Charging an A/C system in winter

    I am planning on having my heating/AC system replaced soon. Is it possible to charge the system with R22 EFFECTIVELY with the outside temperature at about 50 degrees F? I realize there is a way of calculating an amount of Freon to be loaded, but can the system be checked for optimum charge while the temperature is so low??? Or must it be rechecked later when the temperature reaches about 80 degrees? Thanks.
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the charge will be weighed in with a scale. i've seen that some units nowadays have a pre-charged system with piercing valves that release the refrigerant into the system,after the lines are evacuated.

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I would think it would be easier to charge a system when the temp is low, because it wouldn't require as much pressure. (as much freon, but not as much pressure.) Whatever they charge it from has more pressure than the house does, summer or winter.

They have formulas. Boyle's general law of gases, or something like that.
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iirc the suction formula is the ambient temp converted to psi (on a press/temp chart) minus 30 psi.
they can also partially cover the condersor to simulate warmer conditions.
wrote:

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tom&kel wrote:

Either you don't "recall correctly" or somebody pawned a bogus formula off on you. That one is worse than a WAG.
Richard Perry

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it's been about 5years since i've put my guages on anything bigger than a cars a/c ,so it's probably my memory. wow! did i booger this up....
the formula is in my carrier transport technician repair guide. it states that this "rule of thumb" is acceptable; ambient temp plus 30 degrees converted to psi for the specific refrigerant on a pt chart for an approx discharge pressure.
the refrigerant level was checked by covering condensor untill pressure was at 260-280 and then look at the bottom sight glass to see if it was full and the top one was empty.
btw....what is a WAG?
wrote:

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tom&kel wrote:

That method was never correct. You can't charge a system by discharge pressure.

Maybe you can pick it out :) http://www.acronymfinder.com/af-query.asp?String=exact&Acronym=WAG You may have to scroll down the page.
Richard Perry

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wrote:

Actually this is completely the opposite. youi can't charge it accurately in cold weather due to the low pressures. +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ spam protection measure, Please remove the 33 to send e-mail
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Mine was installed in winter then the tech recomended he come out in spring to start and check it, he did.
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--------------------------------------------------- even charged with the scales,or pre-charged do you come back and double check in warmer temps?
i did transport refrigeration straight outta tech school and my service manager never once told me to have a recheck(not like a customer from texas,or wherever, would travel back for a check up).
did three years with him, and never wanted to do refrigeration again....
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Charging in the winter is best done by weighing in the charge, when starting with an empty system. Most manufacturers publish pressure charts for the winter, but they are not very accurate, due to differences in indoor air flow and indoor and outdoor conditions. It is best to check charge in cooling season with outdoor temps at least 75 degrees. Charging is then done done by subcooling for expansion valve systems and by suction superheat for piston metering devices.
When charging in the winter, pressures in the system are lower, but pressures in the refrigerant drum are also lower.
When you charge by weight, you must know the charge for the outdoor unit and indoor coil, as well as the refrigerant line length and tubing diameter as they affect correct charge as well as the units.
It is just best to check it in the cooling season when there is load on the system. It is best to let it run 15 minutes to let the temperatures and pressures stabilize.
Stretch
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Stretch wrote:

    Thanks to all who responded. I thought it could be done "Roughly" in winter via the weighing method, but to be done accurately it must be done in warmer weather. I just like to know what the proper procedure should be so it is done right. Thanks again.
Ken
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neat... i haven't touched a residential unit since my lab class in 99.
when we did a transport unit repair or check of unit at work, we would partially cover the condensor to raise the pressure if it was cold. if it was a new install or complete recharge, it would be weighed in. didn't have much use for line size or length due to everything being in one small area ,unless it had multiple evaporators. running unit in heating,then cooling was the load like you said.

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Ken wrote:

The system can be charged correctly at 50 without recovering the existing charge and weighing in. In order to charge the system correctly at this low ambient the condenser airflow must be restricted or reduced by some means, in order to simulate the maximum ambient temp that will be encountered in your area. Very few techs do this correctly however, if at all, so you'd be better off waiting for warmer weather IMO.
Also, I advise strongly against the weigh-in method on fixed orifice systems, since the charge is very critical on these systems. There is no way to calculate the correct charge, since there are too many variables to account for. You may find rules of thumb in the literature, e.g. X lbs of refrigerant per ft of 3/8 copper tubing, etc. but these engineering formula can only be applied reliably under lab conditions. OTOH, a TXV metered system is much more forgiving when it comes to refrigerant charge. On these systems weighing in the charge would typically be adequate, but only a fool would go through the trouble of recovering the charge to do this since setting the correct charge on a TXV system is a simple matter of adjusting the subcooling of the liquid line, which BTW must be checked even if you have weighed the charge in.
Richard Perry
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it
outside
be
Or must

degrees?
The system can be charged but due to the cool temps, it may not weigh the same in the spring. Often units get overcharged when replaced in winter. Your installer will be happy to come out and make an adjustment in the spring when you start using the A/C. It doesn't have to be 80 out. 60-70 is ideal.
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Kathy wrote:

Because it wasn't done right.
Your installer will be happy to come out and

It doesn't have to be 80 out, but I disagree with your last statement. Why do you consider the 60-70 temp range to be ideal?
Richard Perry
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After I clicked send I rethought that 60. I amend my reply to say "In the 70's would be ideal". Because it is warm enough to get the A/C to operate and not so hot that it is constantly running.
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Kathy wrote:

The ideal ambient temp for charging an air conditioner is the temp at which the tech doing the work is the most comfortable :)
Richard Perry
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