hvac help please!
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  1. #1
    If anyone can help me here I would appreciate it! This is the same problem I had last year. As soon as the temp. outside gets about 88-90 degress and then definately above 90 I have been having problems!!!!!!!!!! what happens is that the unit cycles on about 9:00 am and runs to about 10:30 pm. I have it set on 72 and the in room temp. rises to about 77 or 78 and the spends the night catching up and eventually cycling off about 10:30 or 11:00 pm. First I will rule out all the obvious. Nothing has changed, no new roof, no trees have been cut down, etc. I have had technician after technician come by and they all hook the gauges and the unit is not over or under charged, it seems to be running perfect. inside the temperature diferential from the closet register to the return is good. all filters are clean and the air flow is good, also does not need a new thermostat.
    any help will be greatly appreciated!

  2. #2
    Join Date
    Nov 2004
    Location
    SW FL
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    6,225

    Lightbulb A Tad Warm

    Originally posted by hotinthesouth
    then definately above 90 I have been having problems!!!!!!!!!! what happens is that the unit cycles on about 9:00 am and runs to about 10:30 pm. I have it set on 72 and the in room temp. rises to about 77 or 78 and the spends the night catching up and eventually cycling off about 10:30 or 11:00 pm.

    Don't tell me, it's a RHEEM.

    Undersized System(s)?

    Leaky windows and/or doors?

    A lot of East Facing Windows?

    More than average area of West facing Windows?

    Do you live in a glass house with CLEAR ( no tint) windows?
    "Glass house " = > 25% for Glass to Floor Area ratio.
    i.e. 700 Sq. Ft. of Glass in 2,500 Sq. Foot home.

    Age of residence
    Location
    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

  3. #3
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,633
    Your technicians are doing what they were taught. They're "checking the box". In other words if the machines are running correctly than the system must be running fine, right? But of course you know that to not be true.

    Is the machine big enough? You couldn't know that for sure unless a heat load calculation was performed. That can take one to several hours.

    Is the machine delivering the capacity it's rated for? Taking the temperature drop does NOT tell you that. You need to know how much air volume the system is delivering, the temperature at which it's being delivered (that much you know) and how much humidity is being removed. Only then will you know if it's delivering what it's supposed to. And if it's not, you've got a bunch of issues like undersized and/or leaky ducts, undersized refrigerant lines, equipment size, etc. to look at. Again that can take another one to several hours to figure out.

    Most techs don't look at those things because they don't know how or aren't equipped to. But even when they do, a lot of customers have the notion that diagnosis should be quick and cheap. With all those companies offering diagnosis that are "free" with repair, they can't be blamed. But the reality is once in a while a diagnosis can take hours and cost hundreds.

    If you think that system ran great the year before and that therefore it has to be some sort of easily diagnosed failure, you might be right. But whatever the case may be you obviously need someone to look beyond the box.

  4. #4
    Join Date
    Apr 2004
    Location
    Niantic, Illinois
    Posts
    545
    As stated above I agree. I would just like to stress properly sealed, insulated, and sized ducts. Poor duct systems will harm the performance of the best units.

  5. #5
    Join Date
    May 2003
    Location
    Sarasota. Fl
    Posts
    1,232
    Old leaky windows?

    A "smoker" constantly going outside to smoke?

    Kids running in and out?

    Lack of insulation?

    If the "charge" is correct your probably gaining to much heat for a variety of reasons?

    Has anyone looked at your duct work?

    You need a good tech ......

    And a few hundred dollars for a correct diagnoses. (not including the repair)

    Good luck.




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

    ~Albert Camus

  6. #6

    yes miami mike it is a rheem

    also it runs fine on an overcast day plus during the morning and night, it is only when the sun is out and about 90 plus degrees. But every theory I can think of doesnt make since when I consider the fact that it ran fine the first two years I lived here. I have two more questions. first, what about insulation in the attic? I have the same amount that I did before and it is a decent amount but if I add more will it make a significant difference? also I have a set of pancake vents that have exhaust fans attached but are not hooked up, would they make a difference?

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,579
    More attic insulation will help.

    Hooling up the power vents will also help.

    If the exsisting attic insulation is blown insulation, it may have settled, loosing alot of its r value.

    In the 4 years you have lived there, have the coils been cleaned.
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    How many times must one fix something before it is fixed?

  8. #8
    Join Date
    Nov 2004
    Location
    SW FL
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    6,225

    Question Re: yes miami mike it is a rheem

    Originally posted by hotinthesouth
    also it runs fine on an overcast day plus during the morning and night, it is only when the sun is out and about 90 plus degrees.
    Your SYSTEM ( Condenser - Air Handler - Building envelope) performance has obviously deteroriated ~20% + " in the 3rd and 4th years" based on your statements.

    RHEEM ( The Green Box mfg) is one significant LONG Term concern IMHO.

    "But every theory I can think of doesnt make since when I consider the fact that it ran fine the first two years I lived here. " : HotinTheSouth

    Have high quality ( MERV 7 or 8 : ~30 % + efficient ), pleated filters been used since day 1?

    Rephrasing:
    Did you use blue ( Low {or no } quality ) filters for the first 3 years?

    Even a slight amount of dust/dirt would make your coils > 20% less effective.

    Has anyone been in the attic ( to "dent" / misconfigure the flexible duct) prior to the 3rd year of operation?

    Review of coils, duct work integrity and Attic Temperatures does not appear to be as THOROUGH as necessary up-to-this-point.

    If your air flow is not measured, you can NOT say ( know )
    It is Good.

    BE THOROUGH & Persistent !
    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

  9. #9
    Join Date
    Nov 2003
    Posts
    125

    Confused

    Is the air handler in a closet,attic,basement?

    If it's in a closet like most of them are here in east Tx.,is the bottom of the closet under the platform sealed off?

    Sounds like open duct sucking hot air somewhere.

  10. #10
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Many Rheem air handlers require that the first couple of feet of suupply duct ,be the size of the blower "takeoff" for proper air flow.There may also be "tabs" at this point that Must be bent up ,per the tag on the tab.


    Both of these requirements are commonly overlooked by the installers,in our area.

    Either will result in low airm flow,and low capacity,plus improper charge,making it even worse.

    Can you post the model of the air handler?Type of duct?

    Picture would be great.

    If the supply duct is the size of the air handler,you likely have this problem.If so it's a simple fix.

  11. #11
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,271
    Your technicians are doing what they were taught. They're "checking the box". In other words if the machines are running correctly than the system must be running fine, right? But of course you know that to not be true.
    I've been in a similar spot as hotinthesouth more than once. Two instances were in apartments, one I was renting and the other at a complex where I worked.

    In the second instance, the tenant would tell me that during the morning and late evening hours, the system cooled just fine, but in the heat of the day, it "just lays over and dies", to quote him. It didn't quit cooling, but it sure couldn't keep the apt nice and cool like both of us thought it should.
    Now back in these days I wasn't as hip on subcooling and superheat as I am now. Even so, just checking the pressures (i.e. checking the box) didn't satisfy me, because the pressures looked "fine" no matter what time of day I checked it. But I could at least prove to myself by using a temperature probe that the discharge air temperature at the evap deteriorated at midday. It was then I noticed traces of oil around the piston. I pulled the charge, fixed the leak, then pulled out a piece of trash from the piston. The piece of trash that was not allowing the piston to seat properly, thereby flooding the evap just enough so that when the indoor heat load and outdoor ambient temp outdoors rose, the mass flow rate through the evap was aggravated by the piston that wouldn't seat all the way. I pulled the trash out, evac'd the system, charged it up, and from that day forward I had one VERY happy tenant.

    In the first instance, it was at an apartment I lived in while working as a service tech in San Diego County. I couldn't seem to convince the management and maintenance guys that my unit lost capacity during the heat of the day. Nothing wrong with the ducts or airflow...same as in my first example above. I at first withheld from doing anything with the system as I was paying rent for these guys to worry about that...why should I after being on rooftops and in attics sweating over everyone else's units all day?
    Finally I went up there and stuck my gauges on it and instantly saw a compressor with diminished capacity. I leaned hard on them and they got me a new compressor.

    Anyway, I said all that to say there's certainly more to this trade than "checking the box", especially in the first example. The problem wasn't in the box, it was in the flowrater "outside the box".
    The second problem was inside the box but getting apartment maintenance techs to understand how a compressor can have diminished capacity yet still cool is like getting every American to view every political issue exactly the same way....won't happen!

    Looking back, both situations could've been nailed merely by checking superheat and subcooling! How many "box checkers" do that???
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

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