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  1. #1

    What went wrong?

    Thursday afternoon went to a call with a 40' long open bunker frozen food case that was down. Case and condenser are about 30 years old, running R408 for several years now. I found condenser cycling on head pressure, 1 of 2 fans was out. Replaced the fan motor, restarted, temps pulled down. Only problem, noticed sight glasses, (2), were flashing. Returned Friday around lunchtime and added 12lbs of 408, the receiver holds aprox 30 lbs. Glasses were still flashing, I was out of gas. There was ice on the suction line at the condenser, normal for this system. Store closed Friday nite at 8:30, temps were good. Saturday am, the on call tech called to tell me, during the night, case went down, lost all product. He said it was out on head pressure. He let "a little gas out", restarted system, and had good pressures. He then cleaned condenser coil, no change in pressure. Any ideas what went wrong?

  2. #2
    Join Date
    Jan 2010
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    6,232
    What was the high side pressure reading ?

  3. #3
    Join Date
    Aug 2002
    Location
    Southold.calm
    Posts
    5,616
    Quote Originally Posted by coolinginga View Post
    Thursday afternoon went to a call with a 40' long open bunker frozen food case that was down. Case and condenser are about 30 years old, running R408 for several years now. I found condenser cycling on head pressure, 1 of 2 fans was out. Replaced the fan motor, restarted, temps pulled down. Only problem, noticed sight glasses, (2), were flashing. Returned Friday around lunchtime and added 12lbs of 408, the receiver holds aprox 30 lbs. Glasses were still flashing, I was out of gas. There was ice on the suction line at the condenser, normal for this system. Store closed Friday nite at 8:30, temps were good. Saturday am, the on call tech called to tell me, during the night, case went down, lost all product. He said it was out on head pressure. He let "a little gas out", restarted system, and had good pressures. He then cleaned condenser coil, no change in pressure. Any ideas what went wrong?
    http://hvac-talk.com/vbb/showthread.php?t=158850

    We can’t see it so you need to be our eyes. Please post Pressures & Temperatures along with SH & SC readings.

    Get your post count up and apply for Pro status.

  4. #4
    I guess all the info would be helpful. Yesterday, before and after adding gas I was running 14/270. Ambient temp at the condenser was 86 F. The tech that went out this am said had head pressure 400+. After he took gas out he was getting 25/290 pulling down a hot box. I still had a flashing sight glass yesterday, his was clear this am. I didn't take SH or SC readings, I know, you don't gotta say it. We inherited this store a few years ago, and we put gas in most of the systems a couple times per year.

  5. #5
    Join Date
    Jan 2010
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    6,232
    Quote Originally Posted by coolinginga View Post
    I guess all the info would be helpful. Yesterday, before and after adding gas I was running 14/270. Ambient temp at the condenser was 86 F. The tech that went out this am said had head pressure 400+. After he took gas out he was getting 25/290 pulling down a hot box. I still had a flashing sight glass yesterday, his was clear this am. I didn't take SH or SC readings, I know, you don't gotta say it. We inherited this store a few years ago, and we put gas in most of the systems a couple times per year.
    So are you saying after adding 12 pds. of gas there were no changes in the pressures ?

  6. #6
    Join Date
    Oct 2008
    Location
    Winnipeg, Manitoba, Canada
    Posts
    105

    Pump down

    is it a pump down system? I've seen systems in the past that have undersized receivers so with a clear sight glass they can't pump down. They run fine until they make temp or hit defrost then go off on high head.

  7. #7
    Join Date
    Mar 2004
    Location
    Las Vegas, Nevada
    Posts
    1,647
    Went down in the middle of the night...? What type of Defrost?

    If Gas Defrost, I'd take a closer look at that. Also, if your CU has a Headmaster Valve...?
    The views and opinions posted here are my own. They do not reflect the corporate policies of my employer and will most likely get me fired at some point.

  8. #8
    This is the first time I've been to this board, and really want to thank all that read it. Adam, I believe you hit the nail on the head. I'm off today, but I couldn't stop thinking about it, so I just rode over there. The case is running fine, and the sight glasses are flashing a bit. The owner was there today, and after talking to her I learned that before we got the store, the case was 40' longer. They cut it off, and 40' of coil, to build a banquet room on the end of the building. Thanks again, I was getting a headache!

  9. #9
    Join Date
    May 2010
    Location
    Oxford, UK
    Posts
    336
    Did you fix the leak?

    Some of the blended refrigerants do seem to run with a flashing sight glass under certain conditions, R404A for example.

    It can be a good idea to try a pump down on a system after charging, will give an indication of if the system is over charged.
    Last edited by monkeyspanners; 09-25-2010 at 05:41 PM. Reason: nope!

  10. #10
    Join Date
    Apr 2010
    Location
    West Virginia
    Posts
    636
    if you add gas to a pump down system, you always have to make sure that it will pump down after adding gas.

    If the case is a long ways away from the condenser can easily overcharge.

    hot pull down, I never go for a full sight glass during the pull down stage because the expansion valve will be wide open (because of excessive superheat)
    and a lot of refrigerant will be in the evap.

    Jim

  11. #11
    Join Date
    Oct 2007
    Posts
    115
    [QUOTE=james122964;7930621]if you add gas to a pump down system, you always have to make sure that it will pump down after adding gas.

    If the case is a long ways away from the condenser can easily overcharge.

    hot pull down, I never go for a full sight glass during the pull down stage because the expansion valve will be wide open (because of excessive superheat)
    and a lot of refrigerant will be in the evap.

    Jim[/QUOTE This is very true i learnd my lesson the hard way as well !

  12. #12
    Join Date
    Sep 2010
    Location
    PA
    Posts
    14
    I have two problems with this whole thing. First you say your company has been adding freon to the system every year. Also What made you think the system was low on freon when you found the problem with the fan motors and then the system worked after replacing one. I have a lot of systems with blends that don't run a full sight glass. These days there are many other factors involved with finding the correct charge. Also why aren't you finding and fixing the leaks. You might even have noncondensables with it being a pumpdown system if the leak is on the low side.

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