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  1. #1
    Join Date
    Apr 2010
    Posts
    92

    Charging to full sight glass?

    Ok, ran into an odd one. Typical call for a large WIF down. On roof, sight glass barely showing any refrigerant. Electronic leak check, found two leaks: One at low pressure control, other in suction line vibration absorber. Since it was in a major downpour, I gassed up for now to a full sight glass. The unit is listed at 33lbs of 404. I only had to add 5 lbs and told them I'd return.

    Now, I had soaped up the vib absorber and it bubbled pretty good, but I figured it'll hold for a while until I return. But they called back the next day saying the unit was down already. Ok, I figure the vib absorber was probably leaking worse when the unit was running (checked while it was idle due to the condenser fan blowing all over). Another tech returns to complete the job, and I wind up meeting him on site after he's 90% done. He pumped down unit, changed drier, changed vib absorber and pressure control. He was in the process of adding gas. Sight glass clear after 6 lbs. Unit coming down in temp. Time to wrap up.

    Then the sight glass started bubbling again. I figure the evap fans just came on, so lets add a bit more. Another 2 lbs. Ran clear - then about 10 minutes later, just as we were wrapping up AGAIN, started bubbling again. Ok, add another 2 lbs. Ran clear again, and slowly started bubbling AGAIN. So we started doing a more thorough leak check, using two electronic leak detectors and ran across every inch of tubing. I figure a leak that big should be blowing our hair back. But found nothing. It seemed we had to keep adding gas to clear the sight glass. After about an hour, and another 6 lbs, it finally started to stay clear.

    Is this unusual, or common for a system with such a large receiver? Unit does have headmaster, so its possible that wasn't opening as well.

  2. #2
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,543
    You need to look at how your head pressure is controlled. What was the temperature where the condenser is located.
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  3. #3
    Join Date
    Mar 2002
    Location
    fort walton beach fl.
    Posts
    782
    The txv could have been opening and closing, I would verify that the txv is the correct size and the bulb is mounted correctly. Also, with a headmaster. You will need to add additional refrigerant after the sight glass is clear. I believe its an additional 20%, but I would check with the condenser manufacture.
    http://acfwb.com/

    "The best preparation for good work tomorrow is to do good work today"

  4. #4
    Join Date
    Aug 2012
    Location
    willowick ,oh
    Posts
    257
    You said its a 33 lb system. If it has a headmaster you were probably just low on refrig. It depends on the temp outside tho. Need all of the numbers to be sure. , sc idt odt delta, pressures. things that matter. You could have a 15 lb reciever on that pig or bigger. Your headmaster is gonna compensate for a low charge until you have some juice in the reciever.

  5. #5
    Join Date
    Jul 2012
    Location
    Western KY
    Posts
    1,221
    Your still low. Like already pointed out you should have a good sized receiver. If its warm out your glass will fill but receiver will be empty so when headmaster starts throttling all your liquid gets stacked in cond coil and glass will start flashing. You can, and I would pull the charge and weigh it back in. Or keep guessing at it and give yourself grey hair. That's where mine came from.

  6. #6
    Join Date
    Aug 2012
    Location
    willowick ,oh
    Posts
    257
    Quote Originally Posted by Tommy knocker View Post
    Your still low. Like already pointed out you should have a good sized receiver. If its warm out your glass will fill but receiver will be empty so when headmaster starts throttling all your liquid gets stacked in cond coil and glass will start flashing. You can, and I would pull the charge and weigh it back in. Or keep guessing at it and give yourself grey hair. That's where mine came from.
    I absolutely agree that the factory charge is the best way to do it. Also avoids the nuisance call-backs. Definately been there. Good call tommy

  7. #7
    Join Date
    Mar 2009
    Location
    Mid-Mo
    Posts
    3,425
    I haven't seen a nameplate charge on any of our refrigeration units. Agreed with everyone else that it sounds like you're still short on happy juice.

  8. #8
    Join Date
    Jul 2012
    Location
    Western KY
    Posts
    1,221
    Quote Originally Posted by ryan1088 View Post
    I haven't seen a nameplate charge on any of our refrigeration units. Agreed with everyone else that it sounds like you're still short on happy juice.
    Me either. Figure someone had wrote it on there from previous service. I usually do that myself on a service card or log book.

  9. #9
    Join Date
    Sep 2007
    Location
    NH
    Posts
    1,110
    Yep add the flooding charge after the glass is full AND system is almost at set point.

    Your evap coil will use much more refrigerant as it get cold, as less refrigerant is boil off and the coil is more flooded..... Unless your TXV is grossly oversized.

  10. #10
    Join Date
    Jun 2009
    Location
    NYC
    Posts
    422
    Forget the sightglass, charge by subcooling it's to only way to tell if the system is fully charged.
    I use the sight glass for the moisture indication only.

  11. #11
    Join Date
    Sep 2007
    Location
    NH
    Posts
    1,110
    Quote Originally Posted by keviekev70 View Post
    Forget the sightglass, charge by subcooling it's to only way to tell if the system is fully charged.
    I use the sight glass for the moisture indication only.
    Wrong... Forget subcooling when you have a receiver. Subcooling is what it is just fill the glass and add winter charge if needed.

  12. #12
    Join Date
    Sep 2007
    Location
    NH
    Posts
    1,110
    I would agree with you on a cap tube unit or a system with no receiver subcooling needs to be checked for proper charge through.

  13. #13
    Join Date
    Oct 2012
    Posts
    10
    I know a lot of times when charging a large system, the sight glass gets clear and then will start bubbling again. I charge through the low side, and flash off the refrigerant in my gauges as a liquid, let the compressor pull it in. As it gets through the condenser and receiver, the sight glass will show a solid column of liquid for a little bit, and then once more vapor gets back to the compressor, it will show more bubbles. Just keep an eye on it and see, if you didn't find any leaks, chances are there isn't a leak that large.

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