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Its been getting cold out

Hey everyone I'm a new guy to the trade (2 months in) and live in the northern regain of the us. I was wondering when it gets this cold out how can you charge a refrigeration unit or Air conditioning unit that has to be running all year round and is outside in the low ambient conditions?


  • Spence
    Spence Member Posts: 316
    Low Ambient Charging

    The ONLY way is to weigh in the charge. For example, the outdoor section of a residential split system is stamped 6 lbs./5oz. of refrigerant. This means that exact amount is adequate for the outdoor coil, the smallest AHRI rated indoor coil for that unit, and 15' of tubing. If you have a larger coil or longer tube set you need to add "x" additional refrigerant. The additional charge amount is found in the IOM manual or make a call to the distributor's technical department for help. If you do the proper weigh-in, provided your air flow is within factory tolerances, you will be close enough to not have to worry about the unit's performance. When the ambient rises to a temperature that allows customary charging, use the chart inside the OD unit for proper temperatures and pressures. And, as always, check your air flow, superheat, and sub cooling.
  • Probie
    Probie Member Posts: 7
    edited December 2013
    ONLY way…?

    i have read in the modern air conditioning and refrigeration book about weighing in the charge as you have explained, but my step father is in the business and i asked him he said he turns the condenser fan off to raise the C.T. to 95 degrees so you can charge properly. i have also asked other people outside of heating help and they have also told me other ways to raise the C.T. so you don't have to always weigh in the charge. ex: putting cardboard on the sides of the condenser or a tarp. i have also seen in a fieldpeice brochure what they call a charging jacket (in the low ambient charging section) and that goes over the top of the condenser and keeps the same air circulating in the condenser to raise the temp to 95 degrees or so. I appreciate the info on just another way to charge during the winter, but as for there being only ONE way i have to say that i disagree with that.


    That is the link to the fieldpiece page for the charging jacket i think its a really cool new item to help all mechanics in the trade charge during low ambient temperatures!
  • Techman
    Techman Member Posts: 2,144
    edited December 2013
    charging AC units

    Merry Christmas to ALL!  This AC charging subject, in every kind of weather conditions, has come up several times. While I do agree w/ Spence that the weight charging method has its advantages , I disagree that the weight charging way is the only way. There are several ways of charging a system, properly!

    If the refrigerant charge is stamped on the unit nameplate and that charge is rated for 15' , then does the SubCooling rating that is also on some nameplate's also derive from that same 15' of line set? Welcome to the trade Probie!
  • Spence
    Spence Member Posts: 316
    LA Charging

    Show me an IOM that recommends a charging jacket, blanket, newspaper, etc. that isn't 20 years old. Convince me that a "band aid" that blocks air flow is what your maker recommends. Prove to me that weighing in, which is what your manufacturer wants in low ambient temperatures, is not the most accurate, or all packaged units would not come pre-charged. Sub cooling remains the same as long as the tubing length is within tolerances and you've added the proper additional charge.
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,225
    So here is

    A million dollar question. What if it is a mismatched refrigeration unit and there is no manufacture data available. Specifically, a commercial walk in cooler operating on R-22 and another one running on R-404

    How is one too accurately calculate the proper target sub cool?
  • Techman
    Techman Member Posts: 2,144

    How can the SubCooling be the same for a 15' lineset that has a 10' vertical rise , and a 50' lineset that has a 30' vertical rise?

    In refrigeration work , I don't recall very many times that a given SC is desired and tried to be reached, as compared to simply having a full liquid line at the TXV and the resultant SC is what it is! Assuming  ,normal ,stableized operating temps and pressurers. So why can't the same hold true for refrigeration and AC
  • Techman
    Techman Member Posts: 2,144
    edited December 2013
    cold out

    Hi David. I do agree charging a res AC in 75* or higher is a nice way to do it. But, here in L.I. N.Y. we don't have that many 75+ days in September-May. The TinKnockers that I do the refrigeration part of Res AC's for, WILL ONLY PAY when the job is done. So I hand them a bill for a completed job, AC work is just hi temp refrigeration to me!  Every mfrg of TXV's require a full liquid line. Been doing the 1 Tin guys work for 30+ years, must be doing something not wrong , right?

    Now, back in the day it was much harder to properly charge the orifice type metering device systems in low ambients.
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