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Thread: high head?..

  1. #14
    Join Date
    Aug 2003
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    Fort Worth, TX
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    11,376
    I have run across them that looked pretty from the outside then I got out the water hose and it looked like a mud slide on the slab.
    I was going to add for mo-flo to check if the coil is a double row job. But then I read about the evap having a cap tube so that made me wonder if the condenser is just as ancient (thereby unlikely to have double coils).

    Last summer I split apart many of the condenser coils at my building. The amount of dirt between the two coil sets was astounding. Just washing the coil from the front or back without splitting it wasn't doing anything for all the crap in the middle.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  2. #15
    Join Date
    Mar 2005
    Location
    Suppy NC
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    4,516
    Originally posted by mrbillpro
    Originally posted by tinknocker service tech
    some of the old cap tube coils ran low back arround 55 to 60.
    This is true! Tin, we are telling our age.
    i was told 32 years ago get out while you can stil do something else heheheh man i should have listened

  3. #16
    Join Date
    Apr 2003
    Location
    the Great Pacific Northwest
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    607
    Condenser motor change. Check the HP rating, speed, and rotation also the fan position in the orfice is very important.
    High head pressure is caused by not rejecting enough (quantity) of heat.
    LL 115d, 78d Ambient, 37d approach too much.
    Kinks would cause low pressures both sides.
    High head pressures:
    Dirty condenser
    Overcharge (look for high subcooling)
    Non condensibles
    Low condenser airflow
    Condenser air recirculation
    High evap air flow and/or humidity causes elevated head
    but not high head normally
    Other causes also but rare.


  4. #17
    Join Date
    Nov 2001
    Location
    east kansas
    Posts
    8,038
    I'm with everyone else, clean the condenser first. Even if it looks clean.

    Can you open the plenum's door and watch the coil. I've ran into some that were not feeding every circuit. Someone overcharged them to get suction pressure up.

    Also, is the CU newer. Maybe the old coil will not work with a higher seer unit.

  5. #18
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    Jan 2004
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    PA
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    68,753
    Originally posted by lynn rodenmayer


    Also, is the CU newer. Maybe the old coil will not work with a higher seer unit.
    Or is the CU a larger tonage then the cap tube indoor.
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  6. #19
    Join Date
    Feb 2004
    Location
    southern illinois
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    the cu is about 15 years old....gonna give him a call and see if he wants me to clean it,but this will be added charge cause that don't come with a furn' changeout...i cleaned the indoor coil for him though,....also he said that the motor was bigger i'm assuming more hp....thanx for replies guys.

  7. #20
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    Feb 2004
    Location
    southern illinois
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    also it is in modular home and the system is mismatched with evaporator made by someone else,...i would have to get file out....will take advice about watching tubes thanx.

  8. #21
    Join Date
    Apr 2003
    Location
    the Great Pacific Northwest
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    Originally posted by beenthere
    Originally posted by lynn rodenmayer


    Also, is the CU newer. Maybe the old coil will not work with a higher seer unit.
    Or is the CU a larger tonage then the cap tube indoor.
    beenthere, et.al
    In the intrest of understanding the refregeration cycle better please explain how a oversized CU would cause high head pressure.

  9. #22
    Join Date
    Dec 2002
    Location
    Houston,Tx.
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    16,121
    [QUOTE]Originally posted by hvac-tech-lane
    In the intrest of understanding the refregeration cycle better please explain how a oversized CU would cause high head pressure.
    I would say probably because of smaller metering device with smaller evap. that will raise the head a tad higher than a normal matched system. Especially on the older cap tube stuff.
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  10. #23
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    Apr 2003
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    [QUOTE]Originally posted by mrbillpro
    Originally posted by hvac-tech-lane
    In the intrest of understanding the refregeration cycle better please explain how a oversized CU would cause high head pressure.
    I would say probably because of smaller metering device with smaller evap. that will raise the head a tad higher than a normal matched system. Especially on the older cap tube stuff.
    How would a smaller metering device raise head pressure?

  11. #24
    Join Date
    Mar 2002
    Location
    Eufaula OK
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    4,175
    I would check the sub cool to see how much liquid is stacking up. If the coil is clean, and fan is working properly that is about all the that can cause hi head. I would guess an under sized orifice or restriction in the liquid line would be the problem.
    That alone does not raise head, but when someone just charges until they get the low up and fill the condenser with liquid, it sure will.
    Jax

  12. #25
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    Jan 2004
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    PA
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    The only way it wouldn't is if it was a txv, sized for the outdoor unit.

    An over sized CU, would have a very low suction pressure at normal head pressures because the cap tube wouldn't have enough flow through it.

    Some one may have miss matched it, and just kept adding gas till they got a decent suction pressure. Which means it has to have a high head pressure to force enough refrigerant through the cap tube to keep from freezing the coil.
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  13. #26
    Join Date
    Apr 2005
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    2
    Replace Consenser Motor, Check for Horsepower and RPM. Make sure it is right rotator (CW/CCW) and suggestion to raise condenser coil with water hose.

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