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  1. #1
    Join Date
    Dec 2011
    Location
    louisiana
    Posts
    58

    why did this unit freeze up

    Appreciate some help here , first here is the info, I've been here long enough to know you guys want a lot of data:15 year old , r-22 ,1 1/2 ton rheem split,orfice, low side pressure 68, SH 5.6, T1 46, high side pressure 284, SC 38, T2 88, ambient 95, current draw in range 8.4 amps. Inside at return - dry bulb 77 wet 63, supply - dry 67 wet 53, small 600 sq ft apartment, unit in central hall closet with short supply in furred down ceiling ( 12 unit complex I own , so I have other units to compare data with) PROBLEM - mowing yard and find this unit with suction line ICED up outside -- Been thinking head was a little high in earlier checks ( taken 4 previous readings in 2 prior months, all readings near above), so I cleaned condenser coil --(after cleaning and unit off awhile, I checked line temp 81 against line pressure 147 which made me feel no non condensables in system) when running ,no drop across filter/dryer either. After cleaning, low side barely changed, high side dropped 10 PSI, all else almost same (SC, SH, T1 +T2) - SH says low charge, pressures seem fine- SC says...I don't know :readings taken at valves with my testo 550 . Unit was unoccupied for a week and stat set around 80 when freeze occurred. Any constructive ideas appreciated.
    Thanks
    Greg

  2. #2
    Join Date
    Jul 2005
    Location
    Boston/Cape Cod
    Posts
    66
    Getting good air flow in air handler,indoor coil clean, is filter in place and clean?
    southshorejohn

  3. #3
    Join Date
    Dec 2011
    Location
    louisiana
    Posts
    58
    knew I would miss posting something, clean evap and filter, good airflow, no leaks in duct (furred down supply) or return, dr pepper in refrigerator, shower rod in bathroom... oops got carried away there

  4. #4
    Join Date
    Jul 2005
    Location
    Boston/Cape Cod
    Posts
    66
    do you have od dry wet temps? With out these hard for me to get SH, but sounds like a low charge so far.
    southshorejohn

  5. #5
    Join Date
    Nov 2010
    Location
    N. Idaho
    Posts
    586
    Quote Originally Posted by southshorejohn View Post
    do you have od dry wet temps? With out these hard for me to get SH, but sounds like a low charge so far.
    He noted 95 oat, my TSH doesn't go that hot but i would venture to guess it would be a bit lower than 5 with 63idwb

    He also stated 38sc! Extremely high!
    "I've got my Gas Mechanics license"
    "Yea, well my 16yr old daughter has her drivers license, doesn't mean she knows how to drive"

  6. #6
    Join Date
    Jul 2005
    Location
    Boston/Cape Cod
    Posts
    66
    Quote Originally Posted by Damien View Post
    He noted 95 oat, my TSH doesn't go that hot but i would venture to guess it would be a bit lower than 5 with 63idwb

    He also stated 38sc! Extremely high!
    W/O a little more inform who knows could be overcharge or now that none of the ducts are blocked due to being empty air flow possible
    southshorejohn

  7. #7
    Join Date
    Jul 2005
    Posts
    5,574
    Quote Originally Posted by thecarpenter View Post
    Appreciate some help here , first here is the info, I've been here long enough to know you guys want a lot of data:15 year old , r-22 ,1 1/2 ton rheem split,orfice, low side pressure 68, SH 5.6, T1 46, high side pressure 284, SC 38, T2 88, ambient 95, current draw in range 8.4 amps. Inside at return - dry bulb 77 wet 63, supply - dry 67 wet 53, small 600 sq ft apartment, unit in central hall closet with short supply in furred down ceiling ( 12 unit complex I own , so I have other units to compare data with) PROBLEM - mowing yard and find this unit with suction line ICED up outside -- Been thinking head was a little high in earlier checks ( taken 4 previous readings in 2 prior months, all readings near above), so I cleaned condenser coil --(after cleaning and unit off awhile, I checked line temp 81 against line pressure 147 which made me feel no non condensables in system) when running ,no drop across filter/dryer either. After cleaning, low side barely changed, high side dropped 10 PSI, all else almost same (SC, SH, T1 +T2) - SH says low charge, pressures seem fine- SC says...I don't know :readings taken at valves with my testo 550 . Unit was unoccupied for a week and stat set around 80 when freeze occurred. Any constructive ideas appreciated.
    Thanks
    Greg
    You have a LL or MD restriction. Since the system has been overcharged enough to attain target SH despite the restriction there will be no temperature drop across any restriction in the LL. You still have 20 or more SC at the piston, so no phase change in the LL and no temperature drop.

    Probably the filter-dryer, but to be sure install a line piercing valve on the LL near the piston to measure LL pressure drop. You can take it back off and braze up the hole while you have it pumped down to repair the restriction. If the LL pressure drop is less than 30 psi, then the restriction is going to be in the piston body or in the MD inlet screen (if it has one.)

  8. #8
    Join Date
    Dec 2005
    Posts
    3,987
    The part I dont get is if its 77 in the house and the suction pressure is at 68, how is it freezing, especially when the stat was set at 80? Maybe the blower motor is crapping out intermittantly.

  9. #9
    Join Date
    Apr 2004
    Location
    Des Plaines,IL
    Posts
    1,016
    Quote Originally Posted by thecarpenter View Post
    Appreciate some help here , first here is the info, I've been here long enough to know you guys want a lot of data:15 year old , r-22 ,1 1/2 ton rheem split,orfice, low side pressure 68, SH 5.6, T1 46, high side pressure 284, SC 38, T2 88, ambient 95, current draw in range 8.4 amps. Inside at return - dry bulb 77 wet 63, supply - dry 67 wet 53, small 600 sq ft apartment, unit in central hall closet with short supply in furred down ceiling ( 12 unit complex I own , so I have other units to compare data with) PROBLEM - mowing yard and find this unit with suction line ICED up outside -- Been thinking head was a little high in earlier checks ( taken 4 previous readings in 2 prior months, all readings near above), so I cleaned condenser coil --(after cleaning and unit off awhile, I checked line temp 81 against line pressure 147 which made me feel no non condensables in system) when running ,no drop across filter/dryer either. After cleaning, low side barely changed, high side dropped 10 PSI, all else almost same (SC, SH, T1 +T2) - SH says low charge, pressures seem fine- SC says...I don't know :readings taken at valves with my testo 550 . Unit was unoccupied for a week and stat set around 80 when freeze occurred. Any constructive ideas appreciated.
    Thanks
    Greg
    Air flow may be a bit on the high side. SH is low and SC is too high.
    Is this a matched system?
    Stuart
    Lack of airflow destroys compressors.

  10. #10
    Join Date
    Dec 2011
    Location
    louisiana
    Posts
    58
    Should have stated that when I saw the unit frozen, I cut it off for the day, measurements were all taken next day when I cut unit back on for a while, then cleaned coil. System is not matched, changed compressor 2 months ago, evacuated to 500 mics, new filter dryer (no temp drop across ) Really appreciate all you guys taking time to give ideas! Haven't found the answer yet though. How can SH be low? while SC be so high with given pressures??? With given data, what should SH be ? (outdoor temp and which indoor wet bulb measurement do I use in formula) What do you think about other data I have given, pressures, temps, etc.?
    Thanks again.

  11. #11
    Join Date
    Jul 2011
    Location
    Arkansas
    Posts
    81
    Im with medic, there is a restriction and it has been overcharged to make it work rather than clear the restriction. But I also don't see why it would freeze up under those conditions. So I'm ALSO questioning the blower. Have you checked the capacitor/amp draw? Could be overheating and tripping the thermal saftey. Or an intermittent relay issue.

  12. #12
    Join Date
    Jul 2011
    Location
    Arkansas
    Posts
    81
    Quote Originally Posted by thecarpenter View Post
    Should have stated that when I saw the unit frozen, I cut it off for the day, measurements were all taken next day when I cut unit back on for a while, then cleaned coil. System is not matched, changed compressor 2 months ago, evacuated to 500 mics, new filter dryer (no temp drop across ) Really appreciate all you guys taking time to give ideas! Haven't found the answer yet though. How can SH be low? while SC be so high with given pressures??? With given data, what should SH be ? (outdoor temp and which indoor wet bulb measurement do I use in formula) What do you think about other data I have given, pressures, temps, etc.?
    Thanks again.
    Superheat is indoor return wetbulb/condensor entering air drybulb.

    You said your numbers were taken the day after it froze up. Was it much cooler in the house the day it froze? That little bit of sh could be gone with a cooler house.

    Subcool is so high because there is too much refrigerant in the system and the resfriction is making the refrigerant move slower. Longer times spent chilling in the condensor means cooler liquid leaving the coil which gives you a high subcool. SH is still in range because the extra pressure developed by the over charge is pushing through the restriction and allowing the system to cool. Even though its having to work harder to do so.

  13. #13
    Join Date
    Dec 2011
    Location
    louisiana
    Posts
    58
    Thanks HVAC, am still thinking about all that (not dryer but orfice) and Newold, will check the fan more thoroughly. Great ideas.

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