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  1. #1
    Join Date
    Jun 2005
    Posts
    14
    I recently installed a 2 1/2 ton Goodman CLQ condenser with the manufactures performance rated 5 ton TXV coil on a 2 stage variable speed furnace. The HVAC-Calc shows a heat load of 28,251 BTUH. The system charge is producing a subcool of 15F at 210 psi. Superheat is only about 9F at the condenser. CFM over the coil is 990. The problem is that the unit runs continuously and still can't get the indoor temp below 73F. The air flow is very limited with insufficient cooling to the second floor bedrooms even after adjusting the duct dampers. I have not installed many TXV systems. Do I need to worry about the superheat being so low? Could the system be overcharged? Once the charge is set, can the CFM be increased to provide additional air flow to a second story? What will that do to the subcooling and superheat numbers? Will the TXV compensate for the increased air flow or will it need to be adjusted? Will that have an adverse affect on efficiency? Any other ideas on how to increase comfort and cooling?

  2. #2
    Join Date
    May 2004
    Posts
    53
    2.5 ton condenser with a 5 ton coil? Who matched that up?
    Coil size should be within one ton of condenser. Preferably smaller.
    More than likely your coil is too warm. Should have about a 15-20 degree drop with a txv. I would rather see a 2.5 ton coil with a 3 ton condenser.


  3. #3
    Join Date
    Jun 2005
    Posts
    14
    This is a match recommended and rated by Goodman.

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,765
    9° super sounds like the txv is over feeding.
    Could be over charged.

    15 subcool is more then most units require.

    Charge should have been weighed in, and then double checked.

    210 psi head, deosn't tell much, with out the conditions at that time.

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  5. #5
    Join Date
    Jun 2005
    Posts
    14
    I initially weighed in the charge based on the Goodman table for oz/ft of line set minus the 15 feet of pre-charge. After allowing the system to run for 30 minutes, on a 75 F day, we got a reading of 160 lb pressure on the liguid line and 85 F for 2 subcooling. The suction line was 80 lb and 47 F for superheat of 1. I then added charge while watching the subcooling. This brought me to the current situation. Does the TXV need to be adjusted on the 5 ton coil to compensate for the 2 1/2 condenser. If so how should it be adjusted? With TXV is it safer to be slightly under rather than over charged?

  6. #6
    Join Date
    Jun 2003
    Location
    Florida
    Posts
    9,548
    From what you posted, I'd be looking at that coil size and airflow issues. With your 9 degrees of superheat, you're fine. The compressor isn't slugging liquid. With the 15 degrees of subcooling, you're also fine. Liquid isn't stacked up in condenser. So why isn't it cooling? I'd check the delta t, and look to increase the airflow. I agree with the coil looking suspicious....even though you say it's a match. Also check the static pressure....poor duct design perhaps?
    If everything was always done "by the book"....the book would never change.

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,765
    Is the txv factory, or feild installed.
    Is it sized for the outdoor unit, or theindoor.
    Should be sized for the outdoor.
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  8. #8
    Join Date
    Jun 2000
    Location
    NC
    Posts
    108
    Did you do a load calc on the building? Sounds like the equipment is under sized. Is the fan settings correct?

  9. #9
    Join Date
    Jun 2005
    Posts
    14
    The TXV is factory installed and as far as I can tell was not necessarily sized or adjusted for the condenser. There is an adjustment but I'm not sure what I should be looking for when I change it. I checked with Roboteq and he said the TXV should be fine for the 2 1/2 ton unit.

    Lifer,
    HVAC-Calc shows a heat load of 28,521 BTUH. Spec calls for 1000 CFM but at that I could not get enough cooling to 2nd floor. Currently it's set to 1210 CFM.

    Should I try adjusting the TXV? How?

  10. #10
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,765
    Without a pt infront of me, 210 head just sounds too high for a 75° outdoor temp.

    Sounds over charged.

    Robo should know if that txv can work with a 2.5 ton condenser, but I would think it would have trouble throttling down low enough, without adjustment. JMO.

    As a test, I would recover the extra gas put in. And then adjust the txv in till I got a 12° super heat at the bulb location, or just outside the case. And then recheck my sub cool, and coil delta. This should be done with the cfm set to 1000.

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  11. #11
    Join Date
    Apr 2004
    Posts
    7,680
    Your problem has nothing to do with the TXV.

    Your problem is you have a load issue.

  12. #12
    Join Date
    Jun 2005
    Location
    Crisfield, Maryland
    Posts
    20
    Your coil should be smaller. % ton is not efficient with 2 1/2 condenser.Also might look into zone damper to regulate mor air upstairs when downstairs is satisfied. More fan speed would also help some, but with proper charge and evaporator coil temperature you should not have problem.

  13. #13
    Join Date
    Jun 2005
    Posts
    14
    Interesting that you say that this coil/condenser combo is not efficient since the condenser is 14 SEER but with this coil is actually rated at 15 SEER.

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