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  1. #1
    Join Date
    Oct 2003
    Posts
    11
    i recently followed a refrigeration guy to get experience from the field since i just graduated in tech school. one thing is suprised me, when he was charging the system , he never use superheat, or subcooling method, or amp draw of compressor. he just used the sight glass or low side pressure to verify it's right charge. like today, he replaced water condenser #coax2076h for r-12 1hp walk-in freezer(design temp is 0F). he used hot shot to charge and clear the sight glasses. low side was 12psi high side was 175psi (he adjusted water regulative valve)when inside box temp is 14F.
    i was told by someone,if used hot shot to replace r-12 , never clear the sight glass, this would mean you are overcharge the system. the guy told me this is ok. so i am not quite sure about it. is he overcharge the system? is it high side pressure normal? (by the way, the water come out of comdenser was pretty damn hot). which direction is to increasing the head pressure for water regulating valve.
    can i used 10 td to calculated the low side pressure, like 14f(box temp) minus 10f td (estimated) is 4F then convert to psi to get low side pressure? is it the right way to do it?

  2. #2
    Join Date
    Apr 2006
    Location
    Indy
    Posts
    5
    Due to their temperature glide, it is not a good practice to charge any zeotropic refrigerant like Hot Shot, R409, R401, or any other 400 series gas, strictly by the sightglass. I regards to your TD question, email your question to David Callender (dcallender at icorinternational.com) He is a great technician and will either have the answer or find it for you.

    please put e-mail in profile, see this link for further details.

    (No e-mails in posts, due to site rules )



    [Edited by Senior Tech on 05-07-2006 at 12:12 PM]

  3. #3
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,542
    I have cleared every sight glass on all equipment I have retrofit or serviced for 15 years. If you cant clear the glass you have a valve problem or low head pressure...........................

  4. #4
    Join Date
    Feb 2003
    Location
    NH & Cebu
    Posts
    1,608
    I'm with you Freeze. Clear the glass. I've never had a problem. Sure, I may check TXV and comp superheat on a new startup. But to check subcool (with a receiver?) and superheat on every system I charge? How would I get anything done? When things are cranking, I'm doing maybe 8 service calls a day over a wide geographic area. I don't have time for that stuff.

  5. #5
    Join Date
    Nov 2005
    Location
    Laramie, Wy
    Posts
    709
    Originally posted by hvacmd2002
    I'm with you Freeze. Clear the glass. I've never had a problem. Sure, I may check TXV and comp superheat on a new startup. But to check subcool (with a receiver?) and superheat on every system I charge? How would I get anything done? When things are cranking, I'm doing maybe 8 service calls a day over a wide geographic area. I don't have time for that stuff.

    Nice to see a few guys speak the truth and give a little reality check. Never had a problem doing this either.

  6. #6
    Originally posted by hvacmd2002
    I'm with you Freeze. Clear the glass. I've never had a problem. Sure, I may check TXV and comp superheat on a new startup. But to check subcool (with a receiver?) and superheat on every system I charge? How would I get anything done? When things are cranking, I'm doing maybe 8 service calls a day over a wide geographic area. I don't have time for that stuff.

    Unless a man brings along a quality electronic thermometer and checks his readings over the entire system ... he is doing his self, his customer, his employer and this industry a DIS-SERVICE!

    The point of a service mechanic is to fix what he services, not just adjust the charge to suit his or her appointment schedule!
    I dont know you and I am not picking on you for any personal reasons.

    "Gas N Go" is NOT an acceptable method of charging any system.

    And the thing is, everybody knows that!



    Unless I knew the system well, from service on a regular basis, I could not "gas n go" unless I was about to replace the unit real soon.
    In that case, it would be acceptable to leave without doing a proper job.

  7. #7
    Join Date
    Jan 2006
    Location
    Near Atlanta, GA.
    Posts
    14,433
    Clearing the site glass worlks most of the time. Exceptions would be a system with a headmaster where it needs additional charge for low ambiant operation or certain piping designs where a clear glass does not insure a full column of liquid at the TXV.


  8. #8
    JD, not everyone knows what they're doin!

    Oh sure ... they may "get by" by charging a system "by the seat of their pants" ... but when you realise that any refrigerating system with our standard compressors ... they can live or die by the simple rule of thumb: 20 to 40 degrees of overall system superheat is the range they operate within.

    Outside of 20 to 40 degrees of NET superheat ... measured 6" from the compressor suction service vale ...

    Higher temp than forty and it will overheat.
    Lower than twenty and the flood-back will wash out the oil and kill the valves of the unit.


    I will wager a guess that MOST here do NOT follow that guideline rule.
    This is the type of stuff that seperates the mechanics from the hacks.

    For instance... when your about to install your manifold gage set onto a sealed system, do you inspect the needles to see if they are reading "ZERO"?

    Let's say your hi side gage is off ten pounds.
    No problemo you say. What's ten pounds of head pressure to a system operating over two hundred pounds?
    Sure ... I can agree with you.


    However ... the purpose of gages is to "SEE" what the refrigerant is doing inside the system.

    And when your gage reading is off by 10 PSIG ... your calculation for sub cooling measurement will ALSO be off!!!


    And THAT my friend, will result in you overcharging or undercharging the system by a very SIGNIFICANT amount!!!


    How would you like it if the doctor working on YOUR BODY was off by ten pounds on his measurements?
    How about your auto mechanic?



    When your watching a field service mechanic work ... and they have a set of gages in their hands ... if they dont have a temperature meter right beside them ... they should be about to fetch one.
    Otherwise they are NOT a refrigeration mechanic. They are just a guy who is in the wrong place at the wrong time.


    I'm sure a few here wont like what I just wrote. But that's okay.
    Dont like what I have to say ...? Just ask NormChris, Condensed Dave, Der Dice-Meister, IceMeister or some others here who DO KNOW what they are doing.
    Dont simply accept my word for this.



  9. #9
    Join Date
    Jan 2006
    Location
    Near Atlanta, GA.
    Posts
    14,433
    OK, we're talking about two different things here. Charging is one thing and adjusting the system for proper operation is a different step. Certainly things like superheat (at both places) are crucial to the proper operation and health of a system. But as far as getting the proper amount of refrigerent into a TXV/receiver/site glass system then clearing the glass will do it. Exceptions are as I mentioned above and I will add that if the TXV or other controls are badly out of adjustment a then charging to a clear glass will be problematic because they can give you an incorrect clear glass reading.

    [Edited by k_fridge on 05-06-2006 at 01:46 PM]

  10. #10
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,076
    This whole issue of whether to clear the sightglass or not and defining proper charging procedures with the blends comes up all the time. I blame it on the refrigerant companies like DuPont, Atofina and Allied Chemical (Honeywell) and their engineers who never get out into the real world of refrigeration for coming up with those totally inadequate and misleading rules.

    All of the literature out there from them calls for not clearing the glass but they don't explain why or qualify the statement with what type of system they're referring to......because either they don't know or they simply don't wish to confuse us simple people here in the field who work with their stuff every day.

    As k-fridge said, if you have a system with a headmaster type condenser flooding control you're certainly not going to leave a flashing sightglass when charging that system on a warm day.....if you know what you're doing.

    I do agree with their general guidelines for initially charging to 80-90% of the nameplate charge, but they don't say that's only for critically charged systems like cap tubes or TXVs without receivers. I suppose any more detailed criteria dealing with other types of systems would have been too technically confusing....so they decided to leave that out.

    What could be more simple than to say just charge a cap tube system to suction superheat, a non-receiver TXV system by liquid subcooling and a real refrigeration system by a full SG???

    If you just look at the temperature/pressure relationship of most blends on a T/P chart the first thing that hits you is the dewpoint/bubble point thing. That's an unfamiliar characteristic for those of us who cut their teeth on the likes of R12, R22 and R502. (Little did we know in those days that R502 was in fact a blend, but a near-zeotrope....so no bubbles and dew).

    For this discussion (rant?), let's look at the bubble point of today's blends. It's the point where the last of the blend component with the lowest condensing temperature becomes 100% saturated liquid. The other components have already condensed and are actually subcooled at this point as determined by the glide, or the difference between the dewpoint and bubble point. (Look it up).

    If we were to leave bubbles in the sightglass, what do we know?.......by definition at least one component of the blend is not fully condensed.

    Sure, I've read theories about the blends tendency to flash off a little bit when entering a SG and magically subcooling itself somewhere downstream. That is pure BS. Put your Fluke clamp on that liquid line just ahead of the SG and monitor your subcooling some day. If you still have bubbles (or even a river flow) in the glass you're not subcooled. That's not good enough for me and not acceptable by Mr.Sporlan downstream. Flash gas is flash gas.

    FLASH GAS, NO....CLEAR GLASS, YES

  11. #11
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,542
    Originally posted by R12rules
    JD, not everyone knows what they're doin!

    Oh sure ... they may "get by" by charging a system "by the seat of their pants" ... but when you realise that any refrigerating system with our standard compressors ... they can live or die by the simple rule of thumb: 20 to 40 degrees of overall system superheat is the range they operate within.

    Outside of 20 to 40 degrees of NET superheat ... measured 6" from the compressor suction service vale ...

    Higher temp than forty and it will overheat.
    Lower than twenty and the flood-back will wash out the oil and kill the valves of the unit.


    I will wager a guess that MOST here do NOT follow that guideline rule.
    This is the type of stuff that seperates the mechanics from the hacks.

    For instance... when your about to install your manifold gage set onto a sealed system, do you inspect the needles to see if they are reading "ZERO"?

    Let's say your hi side gage is off ten pounds.
    No problemo you say. What's ten pounds of head pressure to a system operating over two hundred pounds?
    Sure ... I can agree with you.


    However ... the purpose of gages is to "SEE" what the refrigerant is doing inside the system.

    And when your gage reading is off by 10 PSIG ... your calculation for sub cooling measurement will ALSO be off!!!


    And THAT my friend, will result in you overcharging or undercharging the system by a very SIGNIFICANT amount!!!


    How would you like it if the doctor working on YOUR BODY was off by ten pounds on his measurements?
    How about your auto mechanic?



    When your watching a field service mechanic work ... and they have a set of gages in their hands ... if they dont have a temperature meter right beside them ... they should be about to fetch one.
    Otherwise they are NOT a refrigeration mechanic. They are just a guy who is in the wrong place at the wrong time.


    I'm sure a few here wont like what I just wrote. But that's okay.
    Dont like what I have to say ...? Just ask NormChris, Condensed Dave, Der Dice-Meister, IceMeister or some others here who DO KNOW what they are doing.
    Dont simply accept my word for this.


    I do not carry around a thermometer for a service call.
    Fix the leak, clear the glass and go!!!
    What are you going to do if the head is 10 psig too high after you charge up a 1 hp unit????
    I will bet the next day when the load goes down it will fall in line! You cant tell me you check sub-cooling on all your calls r-12! No freeken way!
    On a/c units i check sub-cooling/ superheat as needed.

  12. #12
    Join Date
    Sep 2002
    Location
    South Dakota
    Posts
    6,579


    There is simply no way you can charge a system properly and accurately AND KNOW that it is charged right and has no other problems unless you have measured the;

    Low side superheat
    Condenser subcooling
    Air temp drop over the evap
    Air temp rise over the condenser

    Charging by sight glass and pressures alone is hack work.

    See my article at this link. Read the entire article or you miss the point. System problems are easily detected and identified during the charging process if you charge according to my article. I even check these same items on self contained systems where I know the factory weight and charge using a scale. Because when I leave the job I know the system is working properly.

    "If you don't measure, you don't know"

    http://hvac-talk.com/vbb/showthread.php?threadid=49522

  13. #13
    Join Date
    Dec 2005
    Location
    Rockhill South Carolina
    Posts
    370
    If you do not have time running 8 calls in a day to take all the necessary reading do you have time to go back @ 2am and do it.I got caught up in that rush rush go fast supermarket deal,its no good slow down some and examine everything and your call back rate will drasticly decrease.I know a little off topic you have a truck full of meters,gauges,and thermometers use them and learn how to see the story that they can tell you,if it takes 30 minutes longer who cares as long as you drive away and know that it is fixed and you have a happy customer.Also remember just because a man says he has 30 years experience does not mean he has been doig it right.

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