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  1. #1
    Join Date
    Jun 2011
    Posts
    4

    Default air flow problems

    I am having an air flow problem after my central a/c runs for 2 or 3 days, I notice that the air flow coming out of the vents starts to decrease. I have changed the filters, the evaporator is clean and dont appears to be icing over, its a one speed blower motor, the only I see is that the ducts have a lot of condensation dripping of the ducts. Any Ideas?
    Thanks

  2. #2
    Join Date
    Jul 2010
    Location
    SoCal
    Posts
    5,081

    Default Re: air flow problems

    You seem to have more than one problem here.

    How old is your cooling system? What kind of ducts do you have? galv sheet metal, I bet. Are they dirty inside? Get up into the attic early in the morning and check your ducting system, connections, tape around them, hangers - a complete check up. See if any air is escaping out from the ducts.

    The drip is probably caused by higher than normal temperatures and humidity levels this year. Start running your a/c early, before it gets very hot or too humid and set your desired temp at 79-80, not the low to mid 70's.

    If you have metal ducts, consider replacing them with new insulated flex ducts.

    Also, have an a/c tech perform a complete tune up, to include checking the coil compartment. Clean the pyramid, if necessary.

    The sooner you tend to your problems, the better.

  3. #3
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,381

    Default Re: air flow problems

    Condensation in the ducts means you have a major problem, but one that is probably easily fixed and not very expensive either.

    First thing to check is the drain underneath the evaporator coils. If the tray under the evaporator coils is filling up with water, then you need to have the drain line blown out.

    The other source of condensation would be from warm moist air entering your ducts after the evaporator. Now I know the ducts have positive air pressure so any leaks should be from the inside of the duct out, not drawing air in, but you might have a leak that is acting like a venturi. The principle here is MMF or motomotive force. If the breach in the duct points backward from the direction of the airflow, then the airflow will create a vacuum in the breach and draw air in. To fix this would be to find the breach and seal it, or just seal all the joints in the ductwork.

    BTW, I think you do have a little icing of the coils, just not that bad yet.

  4. #4
    Join Date
    Jul 2009
    Location
    Northeast
    Posts
    661

    Default Re: air flow problems

    Sounds like your ductwork needs to be insulated, as for changing to flexduct I wouldn't as you'll lose more air, unless you go to the next size up. Nothing is better that metal for ductwork, flex is just quicker to install and cheaper.

  5. #5
    Join Date
    Jun 2011
    Posts
    4

    Default Re: air flow problems

    UPDATE
    The ducts have been sealed, the drain pipe has been blown out, the system is 8 years old and in the basement that is a walkout basement, and it has metal ducts that I cleaned last summer because of the same problem. Had two A/C companies in to look at it last summer and neither one found anything wrong.

  6. #6
    Join Date
    Feb 2012
    Location
    Minnesota
    Posts
    3

    Default Re: air flow problems

    Rather than create a new thread, I thought I might piggy back on this one, as I'm having one issue that's similar.

    I'm not having the condensation issues whatsoever, thankfully, but am having some issues with uneven cooling/heating on the second floor.

    Not too long ago, I had someone come out to repair the outdoor AC unit as it was no longer producing cold air. Fortunately it was a quick replacement of the capacitor in the unit.

    During the service call, the HVAC repairman found some partially closed dampers and went through and opened them. This certainly increased the air flow through the registers, but I'm still having issues cooling the second floor.

    I'm considering trying to close off (not completely) the duct work to the first floor, but am not entirely sure which ducts go where. I'm fairly confident of which one feeds the second floor, as one of the paths goes up the middle of the house rather.

    The remaining duct work goes to the outer wall of the house in two cases and into the middle in one case - all of which go directly up to where a vent is on the first floor.

    My plan is to close the dampers to those ducts to see if it helps the output on the second floor, then partially re-open each of the others. Does this make sense as an attempt to rebalance, or am I taking a big risk with this plan?

    Thanks!

  7. #7
    Join Date
    Apr 2012
    Location
    Northern Virginia
    Posts
    140

    Default Re: air flow problems

    Quote Originally Posted by NewOwnerMN View Post
    Rather than create a new thread, I thought I might piggy back on this one, as I'm having one issue that's similar.

    During the service call, the HVAC repairman found some partially closed dampers and went through and opened them. This certainly increased the air flow through the registers, but I'm still having issues cooling the second floor.

    I'm considering trying to close off (not completely) the duct work to the first floor, but am not entirely sure which ducts go where. I'm fairly confident of which one feeds the second floor, as one of the paths goes up the middle of the house rather.

    My plan is to close the dampers to those ducts to see if it helps the output on the second floor, then partially re-open each of the others. Does this make sense as an attempt to rebalance, or am I taking a big risk with this plan?

    Thanks!
    I'm not technical on HVAC, but sympathize with your problem as I also have a tempertaure imbalance between the 1st & 2nd floor from the 1-zone system. It's been 2 weeks and no additional postings, so I'll jump in.

    First, I didn't understand what you are saying about "closing off the duct work" to the 1st floor. If you can do that, then your probelm is solved. I heard of systems where there is a motorized damper in the ductwork that can close off air flow to one section or another. This is different than closing/opening the louvers in the air registers which every register can do (if it's not stuck).

    I don't have any duct dampers or diverters, motorized or manual (that I can find in my 1964 house). I have registers with louvers that can open/close.

    My 2nd floor is significantly hotter than the 1st (about 75 on 1st, 82 on 2nd floor, when outside is 95+ and A/C running 18-20 hours/day). My house is also a cape cod style, which means the 2nd floor is the attic and proper insulation seems more critical than if the attic is above the 2nd floor. Whether more or proper insulation would help was beyond my timeframe and affordability.

    As you said, I also tried 7/8 closing off the 1st floor air registers, thinking more air would flow to the 2nd floor based on my hypothesis that pressurized air would flow to less constricted openings in the 2nd floor. I don't know about the science, but I didn't feel (by hand) any more air flow or therometer (maybe 1 degree better ?). However, a poster on this site recommend AGAINST closing off a large number of registers - - I don't know his technical thinking, but he warned of stressing the blower and refrigerant system.

    I did two more things that applied to my situation, that seemed to help alot.

    One was to close the doors of the 2nd door rooms; basically, the 2nd floor air return was drawsing cooled air from the rooms. You can feel the positive pressure from the air return when you shut a door -- the pressure forces a door to move to a more closed position. However (there's always a however), another poster said cooling is caused by hot air drawn out and cooled air taking its place. When you close the room doors, the warm air in the rooms is not drawn out even if the cooled air stays in the rooms. In any event, the rooms FEEL cooler from trapping both warm air and cooled air from the air registers.

    More recently, I began using a CHEAPER, less dense air filter that apparently allows more air (and more pollution) to pass from the returns. My previous filter was MERV 13; I went to a MERV (either a 6 or 8); don't use the $1 fiberglass as it will pass a lot of crap to the coils. My strategy is to use a MERV 13 filter to June, then a MERV 8 during the hottest 3 months, and replace it with a 13 filter until the next year (I have a packet of MERV 13 so want to use them and keep the ducts/coils as clean as possible). The side effect is that BOTH the 1st & 2nd floors have (marginally) more air flow, but overall, the 2nd floor ROOMS feel better balanced to the 1st floor. The constant opening & closing of doors on the 2nd floor is a nuisance, though.

    That's my long story.

  8. #8
    Join Date
    Jan 2008
    Location
    Texas
    Posts
    128

    Default Re: air flow problems

    Since you are experimenting, don't make alterations until you know the effect. Use pieces of cardboard or duct tape on the back of vents to close them off for now.

    Hot second floors are common, heat rises. Best if A/C can be made to draw from up there. I have even seen one house where a recirulating fan/duct was built into a closet that pushed air from below. Suggest checking insulation and window types on second floor, close blinds or heavy curtains, maybe even reflective film on windows.

  9. #9
    Join Date
    Jul 2012
    Location
    Manhattan
    Posts
    17

    Default Re: air flow problems

    A huge reason for inflated heating and cooling bills can be attributed to airflow problems within the HVAC system. There are many possible causes, and each result is the same: little or no airflow out of your supply air registers. Determining the cause is relatively easy if you know where to look.

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