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  1. #1
    Join Date
    May 2008
    Posts
    12

    Restriction and no superheat?

    R22/10 ton A/C Split... Suction pressure 30psi, suction line temp 16 Deg. Unit looked to be flooding back, i had no super heat out of the evaporator. Air flow is correct. I know that because circuit 2 runs perfect the evaporator coil is all interlaced w/circuit 1. Knowing all this information i elected to replace the txv after making adjustments to the original had no effect. The new TXV failed to correct the problem. ...we did finally find it had 3 of 4 distributor tubes plugged w/silver solder from the factory. How or why would a restriction look this way?

  2. #2
    Join Date
    Apr 2007
    Location
    Philadelphia
    Posts
    2,192
    Quote Originally Posted by hvac689 View Post
    R22/10 ton A/C Split... Suction pressure 30psi, suction line temp 16 Deg. Unit looked to be flooding back, i had no super heat out of the evaporator. Air flow is correct. I know that because circuit 2 runs perfect the evaporator coil is all interlaced w/circuit 1. Knowing all this information i elected to replace the txv after making adjustments to the original had no effect. The new TXV failed to correct the problem. ...we did finally find it had 3 of 4 distributor tubes plugged w/silver solder from the factory. How or why would a restriction look this way?
    Your "starving" your evaporator. So your back pressure would be low. You cannot pick up much heat when you have restricted flow through the evap. What was the head pressure?

  3. #3
    Join Date
    May 2008
    Posts
    12
    Head pressure = 275psi unit had fan cycling

  4. #4
    Join Date
    Apr 2007
    Location
    Philadelphia
    Posts
    2,192
    Quote Originally Posted by hvac689 View Post
    Head pressure = 275psi unit had fan cycling
    Its always good to jump out the fan cycle control when trying to diagnose a system.

  5. #5
    Join Date
    May 2008
    Posts
    12

    Smile

    yep.. i understand having low back,pressure, i just cant understand why the unit was flooding back to the compressor.

  6. #6
    Join Date
    May 2008
    Posts
    12
    Thank you, that is a grate pointer! i wonder if i had done that would i have had the high super heat... then pointing to a restriction

  7. #7
    Join Date
    Apr 2007
    Location
    Philadelphia
    Posts
    2,192
    Quote Originally Posted by hvac689 View Post
    yep.. i understand having low back,pressure, i just cant understand why the unit was flooding back to the compressor.
    You say its flooding back due to the fact that you had no superheat? If you understand as you say then you know with that big of a pressure drop due to the restriction and a low pressure in the evap your not absorbing any heat to "superheat" your refrigerant. when your not evaporating you prolly not condensing either, Which is why i asked for the head pressure and which is why it is good practice to jump that out and see whats going on.
    The metering device is already the biggest pressure drop in a system, So the clogged up distributors will make this even worse

  8. #8
    Join Date
    Apr 2008
    Location
    On the roof
    Posts
    136
    Couple of small questions. Did you replace the filter drier? What brand and age is this unit? How long is the run?
    If you didn't do it right the first time it probably makes sense that your here asking the right way to do it now

  9. #9
    Join Date
    May 2008
    Posts
    12
    Couple of small questions. Did you replace the filter drier? What brand and age is this unit? How long is the run?

    drier replaced yes. unit is on it second season. its a custom unit i cant remember the design company the compressor is feet from the evap and the condenser is remoted 15 ft away. it also uses hot gas. we found the distributor plugged.

  10. #10
    Join Date
    Apr 2007
    Location
    Philadelphia
    Posts
    2,192
    Quote Originally Posted by hvac689 View Post
    Couple of small questions. Did you replace the filter drier? What brand and age is this unit? How long is the run?

    drier replaced yes. unit is on it second season. its a custom unit i cant remember the design company the compressor is feet from the evap and the condenser is remoted 15 ft away. it also uses hot gas. we found the distributor plugged.
    Was the hot gas not feeding the entire time if you where running 30 back pressure?
    Did you remember if you were feeding before or after the evap?

  11. #11
    Join Date
    May 2008
    Posts
    12
    Was the hot gas not feeding the entire time if you where running 30 back pressure?
    Did you remember if you were feeding before or after the evap

    Hot gas entered the evaporator at the distributor. We valved off hot gas.

    head pressure 275psi
    suction pressure 30psi
    suction line temp 16 degrees Fahrenheit

    looked like flooding to me, i did not bypass head pressure control it has a 70 pound receiver and was 1/2 full. we found 3 of the 4 distributors plugged

  12. #12
    Join Date
    May 2008
    Location
    Southern California
    Posts
    55
    Seems to me that if you had 75% of the evaporator shut down from the solder that the other 25% would have trouble absorbing the heat required to boil even the least amount of refrigerant going through the TXV.

    MIke

  13. #13
    Join Date
    Dec 2005
    Posts
    1,905
    Quote Originally Posted by hvac689 View Post
    R22/10 ton A/C Split... Suction pressure 30psi, suction line temp 16 Deg. Unit looked to be flooding back, i had no super heat out of the evaporator. Air flow is correct. I know that because circuit 2 runs perfect the evaporator coil is all interlaced w/circuit 1. Knowing all this information i elected to replace the txv after making adjustments to the original had no effect. The new TXV failed to correct the problem. ...we did finally find it had 3 of 4 distributor tubes plugged w/silver solder from the factory. How or why would a restriction look this way?
    10 ton system with 4 distribitor tubes - I find it is odd ? Did not say it is wrong

    Circuit #1 and #2 -- are they tied together as one common suction line out of the coil ?

    30 PSIG and 16 degree suction line temp -- that gives you 9 degrees super heat and not at NO SUPER HEAT

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