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Thread: blower speed

  1. #1
    Join Date
    Jun 2005
    Posts
    32
    I am having humidity problems with Carrier 5 ton system. House is 2 years old and 2400 sq ft in size (2 story). My system seems to be short cycling anywhere from 8-10 minutes on time and 8-10 minutes off time (during the heat of the day, which is low 90's here in South Texas). The short cycling gets worse at night (3-5 minutes on 10-15 minutes off). The RH inside the house stays at 60-65% with thermostat set at 76-77 (Honeywell Vision 8320-retail version). I was wondering if I could lower blower speed to lower setting without harming system? I have looked at schematics on blower and it says nothing about CFM only that black wire is "high", blue wire is "med/lo", and red wire is "low". From reading posts I know you are looking for 350-400 CFM for max humidity removal. Does anyone know what the CFM is for each speed on my particular system?

    Carrier PRODUCT #58STA110-10122
    CARRIER MODEL #58STA110-22 (COIL)

    INPUT - 110,000 BTU
    OUTPUT - 89,000 BTU

    ALL THIS WAS TAKEN DIRECTLY OFF LABEL ON UNIT.

    THANK YOU GUYS FOR YOUR HELP!

  2. #2
    Join Date
    Nov 2000
    Location
    Coastal Georgia
    Posts
    34,902
    Yoiu need to solve the short cycle problem and it is not with the blower speed.. 5 tons sounds like a lot. Is the system zoned?

  3. #3
    Join Date
    Jun 2005
    Posts
    32
    Not zoned. Had unit serviced a month ago. Tech told me that unit was slightly overcharged so he removed 1.5 lbs freon. I saw no difference at all as far as humidity removal and the system seemed to struggle with temp on hot days. Called him back out last week and he pumped the freon back in because he did not feel comfortable lowering fan speed. I have closed down all of the registers downstairs to keep cool air off of the thermostat thinking that this is the short cycling problem. But it hasn't helped. I'm stumped!

  4. #4
    Join Date
    Nov 2000
    Location
    Coastal Georgia
    Posts
    34,902
    One T stat two floors. Never good.

  5. #5
    Join Date
    Jun 2005
    Posts
    32
    I know. Anything I can do with humidity removal or extending run times short of spending a fortune on dampers/baffles etc?

  6. #6
    Join Date
    May 2002
    Location
    Colorado
    Posts
    697
    Go ahead and lower the speed a notch and see what happens. Just make sure the evaporator coil doesn't freeze.

    Did the tech leave you with his measurements? If so, what were they?

  7. #7
    Join Date
    Jun 2005
    Posts
    32
    First visit readings were:

    Head pressure- 195
    Suction- 65
    Delta- 18 degrees
    Superheat- 17 degrees
    Subcool- 13 degrees

    On second visit he did not document pressures but i did watch him while he was recharging unit and from what i remember the readings on his gauges were 225/45 and the superheat was 1-2 degrees (temp outside was 93 degrees).

    He also noted that compressor was operating at max rating of 18.7 amps (actual reading was 18.4)

  8. #8
    Join Date
    Nov 2000
    Location
    Coastal Georgia
    Posts
    34,902
    45? can't be right.

  9. #9
    Join Date
    Jun 2005
    Posts
    32
    I'm probably giving you an incorrect suction number. I'm pretty sure about the head pressure reading. The reference chart on the condenser called for a 6 degree superheat. He was able to get a 1-2 degree superheat that day. He told me that it would level off in a couple of days but the superheat would be lower with slight overcharge. Sound right? I'm a complete novice when it comes to these things it just seems that unit cannot pull humidity out of house running just 8 minutes at a time.

  10. #10
    Join Date
    May 2002
    Location
    Colorado
    Posts
    697
    If I were you I'd get a TXV put on your system. Then you can screw around with blower speeds and get thing just right.

  11. #11
    Join Date
    Jun 2005
    Posts
    32
    Anyone know what the CFM is on med and low fan setting. Schematics on unit don't say what actual CFM is, just high, med, low

  12. #12
    Join Date
    Nov 2000
    Location
    Coastal Georgia
    Posts
    34,902
    I would see if you can get a additional thermostat and zone the system.

  13. #13
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,470
    Make sure the fan is "auto" setting. Widen the deadband of the t-stat to 3^F. The temp in/out should be 20-25^F difference. Next consider adding dehumidification for the evenings and rainy weather humidity control.

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