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Temp of air coming out of vents...

tbritt
June 23, 2010

I have a Goodman GSC130361, 3 ton ac unit. The air coming out of the vents is 66 degrees. I was told by the company that installed it, that the air should be between 50-55 degrees. That is a big difference. They came yesterday and checked the freon in the unit and we changed the filters. When they left, the air blowing in was at 62 degrees. The guy said it should continue to go down toward the 55 degree mark.

Well, today it is at 66 degrees. I called them and they are coming back tomorrow. My neighbor has a 2.5 ton Lennox and he is getting air that is 55 degrees coming into his home. When they checked my unit yesterday, they said the freon was good and the unit is charged. What could be the problem? Oh yeah, the unit is less than 3 years old.

Comments (51)

  • weedmeister

    what you want to know is the difference between the inlet temperature and the outlet temperature.

  • david3303

    I am in Oklahoma. The temperature is 100 degrees outside. How much difference in air temperature should a central air unit be able to generate?

  • tima9209

    Depends not only on the HVAC system but how well the house is insulated, how tight it is WRT things like ceiling penetrations and windows, and factors such as shade trees. That said, I would be rather displeased if my house in So. Louisiana couldn't maintain 75F on a 100F day. I have no shade to speak of, and I have R-38 blown-in insulation in the attic. The HVAC is a Goodman 3.5 ton system (3 y/o). These past few weeks of 95F+ days, it's been maintaining 72F.

  • tbritt

    tima9209, how cold is the air coming out of your vents? How many sf is your house?

  • tima9209

    The temperature of the air coming out of the supply registers is usually about 15-20F below what it is at the return. Right now, it's about 56F, and it's 73F at the return. Like the other guys said, the absolute temperature doesn't mean anything. What important is the difference (or "split" or delta-T) between the return and the supplies. How you measure the temperature is important. If you care about accuracy, don't use an I/R point-and-shoot thermometer. You need to insert a traditional thermometer into the register and let it sit there for a few minutes before reading it.

    P.S. As I tried to indicate in the subject line, the forum software gave me a bizarre error message:

    "Message Rejected
    You already have a follow-up listed with the same subject. If you didn't see your message listed, you probably need to reload the page.

    If you want to submit another follow-up to the same message, please change the subject line."

    That is hands-down the weirdest requirement I've ever seen from any forum software.

  • tbritt

    My air out the supply vent is 66F, at the return it's 76F. Thermostat says it's 80 in the house and it has been that way for the last 6 hours. I did use a regular thermometer for the readings. I don't believe my unit (Goodman GSC 130361) 3 ton, is blowing air that is cold enough. It has been hot here the last few days (mid to upper 90's) but, this unit should be blowing colder air. My air guy says it is running the best that he can get it. The unit is less than 3 years old.

  • tima9209

    Your story is very familiar to me. If all else fails, call a different HVAC company. I bought my house new a few years ago, and like yours, my AC never worked well enough. I had the installers out three times (installation warranty, you know), but they never could get the thing working right. I called another company the following summer, and their tech got it working fine. You'd think any HVAC tech could charge a system properly, but unfortunately, that is not the case.

  • srercrcr

    The issues are (1)the temp of the conditioned air, could be low on freon which would indicate a leak requiring fixing. You might just feel the temp of the exhausted air from the condenser just for grins and cost nothing...should be very warm, bordering on hot. Also, is the big copper like going into the wall very cold and very wet? (2)the delivery of the conditioned air, which may be suspect. Are you getting a good strong flow from all registers? If not you could have duct leaks, dirty filter or indoor coil (3) environmental issues...system is undersized for issues like excessive direct sun window or wall exposure, inadequate attic insulation or ventilation, owners asking for cooler temps than system was speced for, hotter outside temps than designed for.

  • weedmeister

    A 10deg drop is a bit low. Mine is more like 20F. YOu need to call someone else to check charge while running and blower speed (too high, too low, etc).

  • creek_side

    I agree, ten degrees sounds low IF you stuck the thermometer into the register so that it is reading only the supply temperature and not a mixture of supply and room air, and only if you used the same thermometer to measure both return and supply air temps.

  • mark40511

    Speaking of supply air and return. Please enlighten me. Are you saying that the supply air is the air being sucked into the intake (where the filters are that we change).....Isn't that "room temperature air"....so if it's 75 degrees in the house, isn't that the "supply" temp? Why would the supply air be any different than the air that has already been conditioned? That's what's going into the supply, the conditioned air...Right?

  • weedmeister

    Air being 'sucked in' is 'return' air, air that is returning to the unit.

    Air that is being blown into the room is 'supply' air, air 'supplied' to the room by the unit.

  • mark40511

    That's what I meant. Sorry I think I have it! Say the temp inside is 77 with the A/C currently running full blast......The air coming out of the vents should be 15 to 20 degrees cooler than the "room temp" air (basically what's going into the intake)...Thus, in that scenario, the air temp coming out the the supply would be 57 to 62 degrees and be considered working properly. So the air temp coming out of the supply actually changes with varying room temp, yet is still working properly, as long as it's 15 to 20 degrees difference. No more/no less..........If it's MORE than 20 degrees that could indicate a problem as well......(although for a/c.....One would think you would WANT the coolest air coming out....(the lower the better one would think) but that's not the case......Right?

  • busboy

    Is your ducting in an attic? A hot attic will lower the temperature spread. If so, check the spread at night after the attic has cooled. Mark is right about 20 degrees and more spread..the heat exchanger will ice up.

  • tgmccallie

    I just had a energy survey by my local power board and they checked the difference between the register and return temperature and found it to be 22 degrees. They said that they wanted it to be around 15. They said that the 20 to 22 degree difference indicated that my unit was not operting at peak.

    With this informtion as it was they went under my floor in the crawl space where my duct was and we found it to be cooler than my house was inside. He checked the duct and found several air leaks where the supply duct hooked onto the trunk. He also found a place where a hole had been cut and patched and the patch had come off allowing a hole about 4 x 4 inches.

    He told me to go to HD or Lowes and get some duct sealing paste and oat over these air leaks I might add that after he left I found several more supply lines that were leaking and one had come loose from the trunk completely.

    i also found one of my returns not to be closed off at the top but was allowing hot air from the attic to be pulled back through the return,

    I pasted all the leaks and completely sealed up the return.

    How my difference in temp between the floor register and the returns are 15 to 16 degrees.

    The only thing that puzzles me is the explaination of why the returns would read 64 when the temperate in the houe is 76.

    Can someone explain this to me, please as a freind of mine is telling me that the air going back in returns should be the same at thetemperature in the house.

    Advise

  • mark40511

    Wow! You had all those leaks in your ducts and it actually made the temp spread larger......How odd, but I have heard that you want no more of a temp split than 15 to 20 degrees. Now I'm paranoid. I'm thinking of going up to my attic while the A/C is running and checking the ducts to see if I feel any leaks. I don't think there are any..Reason being is that when I go into the attic it is extremely HOT.....I would think if there were leaks it would be (cooling the attic) as well......To me, the air going into the return register should be about the same temp that the house currently is ( I mean it is sucking air from inside the house into the intake)...Since the air being sucked into the intake is coming from inside the house, wouldn't one think that the current temp in the house would be the temp of the air going into the intake? I think it is.

  • countryboymo

    Even if the system is in the basement and the returns are not sealed well from the attic in the wall cavities the air can be pulled out of the attic. I had 78 degree air in the house and 85 degree air at the air handler.

  • khightower3_verizon_net

    OK, I live in Texas. Current temp outside is 102. Current temp inside my house is 86, even though I have the thermostat set at 74. This has been going on for YEARS. My electric bill in the summer is over $500 because of this. I change the a/c filter monthly. I had a new unit installed 5 years ago, but that never resolved this issue. I have a 3 1/2 ton unit (1800 sq. ft.). I have put radiant barrier in the attic and added 5" of insulation. I've also checked all seals for windows/doors. I have installed 90% solar screens on the windows. Nothing, absolutely nothing is helping to get the temperature down in my house. I put a temp guage in the vent located in my dining room at it is reading 90 degrees. I have had at least 4 different a/c companies come to my house and all said my a/c is working fine yet the temperature continues to climb. I can go to other houses of the same size and their house is cool as can be. Can someone please give me some advice? I've been putting up with this for 15 years now and its never gotten any better, only worse. Thanks.

  • qwiksilver

    khightower3,

    Have an energy audit performed on your home. Make sure the person/company that performs the audit does a blower door test and that they use IR imaging to determine where your deficiencies lay. Use a reputable company and you'll know within no time flat where your energy dollars are being depleted/consumed.

    Frank

  • maryland_irisman

    From a long distance perspective, I can give you some advice and things to look at to help narrow the problem down. Without being there, I can only guess at what the real problem is. I can give you, the homeowner, some things you can do. After that and, no improvement is attained, a trained person needs to take it further.

    There are a lot of factors which impact the ability of your unit to pull down the temperatures. The energy audit with IR imaging should certainly be done if unit itself is sized and operating properly but is not pulling the temperatures down.

    You should expect a 15 to 20 degree temperature differential from the air temp going in and the air temp coming out, after the unit has been running a period of time. I suggest you use 2 accurate thermometers. Put one into a return duct closest to the unit as possible. Put another into a supply duct as close to the unit as possible. Doing this right at the plenum is preferred. If you are getting a lot of condensed water leaving the unit, you can expect the temperature difference to be closer to the 15 degree differential range. As the air in your home cools and the moisture is removed, you should get closer to the 20 degree differential range.

    If you have lots of windows and very large windows, you can expect the unit to have a more difficult time pulling down the temperatures. Windows facing the sun all day should certainly have blinds or curtains closed. Many times folks have many plants in front of windows and want the sun light to come in, in addition to keeping them well watered. Also if your windows and doors do not seal when they are closed, you'll get some infiltration of hot humid air that will impact the effectiveness of the unit. Lots of people (kids?) going in and out frequently can have an impact too. If you do a lot of cooking and baking, that surely has an impact. All of the things I mentioned may not pertain to you but need to be mentioned so you can do your own audit before bringing in experts.

    The next issue may be duct leakage. Ideally, the cooling plant should be located in the center of the house. This is not always the case. Units located at one end of the house, trying to condition several floors or just merely the length of the house can have issues also. This is evident when one end of the house or, upstairs rooms aren't as cool as desired. If the unit is too large for the house, you can expect problems also which negatively impact the comfort of your home. Duct sizing and air flow balances can be an issue too.

    So basically, I'm suggesting you do an audit yourself, looking for areas where the building might have problems. That would include heat sources like home electronics, large CRT or projection tv's, etc., and measure the temperature differentials as close to the unit as possible. Also monitor if the unit has a tendency to cycle on and off a lot. Take a look at the temperature differential in the evening and at night too. If it gives you the temperature differential or, close to it, you need to look at insulation and other infiltration problems.

    With all that said, I now look toward the unit itself. My first thought from the information you have provided and, if I discount any and all of the infiltration issues and, if your technicians have accurately determined the unit is indeed functioning with the proper refrigerant charge, etc. then I am suspecting the expansion valve. That's not to say that is what it is, I would have to be there to accurately determine the problem, this is only an educated guess.

    I had a customer some years back complain their unit ran perfectly all day. Then it seemed from 5 o'clock on, the unit just stopped cooling like it should. When I went to look at the unit, after 5 o'clock, the family car was parked right in front of the unit, blocking air flow around the condensing unit. That's where the husband parked the car every day when he came home from work. This proves that many times, a problem is very simple to resolve. Perhaps you should check your condensing unit to make sure it is not obstructed by plants, grass clippings, debris in the coils. If it is under a deck or low overhang, it could be recycling the hot condenser air, not cooling the refrigerant to the required temp. to totally condense all the refrigerant.

    Now if the refrigeration techs. are not competent, then the whole issue could be a little nasty, air in the system causing icing inside the expansion vale, an over/under charge, unit designed to be used in Connecticut instead of one designed for Texas, The list goes on. But from the responsiveness you have expressed these guys have provided you, I'm inclined to think they want to do a good job and want you to be satisfied. Keep calling them out until it has been proven nothing is wrong with the unit itself. They should be able to help you identify other causes, if there are any.

    I wish you luck!!

  • Mjclemm

    Have the same issue, I am not sure of the exact temp comming in or out, all I can say is is not cold enough.. I've been in places that the air is cold, my air is NOT. I have a 17 sq ft house and a 4 ton AC, the unit is only 4 years old and think it should at least cool down the place so it's comfortable, that's all I want ..Mjc..

  • St8kout

    I just had a new rooftop 14 seer Trane installed. Stuck a temp probe in the vent and my digital Fluke meter shows 55.1 degrees as the lowest it will go.

    It's a 3 ton unit for my 1207 sq ft house. Seems to have no problem getting to 78 degrees but trying for 77 degrees (digital honeywell thermostat) takes a whole lot longer runtime. Outside temp is currently 100 here in Vegas.

    It replaced a 27 year old Whirlpool that although still cooled ok, was vibrating the whole house and the gas heater part of it was badly rusted and a carbon monoxide hazard, so it had to go.

    After they left I went up on the roof to take a closer look. Everything looked like it was done correctly and with no roof tile damage (4 people running around up there). Trane uses what looks like Christmas tree tinsel and even though theres a plastic grill to protect it, looks like they stuck there hands in there trying to move the unit around and flattened whole sections of it. Not sure if it's a big deal, but it has to be affecting some percentage of cooling efficiency, however small. It's probably near impossible to stand them back up. With traditional fins you can get a 'rake' from Home Depot to straighten them back out, but not these things. It would be a tedious job and possibly damage even more of them.

  • Pete-in-SoCal

    I have a 4T Carrier unit with an Accu-rater coil (not expansion valve or fixed orifice) evap coil. I am getting about 14 degrees temp drop measured at intake and a close wall outlet (before attic warming occurs).

    1. Under extreme conditions, like high attic temps, does this device limit the cooling capacity of the unit?

    2. Can I improve this number by adding R22?

  • mike_home

    Pete,

    You would get better responses if you started your own thread.

    Are you saying you only get a 14 degree temperature drop when the attic is cool? What is it when the attic is hot?

    You could be under charged, but there may be other problems. I would also check the duct work in the attic. I suspect you have leaks and are losing a lot of cooling capacity.

  • Pete-in-SoCal

    Thanks. I had checked my ductwork a while ago and fixed a number of leaks. I just talked to a AC service Tech who confirmed that the Carrier Accurater that I have is no better than any other fixed orifice metering device, and definitely inferior to an expansion valve.

    We are going to look at the system charge next week.

  • robsamp

    Will appreciate if anyone could give me ideas on why my central a/c is not working as it is supposed to.
    Live in Florida and just had replaced the compressor. Now the place feels uncomfortable, clammy, humid and would appreciate any ideas for the possible reasons.
    The place is a 1100 sf apt in Florida.
    A/C is 17 yrs old, air handler was maintained very well and is in good condition.
    At 11PM the air temperature inside the plenum is 54-56F. In the room it is 76F measured with the same thermometer but it is 70F right before the air handler filter.
    At 3 PM the air inside the plenum is 58-60F, the other two are the same.
    The unit is a 2.5 ton and the used compressor recently installed is a 32000 BTU and is 6 yrs old used.
    I keep the thermostat set to 76F but feels uncomfortable and if I lower the temp to 73, the ambient becomes extremely uncomfortable. If I increase the thermostat to 79F, the feel is more comfortable.
    The humidity fluctuates between 50-54 as per a cheap monitor with +/-10% accuracy.
    The tech already decreased the evaporator fan and said everything was fine.
    Thank you again in advance.
    Rob

  • tigerdunes

    It is considered poor forum etiquette to piggy back onto someone else's thread, particularly one so old.

    Go to main page to bottom of page and start your thread. It is likely you will get some helpful replies and advice...

  • umpfan

    We had less than a 10 degree difference last summer. Our hvac man took the garden house to the outdoor unit and cleaned out the dust/dirt. The temperature difference jumped to 17 degrees in less than 5 minutes. Check youtube for videos on how to do this.

  • udarrell

    The humidity level of the indoor air has a huge effect on the temp-split; at 50% RH the split should be around 19 to 21°F.

    The higher the %RH the lower the split all the way down to around only a 14°F temp-split.

    Take the temp off the outdoor condenser, it will be the opposite the higher the indoor %RH the higher the temp-split will be as it contains the latent heat of condensation on the evaporator fins.

    Tell us what those condenser temps verses the outdoor temp is & the installation date of the condenser or its SEER Rating. This will provide us with a lot more clues as to the problems the system may have.

  • Jeff Jones

    Ok, so maybe you all can help..

    Location: South Forida (just north of Fort Lauderdale)

    Brand new 5ton unit, and outside unit were put in just 2 weeks ago.. 3400SQ FT house


    The old unit was replaced because the tech said the coils were bad, that unit was a 3.5ton unit, and kept the house at 71 degrees when it was 95 outside.

    This new unit doesn't even cool the house to 72 degrees, its always running, my electric bill has gone way up.



  • d2305

    Have them come back or find a good a/c tech.

  • udarrell

    They way oversized the condensing unit; of course the duct system is now way too small to handle a 5-Ton airflow CFM.

    I would make them replace the 5-Ton with a correct sized condenser; probably no more than 3.5-Ton

    Get others to help you do a free online whole house load-calc. Do It...

  • socahomeowner

    I am very detailed. I would appreciate an accurate answer to whom ever has the most knowledge and expertise to give me a DIRECT (sorry I'm so frustrated) answer since we are in the most advanced technology country on Earth (USA) someone should know the EXACT answer to the following:

    1. What is the minimum and the best output temperature should be from the AC air vent or can be?

    2. What is the cubic feet air flow should be?

    3. Like the car AC when you can adjust the air pressure from low to high, how can I find out if the flow of pressure is at high pressure and not low or medium when it comes out of the vent to the house?

    4. Like gasoline for cars that is graded as regular unleaded and premium, is there anything like that for R22 (are they all the same quality or is there a difference that can make the air comes to house to be colder?

    5. Considering all situations and (everything in working order) how many minutes should it take for each one degree of temperature to drop inside the house?

    Thank you deeply for your accurate answers!

    -Southern California Homeowner

  • d2305

    R22 is all the same. The temp should drop 20* after passing through the A coil.

  • kayczak

    From what im learning as a apprentice your supply air and return air should have about a 10% difference

  • mike_home

    So if the return air is 75 degrees, then are you saying the supply air will only be 7.5 degrees lower? That is a poor temperature split in my opinion.

  • Martin Green

    @mike_home... kayczak's "rule of thumb" is useless since neither Fahrenheit or Celsius start at absolute zero, skewing the calculation as the average temp varies. If you apply his rule to Kelvin you wind up with a 53F temp differential, which is also ridiculous. His method might be workable with Kelvin calculations, but 10% is WAY too high. 3% would be more reasonable.

  • Ron Roth

    There is a company that makes a generic HVAC monitoring system that measures/records Inlet and Outlet temperature -- see www.mhvacmonitor.com

  • udarrell

    The percent of relative humidity has the greatest effect on the indoor SA/RA temp/split.

    At 50% RH the split should be around 19 to 21°F.
    Higher humidity above 50% yields a lower temp-split; lower humidity below 50% yields a higher temp-split. You have to know the relative humidity &/or also both the wet bulb & dry bulb temps... airflow CFM isn't much of a factor unless it is way-off...!

  • Harold Anderson

    ? Return vents needed? Is the singie retun at the filter sufficient?

  • tigerdunes

    Depending on size of AC unit. You need a minimum return sized correctly for 400 CFMs/ton. However one return may be adequate but can be noisy. I prefer more than one return strategically located for improved airflow and comfort.

    IMO

  • udarrell

    When the units are 2.5-Ton & larger I want two large returns & large grilles; also must have two large return-air filter areas. The lower you get the return-air resistance the easier it is for the blower wheel blades to pickup & move air from the rooms into the supply-air side resulting in increased static pressure at the supply diffusers. That is what you want toward achieving real efficient increased airflow to & from the rooms...

  • udarrell

    Jeff Jones' Post:

    [QUOTE]Ok, so maybe you all can help..

    Location: South Florida (just north of Fort Lauderdale)

    Brand new 5ton unit, and outside unit were put in just 2 weeks ago.. 3400SQ FT house

    The old unit was replaced because the tech said the coils were bad, that unit was a 3.5ton unit, and kept the house at 71 degrees when it was 95 outside.

    This new unit doesn't even cool the house to 72 degrees, its always running, my electric bill has gone way up.[/QUOTE]

    Someone is crazy; U can't put a 5-Ton unit on an existing 3.5-Ton system that probably didn't have enough airflow & proper duct sizing & large enough Return-Air filter areas for the 3.5-Ton unit...!

  • Arnel Lim

    tbritt,

    Did you ever solve your problem. I have the exact same symptoms. I had a tech come over, and all he did was keep adding refrigerant. He would add, check the inlet/outlet temp, then keep adding and keep checking. Outlet temp hit about 64, inlet temp was about 78, and this is after he said he added 3+ lbs. He said that there was probably a "blockage" which was why adding more refrigerant didn't bring down the outlet temp. He also said outlet temp "should" be around 55 degrees. The outlet temp was about 64 at all registers, even the ones closer to the evap. The evap is in the attic.

    He kept suggesting a "blockage" without checking anything else outside of the compressor outside and the register temp. He didn't go into the attic to look at the evap or check for leaks. He was suggesting that I talk to Sales and get an estimate on a full replacement, because that's the only way to deal with a "blockage"

    After adding all the refigerant and running my unit for 3+ hours, my Master bedroom would not cool below 77 degrees. It was about a mild 82 degrees outside (California 82, so no humidity).

    I have a 2.5 ton unit servicing the upstairs and a 3.0 ton unit the downstairs, both running at the same time. Downstairs cools to a comfortable temperature, but upstairs is still uncomfortably hot, even with both units running.

    I went through this exercise 5+ years ago, and all the techs do is add refrigerant and shrug their shoulders. How do I found someone that actually knows how to diagnose this, apart from suggesting I rip and replace?

  • udarrell

    It is an extremely sad situation; a refrigerant system restriction is quite common & can be effectively dealt with.

    The lack of expertise is pitiful...!


  • foreveramarine46

    Before my cooling season begins , I use a product made by Frost King , called Air Codtioner coil foam cleaner ($2.99 a can in home depot or lowes ), you spray it on the coils on the outside compressor, and forget it , I also clean the "A" coil inside the plentum of the furnace, again just spray it on and the condensate will allow the dirt to flow right off, you will, defiantly see an improveent in the Cooling ability of the unit and a reduced Electric bill ! This foam cleaner can be used on window air conditioners, tge surface of car radiators and many more things.

    I also use a 3m filter it' s the Healthy living #

    2200, it will keep your "A" coil in the furnace Plengum very clean, your house A lot less dust in it ! And you will have cleaner air to breath! I change mine every 3 months ,year round ! They are a little pricy, like A 3 Pack for $34.00 in Costco $29.00 when they have a sale on them. The more dirt you let into the furnace the faster the moving parts , blower ECT will fail on you .

  • Ray

    A homeowner's central air conditioning unit is essentially two separate systems. One part of the system provides a means to cool the air (the compressor and refrigerant), and the other part of the system moves the house air through the cooler and ductwork to cool the air (the blower).

    Many times all an air conditioning service will do is check the operation of the refrigerant system. They'll check the freon pressures, perhaps add some freon, tell you it's working properly and hand you a bill. Technically, they check the refrigerant portion of the system and if it meets their specs, it's good. Oftentimes their work doesn't solve the problem as the refrigerant system will be found to be working correctly.

    Here are a few pointers to consider before calling a repairman:

    If, when the house feels cool but it's uncomfortable clammy, the drain from the cooling coils is probably plugged up. In normal cooling operation moisture in the house condenses on the cooling coils and it drains to the outside of the house. All of the dust and stuff that makes it past your ac filter collects on the cooling coils. Most of it flows down the coils with the condensation it and passes down the drain pipe but when the ac unit is not used it dries into flakes and sluffs off the next year. The stuff that sluffs sometimes plugs the small drain line and water backing up in the cooling coil drain pan will pass that moisture back into the house. Dry air feels cooler than moist air at the same temperature.

    IF your supply registers are in the ceiling and the ac is running and the house doesn't cool, a duct supply hose in the attic may have come loose. Air from the house is blown into the attic which lowers the air pressure in the house. Cool air will be coming from all of the registers but one. This results in air from outside the house being sucked in through every crack it can to replace the air that is going into the attic. This can result in extremely high electric bills. If this happens in the floor, the same thing will happen only the air will smell musty.

    I once found an attic mounted central air blower unit with large holes in the suction side of a friends house. She said she couldn't afford to run her air conditioner due to $500/month electric bills. She said she had paid for four visits from an air conditioning company in town and nothing they did helped - they just kept telling her it was working properly. She said all of the air that came into the house was hot and it was cold in the winter when the heater was running. What she was doing was sucking hot (summer) or cold (winter) attic air into her unit and blowing it into her house. For less than $10 in supplies I repaired the holes and other leaks and her bill came down to the $120 range.

    As a summary, oftentimes a poorly operating air conditioning system is the result of a defective delivery system and not the refrigerant system, and many of the air conditioning people will only check the refrigerant part of the system. Their income relies on the number of service calls they make and checking freon pressures and cleaning the outside coils is a fairly easy job. Tracing air leakage through ducts under a house or in an attic can be a long, dirty and very hot job.

  • HU-8397156083

    I had a similar situation occur today. South Florida 86 degrees and cloudy. The temp would not go down under 80 and humidity climbed to 73%. I measured split and it was 12 degrees. The air out of the compressor was 100. So it was working but slightly under its optimal efficiency. I had A bunch of fresh insulation installed last year. It’s been running fine until today.

    I had a friend bring over her dog to play with my dog this afternoon because the park got rained out. So I closed all the doors to the bedrooms (4). When she left I opened all the doors. In about 30 minutes the temperature dropped to 77 and the humidity is now 47%.

    I have fairly large spaces under doors for return. Obviously not enough :(

    I have a 4 ton Goodman that was an upgrade from a 3 1/2 Amana. I had ducts redone at that time to accommodate the increased airflow. I also moved the return to the ceiling via a 20” duct. The opening is 18x36 which should be adequate for 4 tons. I’m considering adding another return in the ceiling but it’s pretty quiet now. Slight airflow noise when fan it on high.

    So just adding this as a possible cause. Restricted return in my case was the culprit. I’m going to measure the split later again to see where I’m at with all the doors open.

  • mark40511

    Same thing with mine for years. I have a single story 1375 sq ft house. If, during the worst part of the day 3 to 8 pm, and it's hot AND SUNNY out, and someone shuts the master bedroom door, the temp will climb a few degrees and the unit will run constantly. But if the doors remain open, it's no issue. So we just make sure never to close the master bedroom door during those hours (if it's hot and sunny out).) However, if it's cloudy out, it's never an issue. It can be 85 and cloudy, and the master bedroom door closed, and it's fine. It's just the hot sun beating down on the house that overwhelms mine if that master bedroom door is closed.

  • Bill Price

    Some of these comments are reiterated again and again. I am a retired HVAC/R professional with over 40 years experience. There is no cut and dried answer to most of these questions. Most of the answers are mostly correct in that you need to seal your ductwork, insulate it if it is in non-conditioned space (attic/crawl space), and the ductwork needs to be laid out correctly to supply AND return the correct amount of cfm to each room. After that, NO air conditioning technician in the world can correctly diagnose an air conditioner's problem unless several criteria are met. First and foremost, BOTH the condenser coil and the evaporator must be clean and the furnace (air handler) filter must be clean and not restricting flow. If you call a company out to your house and the technician comes up to your house with his gauges and refrigerant tank FIRST THING and immediately hooks the gauges up and starts putting refrigerant in, my advice is not to call that particular company back again. The coils MUST be clean before you can even begin to decide that the system is under or overcharged. Next you must make sure that you are moving the correct amount of cfm for the size air conditioner you have. 400 cfm/ton is the nominal amount for air conditioning. NOT ONE person has mentioned how important this is. On MANY occasions, I have seen brand new equipment installed and no one can figure out why it won't work! With brand new equipment, we know the coils are clean so that is not the problem. Let's say we have a house that is 2400 square feet and a new furnace and air conditioner are installed. It's a 105,000 btu furnace and a 3 ton unit. The homeowner complains that their old furnace and a/c (same size) worked fine until they had to have it replaced. Technician after technician comes out.....they hook up their gauges and add and remove refrigerant and can't figure out what the problem is. The a/c runs almost all the time and the pressures are correct but the relative humidity in the house is REALLY high and they can't figure it out. Some technicians recommend a whole house dehumidifier as a fix. C'mon people, let's not put a bandaid on this problem. What most technicians tend to forget with an installation of new equipment is that the new furnace doesn't KNOW what size air conditioner it is being mated with! The new furnace can typically be mated with (and has the blower assembly to work with) anywhere from a 3 ton to a 5 ton unit. These furnaces will have as many as 6 different speeds for the drive motor. A 5 speed motor is more typical but the factory sends these furnaces out USUALLY with the lowest speed set up for heat and the highest speed set up for cool. This means with the 3 ton unit (which needs 1200 cfm delivered), on the highest motor tap speed from the factory, the furnace is delivering 2000 cfm or more! Moving 2000 or more cfm through a 3 ton evaporator will result in a "delta T" of 10 degrees or less which explains the unit running almost continuously and the high relative humidity in the house. These technicians need to remember that they need to look in the installation manual to find the right motor tap speed to utilize with the size a/c being mated to the furnace. With the advent of the 95+ % furnaces, we are seeing ECM motors being deployed in the furnaces. These have no speed taps, but instead have a motor that is in essense a variable speed motor. The technician still needs to consult the installation manual as the motherboard in the furnace will have dip switches to set the motor drive unit to supply the desired cfm.


    Now, some "rules of thumb." IF your coils are clean, IF your furnace filter is not clogged up with dirt and providing a restriction, IF you are moving the correct amount of cfm for your size a/c, IF the superheat is correct and IF the subcooling is also correct, you should get a delta T of between 17-22 degrees and your supply temperature should be between 51-55 after the unit has run for 10 minutes or longer.

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