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  1. #1
    Join Date
    May 2010
    Location
    Northern Virginia
    Posts
    18

    Penn water valve? plugged coax coil? or both?

    I have a 5ton server room AC with glycol drycooler that has been cutting out on high head pressure; If I open the Penn valve wide open & run the drycooler pump continuously the ac works fine. When running like this the head pressure is about 150 psi (R-22). It has a tube in tube coax condenser coil which measures a TD of just 3-5 degrees between inlet & outlet water temp (is it plugged-up?). If I try adjusting the head pressure control for higher opening pressure I get no change until near the end of travel. Then my head pressure rockets up toward cut-out (375psi), the coil temperature also rockets up & it trips out before I can back it off ( faulty water valve?). So... Faulty valve? Plugged coil? Both? Any advice?
    Last edited by whoaghi; 05-15-2010 at 08:00 AM. Reason: this is commercial equipment

  2. #2
    Join Date
    Jun 2004
    Location
    Howell, Michigan
    Posts
    16,168
    Moved to Commercial HVAC.

  3. #3
    Join Date
    Jan 2007
    Location
    Milwaukee Wisconsin
    Posts
    984
    Just a gut feeling - Delta T leads me to believe fouled coil. How old is the system and condition of the glycol? I've seen it "gel up" and stick to the surface. If this is a critical situation (no back-up equip.), maybe replacing both - costly but customers don't want us back. (If you have valves - yeah right!). Please keep us posted.
    Last edited by HVAC Teacher; 05-15-2010 at 10:02 AM.

  4. #4
    Join Date
    Jun 2008
    Location
    Apopka, Florida
    Posts
    110
    Agreed, you should have a higher TD across the coaxial condenser. Keep us posted on the resolution.

  5. #5
    Join Date
    Jan 2008
    Location
    Dallas ,Texas
    Posts
    3,700
    I'm just not sold yet that it's a fouled HX with the 150psi head pressure. What is the average temp of the condenser water? Describe the set-up more, water pump , Penn valve. What's the actual EWT and LWT during both conditions ?
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

  6. #6
    Join Date
    Jul 2009
    Location
    In a mechanical room....
    Posts
    1,887
    Whats the approach on the heat exchanger? That will confirm it being fouled.
    “It takes courage to grow up and turn out to be who you really are.”

    - E.E. Cummings

  7. #7
    Join Date
    Jun 2005
    Location
    Portland Oregon
    Posts
    87
    I would think that if your condenser was fouled you wouldn't get any head pressure change when you back the valve off. Sounds to me that the bellows maybe be gone. If this is a Liebert then there is a schraeder core where the bellows gets its pressure. The do make a bellows rebuild kit you can get at your local whole saler or at your Liebert dealer (if it is one) also don't forget to shut your water off. If you want to be safe get the whole valve, just in case the pin that drives the valve got bent from when you were running it in and out
    do things right the first time is cheaper.

  8. #8
    Join Date
    Apr 2006
    Location
    mechanical room
    Posts
    1,255
    sounds like a bad valve, but if it's a critical unit like said have that condenser in the truck just in case, but if we can get some info. on setup and temp./press. readings, was workin on a pool dehumidifer last week that tripped out hi press., arrived and found the remote air condenser running, bumped up the pool water temp. setpoint up and bamm locked out on hi press., i piped in some gauges across the water condenser and found the delta p 4 times higher than it shoulda been

  9. #9
    Join Date
    May 2010
    Location
    New Hampshire
    Posts
    3
    The approach measure is right on for fouling. You could have a combination of issues. Could be very cold water supply and or valve water supply over pressure. Just a guess. I think the Penn valves can close off at up to a 75 PSID, could be 50 PSID though. I say this because a system could exhibit low charge symptoms if over cooled by the extra water flow. This could lead to an overcharge if missed. Then the two issues would counteract each other, and leave you with low capacity and high head during high load or when the water pressure changed.

    All water cooled refrigeration does is dump energy into the condenser water, heating it to within a couple degrees of the saturation temperature in a normal situation with plenty of water capacity. Unfortunately the delta T only measures part of the problem. You can have a 3 degree TD at high flow that could equal the same energy rejection as a 20 degree TD at lower flow. The consolidated relationship for energy movement in water is “TD in F” X “GPM” X “500.4” = BTUs/hr. Throw in the Specific Heat factor for glycol mix. Without the GPM the TD tends to be a subjective measure.

    Best of luck to you.

  10. #10
    Join Date
    Jan 2007
    Location
    Milwaukee Wisconsin
    Posts
    984
    Good point! Check the approach!

    Careful! Not all have schraeder cores!

  11. #11
    Join Date
    May 2010
    Location
    Northern Virginia
    Posts
    18

    thanks for input, and questions; here's more

    The water pump is new; Recent notes show EWT-66 deg / LWT-71 deg. with a pressure of 173/50 psi; That gives me an approach temp of 20 deg.
    (shouldn't it be closer to 10 deg?) Temperatures measured: Liq.line 82 deg & suc.line 49 deg; thats 11 deg sub.cool & 23 deg sup.heat; TD across the evap coil was 19 deg. & cooling good; Until it reaches set point, then the HX coil stays so hot that on restart head press. soars till it trips. Initially I tried a true-off delay timer to keep pump running 10 min. to help remove heat from HX. (not enough); Only by setting for 20 min. with Penn valve wide open will it run.

  12. #12
    Join Date
    Oct 2001
    Posts
    6,942
    internal condenser tubes are fouled up back clean with a light acid teel pump and a 5 gallon bucket.
    "when in doubt...jump it out" http://www.youtube.com/watch?v=U1qEZHhJubY

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