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  • #16
    My understanding is the oxygen in air can attack rubber under heated conditions, and that nitrogen is more neutral. It must expand and contract, otherwise internal combustion engines wouldn't produce any power, the oxygen and fuel burn to produce heat, but it is the 78% of air that is nitrogen that does the bulk of expanding when heated to produce power.
    oxygen is highly reactive esp when hot. They've used nitrogen in hyd accumulators and aircraft struts for as long as I know. Not surprising automotive puts it in shocks and tires now. Not sure its work it in tires. I know the big industrial gas companies started 1st putting it in tires. but I don't see any gain for the cost. I run my truck tires thru 3 treads (original, and 2 caps) and by that time the casing is shot, I don't see where nitrogen would help any?
    As to temps, I don't see it that cold often, but do get into -25 to -30 every once and a while. Those are air temp and not 'Wind Chill" numbers. You better be well prepared for it. It funny, once it is below about -5, I can guess the temp by how long the vapor trail is coming out of my exhaust stack. AT -25 it is longer than the trailer and at -30 it is about 2-3 times as long!

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    • #17
      Oh my Cornbinder89. What a LOT to rethink and what tolerates the extremes. So true about the vapor trail as a clue almost have to dang temp measuring things quit working anyway in and around those extremes!
      Tom
      MetroWest, Boston

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      • #18
        Well, after mid-week temps where the high temp stayed well below zero, today is hovering in the upper 30's, warm enough for the frost switch to turn on the compressor, so I charged the system. According to my calculations, converting from the R12 charge, to the 134a, it should take right around 3 12 oz cans of 134a.
        After evacuating the system, I put 2 1/2 cans into the receiver in liquid form (compressor off), then the rest of the last can with the compressor running in vapor form into the low side port.
        This is my 1st attempt to charge a system in this low a temperature. While it is far too cold to assess how well it will cool, I think I was successful. I had the condenser covered to build some heat into the refrigerant so the compressor would run long enough to draw the remaining vapor from the last can. One thing about charging this way, it almost completely empties the cans when in liquid charging, my hand heat was enough to build a little pressure in the can, the system was cool enough that condensing pressure is around 35 psi, and if the can is warmer, almost all of it enters and stays liquid.
        When I built this system I added another set of ports, the originals are on the compressor manifold, a high side at the drier, and a low side on the outlet of the evaporator. This allows me to charge in the liquid state without worrying about slugging the compressor when it is turned on, by putting the liquid right into the receiver.

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        • #19
          Good for you. Sure was watching actual temps nothing for the low 'actual' air temps you had but the wind was insane. I was having trouble keeping shop up to 60 nothing for A/C going on all other stuff.

          Went thru this once now quite some time ago mostly because it was possible to get shop, all the metal of tools and equipment all plain hot. Truth is just the proper charge and prove that it working did take way too much time but just had to prove it could be done.

          Seem to be out of the sub-zero nights still long nights a memory remote says it did touch 33F today but nothing really melted ground takes time,
          Tom
          MetroWest, Boston

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