.
          Really apples to orange when looking at the two systems. The newer stationary systems are getting more complex than they used to be, esp when used as a heat pump where condenser surface area has to be larger to be able to function in colder climates.