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Thread: Zero Superheat

  1. #1
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    Zero Superheat

    Recently went on a job and another tech is telling me the condenser coils are dirty because of the high head pressure. Unit was supposedly operating better before they were converted to R22. I feel that the unit is overcharged and flooding the evaporator, and the line is colder at the condenser due to liquid refrigerant boiling off in route back to the condenser. The high head pressure is due to excessive liquid refrigerant backing up in the condenser. I find it hard to believe this condition is caused by a dirty condenser coil. What are your thoughts?

    Fixed metering device
    R407C
    Outdoor ambient 88
    Low side pressure 67.8
    Evap Sat Temp 43.1
    Suction Line Temp 36.7
    Superheat 0 (-6.4)

    High side pressure 232.8
    Condenser Sat Temp 102.1
    Discharge line temp 82.6
    Subcooling 19.5

    Temp split 15
    Discharge air temp 60

  2. #2
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    Agreed but recheck your measurements. You can not have Negative Super Heat!

  3. #3
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    So if im reading correctly the unit was converted to r22 not 407c?

    Sent from my LM-G820 using Tapatalk

  4. #4
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    Thread Starter
    Yes.

  5. #5
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    Correct this is why I am a little puzzled. First time seeing this.

  6. #6
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    So clean both coils, check cfm, recover to correct SH on the chart using indoor wet bulb and outdoor dry bulb.

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  8. #7
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    Well it is hard to believe , but id start by verifying coil cleanliness evap and condenser. Something isn't right. Also the head and suction is similar to 407c and r22 mixed a bit.

    Sent from my LM-G820 using Tapatalk

  9. #8
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    Why was it converted to R22?
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  10. #9
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    A higher head based on a dirty, nasty cond coil causes more freon to go thru the fixed orifice leading to flooding of the comp. Starting from a simple cleaning as suggested sounds like the way to go. Then it would be easier to determine an overcharge.

  11. #10
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    Quote Originally Posted by beenthere View Post
    Why was it converted to R22?
    Sorry it was converted from R22 to R407C.

  12. #11
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    I haven't worked with R407C yet but I don't see a dirty condenser coil with those numbers. It sounds more like a dirty evaporator coil. The head pressure is not high for the outdoor temp & the liquid line is even lower than the outdoor temp so nothing suggests a dirty condenser coil. It could be a dirty evaporator coil & possibly over charged or even a metering device over feeding.
    Gary
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  14. #12
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    19.5 SC kinda means the condenser isn't too dirty. I say pull the evaporator & blower wheel & clean. Go ahead & clean condenser while you have the water hose out.
    Are you sure you don't have your Sat Temp & suction temp backwards & you have 6.4 SH ? Look at the PT chart.

  15. #13
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    Appears to be slightly over charged. Use vendor ssh charging chart, OA DB & RA WB (outside dry bulb & return wet bulb). Condenser approach ~14 df ok.
    Based on 88 oa, ssh could be 10-25 @ 65- 75 wb.

  16. #14
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    Quote Originally Posted by oldguy1949 View Post
    19.5 SC kinda means the condenser isn't too dirty. I say pull the evaporator & blower wheel & clean. Go ahead & clean condenser while you have the water hose out.
    Are you sure you don't have your Sat Temp & suction temp backwards & you have 6.4 SH ? Look at the PT chart.
    Thanks for the advise!! I am fully on board with you this looked crazy to me as well! The smart probes haven't let me down so far. I even put my high side temperature probe on the line to make sure I didn't have a bad sensor. The PT chart for 67 degrees is at 43 degrees saturated. It is a new one for me!

  17. #15
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    The 19.5 SC with only a pressure = to a 12 d rise above ambient just doesn't seem right either. Are you positive it's actually ONE refrigerant, 407C, & not some ahole has mixed 22 & 407 ?
    I ask this cause many years ago I had a R500 unit with really screwy pressures & temps plus they went up & down as you were watching. After at least an hour beating my head against the wall the homeowner finally admitted a guy had been there and added gas but his jug was green & not yellow like mine

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  19. #16
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    Quote Originally Posted by oldguy1949 View Post
    The 19.5 SC with only a pressure = to a 12 d rise above ambient just doesn't seem right either. Are you positive it's actually ONE refrigerant, 407C, & not some ahole has mixed 22 & 407 ?
    I ask this cause many years ago I had a R500 unit with really screwy pressures & temps plus they went up & down as you were watching. After at least an hour beating my head against the wall the homeowner finally admitted a guy had been there and added gas but his jug was green & not yellow like mine
    Not sure, but with pressures like this it will probably be better to recover it all and start fresh!!!

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  21. #17
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    You need to recheck that p/t chart..for the right refrigerant..
    You didn’t list mfg SC either ..
    No mention of txv or fixed..
    RA temp?

  22. #18
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    Quote Originally Posted by Unlimited1 View Post
    You need to recheck that p/t chart..for the right refrigerant..
    You didn’t list mfg SC either ..
    No mention of txv or fixed..
    RA temp?
    Fixed
    Sc 19.5

    Sent from my LM-G820 using Tapatalk

  23. #19
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    R500 a/c unit!!!That goes back a few years.Like 1970.The only unit I ever worked on that took R500,was an old residential carrier.It was a small 3 ton unit.The small little 3 ton unit had a semi -Hermetic compressor in it.I'm getting old too!!!!!

  24. #20
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    I still have 1 yellow cylinder,full.

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