A/C not cooling during the day
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  1. #1
    Join Date
    Jul 2005
    Posts
    40
    I've seen this topic a few times on this forum but due to hijacked threads I'm not sure there was an answer.

    I just moved into a new apartment. Brand new, never been lived in before. This is pretty much a sure bet that all the windows, weatherstripping and insulation are good.

    The Air handler is located in the attic along with all the ducts. The compressor is located outside.

    The compressor is a Goodman Model # CPLE24-1C.

    I have a 1350 sq ft aparment.

    The problem is that the A/C literally almost never shuts off. I have it set at 68 degrees. By about 3 in the morning it finally gets to 68 and shuts off. By noon the temperature outside gets to 90 and the inside temperature keeps rising up to about 80-82. Once the sun goes down the internal temperature slowly drops back down to 68.

    I called the landlord who called the A/C guy who came and gave me a what I think is a line of crap. He tells me that 68 is ridiculous that I should set it at no lower than 75. I told him that even 75 is a moot point because it won't go lower than 80 in the apartment during the day. He went up into the attic to look at the air handler. He says everything is fine there. Checked the freon. He says it's good there. He told me that I'm going to just have to live with the fact that on a 90 degree day it's not going to get down to 68 degrees. I told him that it's not even getting down to 75. He told me that noone else in the complex is complaining. Everything up in the attic is fine, the freon is fine and I pretty much need to quit complaining. Well I am going to complain. I moved in 3 days ago and the A/C has practically never shut off. I have it set at 68, but it rarely even drops below 70 in the apartment.

    Now here is my theory from reading some of the posts on this great site. I think it might be a duct problem. During the night the air blowing from the vents is semi-cool. During the day the air blowing from the vents is room temp. Every vent seems to be blowing a different temperature. One vent is barely blowing anything. Keep in mind that I know very little of A/C, but does this sound like a ton of leaks in the system?

    I am very concerned because this new place costs $200 more a month in rent than my old place which I can barely afford. I don't want to even think about the power bill. I bought a window air conditioner for now before I consider what I'm going to do next. I know that the A/C guy that came here told the landlord I was nuts. But I think he is trying to avoid going into the 130 degree attic to do some ductwork while the work is still under warranty I assume.

    What do you experts think? I'm sweaty and at my wits end.

  2. #2
    Join Date
    Dec 2003
    Location
    Corpus Christi TX
    Posts
    206
    The duct system probably isn't designed properly but that probably isn't the cause of the poor cooling. A 2 ton system on that size apartment sounds rather small to me but hard to tell without specifics. If you measure the temperature of the return air minus the temperature of the supply air from one of the registers, this will get you your temp drop, and if your within 15-20 degrees thats probably as good as its gonna get. The system very well may be working fine as he said and would probably work o.k. in a smaller apartment. Unfortunately, apartments get their AC installed by the lowest bidder, and lowest bidders don't like going back and fixing stuff.
    Big leaps get you there faster, small steps keep you there longer.

  3. #3
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    Jul 2005
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    40
    How do I measure supply and return air?

  4. #4
    Join Date
    Aug 2004
    Location
    Tyler TX
    Posts
    676
    with a thermometer
    HVAC Contractor, Tyler Texas.

  5. #5
    Join Date
    Jul 2005
    Posts
    40
    What kind of thermometer? All I have is a thermometer to take my temperature will that work?

    And should I do this in the middle of the night when it's cool in here and the supply air is cool. Or during the day when the supply air is warm?

  6. #6
    Join Date
    Mar 2002
    Location
    Concord, CA
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    2,633
    68 degrees is absolutely ridiculous in the sense that a proper system is designed for 75 at design conditions. At least that much of your tech’s story is not BS. But as you say it's a moot point because it can't even maintain 75.

    Your duct theory is very familiar to me. I wonder why? :^) The ducts may not be the complete story but I can almost guarantee you they're a part of the story.

    Temperature drop is also a part of the story but not the complete story. Go ahead and measure it. If it's off then that's a sign of trouble. But even if it's spot on then that's not necessarily a sign of no trouble.

    Here's the deal. Read carefully and s-l-o-w-l-y. I'm not trying to sound patronizing but for some reason this just goes right over too many people's heads. What your AC guy did was "check the box". In other words he took a bunch of mechanical readings and declared it OK. That's what most techs are trained to do. And most of the time that gets us by. But the funny part is that for all the readings he took he still has no clue how much air conditioning the system is delivering.

    This is how you measure the unit's output: You measure the temperature drop (TD). You then measure the delivered airflow in cubic feet per minute (CFM). You multiply those two numbers by themselves and 1.08. In other words the formula is CFM x TD x 1.08. That's it. There's nothing else. IF the system is delivering 2 tons worth of air conditioning then it's undersized, period (assuming that your story is accurate). If it’s not then you need to find out why. But the tech that just visited in fact has no clue what the delivered tonnage is.

    If you want real nitty-gritty... At best two tons (24,000 BTUs per hour) would measure as a delivered capacity of just under 17,000 BTUs per hour. That's because an air conditioner typically loses 25% of its capacity to moisture removal (which is usually a good thing). And it loses another percentage to duct losses. California Title 24 calls for 6% maximum on new construction. So I used that number. But most of the time losses are higher than 6%. Come October Title 24 is going to require existing systems be less than 15% in many cases. So with a 15% duct loss your delivered capacity would be 15,300 BTUs per hour. I’d bet that your delivered capacity is not even close to that.

    Measuring delivered output is a pain in the arse. Few guys even have airflow hoods on their vans. That’s why checking the box is such a routine and attractive thing to do. If doing so finds the problem then great. But if not then that’s when I suggest measuring output. If actual output is measured then that provides a very powerful argument for one side or the other.

  7. #7
    Join Date
    Jul 2005
    Posts
    40
    I say 68 isn't ridiculous because I've never had a problem in all my A/C life maintaining that temperature in all different kinds of dwellings.

    The A/C guy wasn't in the attic more than 30 seconds. He said a posssible problem may be that the installer left the panel off as he has discovered this problem in the past. He went up there looked at it and came down.

    If it is undersized it won't blow any cool air? Also why does some vents have different temperature air? And why is one vent that is relatively close to the Air Handler blowing VERY little air?

    I'll call the landlord again who will call the A/C guy again. Who will come to my house again and give me a line of crap again.

    I know one simple fact though is that even if I want to set it at 75 and it won't hold 75, that there should mean there is a problem? Correct?

  8. #8
    Join Date
    Mar 2002
    Location
    Concord, CA
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    2,633
    You better thank me for all the time I'm putting in for a complete stranger.

    The fact that many systems will maintain 68 is indeed a fact. But that's because most systems are moderately to grossly oversized. This too is a fact that has been well documented. A right sized system is typically designed to maintain 75 at design conditions. Design in my area is 97 degrees outdoors. It's going to be different for your area.

    Undersized simply means it isn't a big enough AC for the home. And undersized AC will still deliver nice, cold air – just not enough of it. Obviously I don't know if it is or isn't undersized. But IF it is delivering two tons of air conditioning (which we don't know yet – but I showed you how to determine that above) and IF it can't maintain 75 degrees inside at your area's outdoor design temp then it is undersized.

    So yes, if it won't hold 75 at your design temp then it IS broken or undersized. What area do you live in?

  9. #9
    Join Date
    Sep 2004
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    3,157
    Here's the deal. Read carefully and s-l-o-w-l-y. I'm not trying to sound patronizing but for some reason this just goes right over too many people's heads.

    yea it sure did

  10. #10
    Join Date
    Jul 2005
    Posts
    40
    Southwest Missouri

    And it can't even hold 80.

    Could the landlord make them redo the A/C. Properly size it? I just know that with as little help as the techie was the other day. I'm not going to get him to do all those tests to see if it is in fact delivering 2 tons. And the techie that came was the owner of the HVAC outfit.
    I haven't thought about the oversized units in my other places I've lived. It makes sense that I was able to maintain 68.

    I do not want to move. I do not want to move.


    Thanks for the help so far irascible.



  11. #11
    Join Date
    Mar 2002
    Location
    Concord, CA
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    Well I tell you. There's something really wrong when an HVAC owner/operator says it's fine but it can't even hold 80 degrees. Either you're nuts or he's incompetent.

    Anyway, what city and/or what's the nearest major city? I just went through the sample cities in my software for Missouri. The lowest design temp was 91 degrees. That would mean that in the worst case scenario the AC should be able to hold 75 inside when it's 91 outside.

    Something else to keep in mind: I don't know this for a fact. But it's VERY likely that unit was designed with the idea that there is no load under your apartment. In other words, they probably assumed that the space below was going to be maintained at a similar temperature as your space. If that were true then the guy below would only contribute a small amount of heat to your apartment. But what if the guy below you thinks 80 degrees is very comfortable while you're trying to maintain 68 degrees? It means that he'd hardly ever need to turn his AC on. Since hot air rises and cold air falls the guy below you is getting a free ride.

    I don't know why I didn't think of that sooner. I very routinely tell people that live in upstairs apartments that they're going to pay the AC bill for the guy below and that the guy below is going to pay their heating bill. It's an exaggeration of course. But it's largely true. Guess which one gets the raw end of that deal? That's right! You. Good luck trying to work with the guy below you on that.

    You may yet have a combination of undiagnosed problems including ducts and whatever. But the upstairs/downstairs thing is going to be a huge factor if the guy below you likes warmer temps and/or isn't home much.

  12. #12
    Join Date
    Jul 2005
    Posts
    40
    Not incompetant. Just doesn't want to do all the work you described above. Probably for free under warranty.

    I'm in the Springfield area of MO.

    I don't know about the people below me. All the A/C's are the same size here the upstairs and down.

    My main deal here is that when I call the landlord I want to know somewhat of what I'm talking about so THEY, the landlord and techie guy doesn't think I'm nuts.

    I don't know what to do. I just know my power bill will break me.

  13. #13
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,633
    HVAC-Calc says your design temp is 93 degrees. So it should be able to maintain 75 inside when it's 93 outside. That would mean that once it gets above 93 outside the temperature will start to creep above 75 inside.

    Don't discount the upstairs/downstairs thing. It's likely to be a big part of your problem.

    What to do? If it is a fact that the unit won't maintain 75 inside when it's 93 or less outside then demand it be fixed. There are laws about rentals being livable. A landlord doesn't have to paint walls. But the law is clear that he has to keep it livable. That means working plumbing, no infestations, working HVAC, etc. You have the law on your side in that regard. Well at least in California you would. I don’t know about Missouri.

    And the other thing to do? Move into a downstairs apartment ASAP.

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