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  1. #1
    Join Date
    Jun 2005
    Posts
    37

    Frown

    My house is a year old. The AC will not get the house below 80 in the middle of the day. With it being 95 degree's with a 53 % humidity outside.

    Yesterday a tech came out and did some air balancing and checked the freon charge. It is still under warranty. Before the tech came out the house wouldn't cool bellow 82 degree's. The tech told me that the system was overcharged by 1 lb. I looked on the unit and it say's factory charge is 6.2 lbs. The tech said he removed 1 lb from the system. He seemed nice and helped explain alot of stuff. The temp on the line before he removed freon was 44 degree's. When he left I believe it was 61 or 62 degree's. He said the ideal is 60 degree's.

    I recorded the temp today and at 3:22 it was 80 on the thermostat. It is 5:42 and it is still 80.

    I have a carrier a/c model #38BRC030-321 SERIAL 0904E21623

    The tech's diagnostics
    S/A 57
    R/A 77
    SUCTION 73
    HEAD 220
    ODT 95
    T-SAT SETTING 76

    The home I live in is a Perry Home and is 1733 s.q. ft.
    I know our a/c shouldn't have to run all day and not cool the house right. Plz help

  2. #2
    Join Date
    Jun 2005
    Posts
    37
    return air temp is 77 degree's

    Air at the vents to room is 64 degree's

  3. #3
    Join Date
    Jun 2005
    Location
    New York
    Posts
    207
    I hope that the 030 in that model number doesnt mean 2 1/2 ton. looks like that machine is working. If its a 2 1/2 ton, its too small. Would like a liquid line temp reading

    [Edited by ultratec on 06-22-2005 at 07:05 PM]

  4. #4
    Join Date
    Jun 2005
    Location
    New York
    Posts
    207
    You have a 7 deg. temp lose in the ducts, are they in a very hot attic and are they insulated? Hope its not a 2 1/2 ton..

  5. #5
    Join Date
    Apr 2004
    Posts
    7,680
    Yes I would want to know why your supply air is gaining so much from the outlet of the coil to the supply airregister also. That is a significant loss of capacity. The other numbers also agree with a high load or possible undersized unit but I wouldnt jump to that (undersized) conclusion until you find the reason for the duct losses. It may just do the job if you had 58-59 degree air going to the room.

    It seems your ducts must run in the attic. Maybe your attic isnt ventilated well or the insulation is less than desireable for the ducts. Better have a look at that.

  6. #6
    Join Date
    Jun 2005
    Posts
    37
    The ducts are in the attic. The tech is coming tommorro again is there any questions I should ask. The reading on the vent which is farthest away from the unit (I looked at the duct in the attic to tell this) read 64. The reading closest to the unit is 62 degree's. The return air reading is

    What is the ideal temperature to have in the attic on a 95 degree day? What should the unit be able to bring the house down too? I believe the tech told me that this unit was 2.5 ton's. He said Perry Homes sizes there unit's at the lowest possible. Is there any recourse I should try to have with Perry Homes? In the attic there are two square vents at the highest point. They are not powered and have no fins on them.

    This is pretty crapy having a new house that won't get bellow 80 degree's in the summer time.

  7. #7
    Join Date
    Aug 2003
    Posts
    626
    Do you have a return that goes into the attic? If so check for duct leakage. should also check supplies and air handler for leaks.

  8. #8
    Join Date
    Jun 2005
    Posts
    37
    Yes the return goes in the attic? I checked the duct for leakage, the supply lines, and the air handler. I felt a tiny bit of air movement where the return air goes into the a/c not much barely enough to feel. On the air handler there are a couple of small leaks like were some screw holes are and such. I have to say the job they did with the mastic on the duct is quit crapy. You can see black cracks where they didn't get a good seal.

    Any suggestions on what I should have the tech do tommorro?

  9. #9
    Join Date
    Jun 2005
    Posts
    37
    What should the ideal temp difference be b/t the air entering the return air at the grill and the air exiting in a room at a vent?

  10. #10
    Join Date
    Nov 2003
    Location
    northern mass
    Posts
    411
    Sounds to me like your duct insulation is too low ( r-factor), and is not sealed properly. Your unit paperwork should show what the plunem rise is (difference between the return air and supply air measured in plunems).

    That is where I would start. Next have the tech check the actual sizing of the duct work and the amount and placement of returns. Looking at T-stat placement is also a good idea.

    Also, depending on things like geographical location and house specs it's hard to say, but it sounds like your system is undersized by about a ton or so.

  11. #11
    Join Date
    Jun 2005
    Posts
    37
    Since this is a Perry Home and the home buyer doesn't have a choice on what size ac there should be what would you recommend if the system's is too small?

    From everyone's post I have gathered the following:
    1.) System may not be large enough

    2.) R-factor of duct may not be high enough (tonight when the attic cool's I will take readings at the vents again)

    These are my main concern's:
    1.) Why was the system overcharged by 1 lb and after it was corrected did it not make that much difference in preformance?

    2.) Why is there a 2 degree difference in temp from vent closest to unit to vent farthest?

    3.) It seem's if the return air is sucking hot air at the plenum that the total house cooling would be affected but it doesn't seem to have those "huge" airflow leaks?

    4.) How much does attic ventilation and temperature play on cooling?

    5.) What would you expect the normal reading to be at the vents in temp?

  12. #12
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,438

    Cooling Capacity VS. 1733 SF Required

    Originally posted by smp7015
    this is a Perry Home From everyone's post I have gathered the following:
    1.) System may not be large enough
    2.) R-factor of duct may not be high enough

    These are my main concern's:

    5. What would you expect the normal reading to be at the vents in temp?
    Diffuser air temperature should be < 60'F under the stated conditions .. RA = 77'F.

    IF diffuser outlet is > 60'F with 57'F SA, you may wish to investigate whether duct is R-6. Replacing some of the duct with R-8 and tinting some selected windows may improve the performance of the existing equipment.

    .......
    Do you have a lot of windows? ( > 320 S.F.)

    Is there any tinting on the glass?

    ........
    A/C seems to be only Marginally Undersized.
    You may anticipate that the A/C may run for 6+ Hours Straight if it's 95'F outside and t-stat setpoint is 75'.

    Best of luck.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  13. #13
    Join Date
    May 2003
    Location
    Sarasota. Fl
    Posts
    1,301
    You need to have them take the supply and return temps at the unit.

    Then have them take the temps at the registers.

    If your return air is 77 at the grill ....but 84 at the unit, you have found the problem.

    Are your neighbors having the same problems?

    If not its probably not a sizing issue.(assuming similar homes)

    I suspect your gaining heat in the duct work.....either on the supply or return side.

    Good luck and remember to let us know what happens.

    It is the job of thinking people not to be on the side of the executioners.

    ~Albert Camus

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