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  1. #1
    Join Date
    May 2009
    Location
    Baltimore, Md
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    34

    Controling superheat to check hot gas bypass

    Looking at an ice machine today, very vague i know but, checking sh and sc off the chart so to speak sh about 40-50 subcool negative 40-50. Way udercharge Im thinking so I add bout ten percent of factory charge along the way hoping to see sh come undercontrol and sc get positive. no, was able to get superheat lower and lower with additional charge but sc still in the neg 30 range. I said compressor at first but now im thinking hot gas by pass leaking....because txv should have limited superheat yet I was able to get it below five.. I did this, I think by forcing more refrigerant into system around the txv if it were not the hot gas bypass then txv should have controlled superheat instead it was directly proportional to charge. Is this correct ? I know its probally easier to just check delta t across valve but I left befor I could think of that.

  2. #2
    Join Date
    Jan 2010
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    6,239
    Did you check to see if the solenoid was receiving power ?

  3. #3
    Join Date
    Nov 2007
    Location
    Mississippi
    Posts
    1,338
    What kind of ice machine is this? When on a service call for ice machine, I usually check delta T on hot gas bypass, verify operation of condenser fan (if air cooled), verify H2O fill valve shutting off. I would check all this at a minimum before I started adding refrigerant.

  4. #4
    Join Date
    May 2009
    Location
    Baltimore, Md
    Posts
    34
    I should have, but did not. That would indicate an electrical malfunction because it was in the freeze cycle and should not be energized. Pressures were almost equal about 80's on low and 90's on high, you think that valve is wide open?

  5. #5
    Join Date
    Jan 2010
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    6,239
    Quote Originally Posted by coldmark View Post
    you think that valve is wide open?
    If so the line would be warm on both sides of the valve.

  6. #6
    Join Date
    May 2009
    Location
    Baltimore, Md
    Posts
    34
    socotech is right I should have not added gas without being more thorough. I saw oil on the refrigerant plumbing and looking at the numbers, thought leak, when it couldnt pull down low or pressurise high after 10 percent more charge I thought compressor. I only do a few ice machines. mostly I do med temp and they dont have hot gas valves so I was in somewhat unfamiliar territory. Condenser fan not coming on because of low pressure on high side eventually it does though. I guess a leaking or open hot gas bypass can look like a weak compressor. From now on every ice machine gets a delta t on bypass valve. I checked for water issues fill valve is shutting off but water sump is cracked and leaking slightly like its been for many months with acceptable ice production, this is a new problem

  7. #7
    Join Date
    Nov 2007
    Location
    Mississippi
    Posts
    1,338
    Leaking bypass would cause low head, high suction, condenser fan to cycle. Oh and of course.....no ice.

    I also like to put a pocket thermometer in sump, if possible, just to monitor progress. A properly operating machine will usually start at about ambient, then steadily pull down to 32* until harvest begins.

  8. #8
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,330
    Quote Originally Posted by coldmark View Post
    socotech is right I should have not added gas without being more thorough. I saw oil on the refrigerant plumbing and looking at the numbers, thought leak, when it couldnt pull down low or pressurise high after 10 percent more charge I thought compressor. I only do a few ice machines. mostly I do med temp and they dont have hot gas valves so I was in somewhat unfamiliar territory. Condenser fan not coming on because of low pressure on high side eventually it does though. I guess a leaking or open hot gas bypass can look like a weak compressor. From now on every ice machine gets a delta t on bypass valve. I checked for water issues fill valve is shutting off but water sump is cracked and leaking slightly like its been for many months with acceptable ice production, this is a new problem
    Oil? That's what a leak looks like. Find it, fix it and recharge properly by the book.

  9. #9
    Join Date
    May 2009
    Location
    Baltimore, Md
    Posts
    34
    Yep high suction low head cond. fan not cycling though. After a long delay when high side heats up n pressurizes enough it will come on seems to stay on didn't stay for a harvest though, owner told me it averages an hour or more. I'll check by pass next. If valve were leaking would there be any harvest?

  10. #10
    Join Date
    Jan 2010
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    6,239
    Quote Originally Posted by coldmark View Post
    If valve were leaking would there be any harvest?
    That would be a full time harvest. There would be no ice to harvest.

  11. #11
    Join Date
    Nov 2007
    Location
    Mississippi
    Posts
    1,338
    Quote Originally Posted by coldmark View Post
    Yep high suction low head cond. fan not cycling though. After a long delay when high side heats up n pressurizes enough it will come on seems to stay on didn't stay for a harvest though, owner told me it averages an hour or more. I'll check by pass next. If valve were leaking would there be any harvest?
    No. If bypass leaking, there will be no harvest because there will be no ice. No ice = ice sensor probe not shorted to initiate harvest (or whatever type you have). Do you remember what type/brand machine it was?

  12. #12
    Join Date
    May 2009
    Location
    Baltimore, Md
    Posts
    34
    well saw that oil before when it had a faulty spdt power switch. I haven't seen many leaks without the telltale oil so we think alike icemeister but its plenty charged superheat is dangerous low. So if it has a harvest but just takes forever then weak comp. if it never harvests then leaking valve, I'd love to hear its that simple especially cause I already said it was ineffiecient comp.

  13. #13
    Join Date
    May 2009
    Location
    Baltimore, Md
    Posts
    34
    I feel like a hack cause I am posting without equip. data. Ice sensor is the bridge thickness type where water runs over hindged sensor and initiates harvest. I forgot to mention this machine its in its twenties. A while back I adjusted the sensor to compensate for ice bridge thickness variation due to temperature glide in evap with 414b its an old r12 and some other charged it with hotshot, maybe when that oil showed up. Its not freezing the evap. If there would be no harvest with a leaky valve then Im still thinking comp. cause it does harvest just takes forever.

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