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  1. #1

    AC blowing cold but not cooling house

    Unit: 3 ton Carrier (AC only)
    Home: 1400 sq/ft
    Cooling area: 940 sq/ft

    I bought my house September last year and have not needed to turn on my AC until now. I noticed that it runs for a very long time when attempting to cool the house. Yesterday it was 90F outside so I turned my AC on when I returned from work at 3:30p at which time it was 80F in the house. At 8:00p the unit had not cut off and only cooled the house 3F, making it 77F inside. I checked the air temperature at all registers and it was 43F. Air temp at return was 67F. The seller of the home advertised "New duct work." A lot of things around the house seem like they were done by non-professionals, including the duct work. There are 10 registers throughout the house, all with 6" duct. My cousin is HVAC certified and seems to think that I need to add 6 more registers throughout the house to solve the problem. The vents seem to be blowing really cold air with not much force. I'd like a second opinion before I go cutting more holes in my floor.

    Today is 86F outside. With the thermostat set to 74, it takes an hour of running time to cut itself off. I'm afraid of my power bill being too high, especially in the middle of summer.

  2. #2
    Join Date
    May 2008
    Location
    Central Fla.
    Posts
    311
    you need to have a manual J and a manual D run on your home to see if it is sized right and it will also give you a duct design(not really but it will tell you what you need for each room). Sounds like you need a Pro out there to steer you straight.

  3. #3
    Join Date
    Jul 2002
    Location
    SE Texas
    Posts
    436
    It was 77 inside and 67 at the return? That's odd.

    The air coming out of the registers was 43? What's your filter look like. What's the evaporator coil look like? What's the blower wheel look like?

    Did you have the home inspected before you bought it? Did you have the A/C system inspected before you bought it?
    With your chrome heart shining in the sun, long may you run.

  4. #4
    Been a while since my last post...

    SandShark: Changed filter 2 weeks ago. Coil looks fine, slight frost on the line but not enough to cause my problem. My HVAC certified cousin said the blower wheel is fine. I did have the home inspected before I bought and the inspector crawled around under the house with me to check duct work and such. Did NOT have AC inspected before buying (oops).

    I have a bit more information since my last post. I'm still having the same problems. Today is 87F outside, inside home 73. AC runs for hours, cuts off for 10 min, then clicks back on. Seems to be struggling to cool house.

    I ran a (silly-to-professionals) test on each register because it seems that the temperature coming out is good, but amount of force behind it is low. I have floor registers so to test the amount of air coming out, I placed printer paper over each one individually and counted how much paper each one could hold without blowing it off. I know this is probably a dumb test, but it does tell me which registers are blowing stronger than others. All but one register held 8 pieces of standard printer paper without moving them. The strongest register held 12, 1.5x stronger than the others. Crawling under the house today, the strongest one is first on the line of duct work as I suspected. The flex under the house is pinched in a lot of places at points where it is held to the floor joists by mesh and/or duct tape. At some of these pinch points, the flex is half its normal diameter. I checked for major leaks and found none.

    Could the pinched flex be my problem? Anyone bored enough to try the printer paper test and let me know how much your registers could hold?

  5. #5
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,060
    Quote Originally Posted by dlovelace024 View Post
    Unit: 3 ton Carrier (AC only)
    Home: 1400 sq/ft
    Cooling area: 940 sq/ft

    I bought my house September last year and have not needed to turn on my AC until now. I noticed that it runs for a very long time when attempting to cool the house. Yesterday it was 90F outside so I turned my AC on when I returned from work at 3:30p at which time it was 80F in the house. At 8:00p the unit had not cut off and only cooled the house 3F, making it 77F inside. I checked the air temperature at all registers and it was 43F. Air temp at return was 67F. The seller of the home advertised "New duct work." A lot of things around the house seem like they were done by non-professionals, including the duct work. There are 10 registers throughout the house, all with 6" duct. My cousin is HVAC certified and seems to think that I need to add 6 more registers throughout the house to solve the problem. The vents seem to be blowing really cold air with not much force. I'd like a second opinion before I go cutting more holes in my floor.

    Today is 86F outside. With the thermostat set to 74, it takes an hour of running time to cut itself off. I'm afraid of my power bill being too high, especially in the middle of summer.
    start with unit over sized and low airflow.

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