Temp of air coming out of vents...

tbrittJune 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.

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The outlet temp tells you nothing without the inlet temp.

The temperature "split" tells you if there is a problem.

Your system should still be under warranty...

    Bookmark   June 23, 2010 at 11:25PM
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what you want to know is the difference between the inlet temperature and the outlet temperature.

    Bookmark   June 25, 2010 at 1:02AM
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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?

    Bookmark   June 25, 2010 at 6:38PM
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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.

    Bookmark   June 25, 2010 at 8:03PM
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tima9209, how cold is the air coming out of your vents? How many sf is your house?

    Bookmark   June 25, 2010 at 8:14PM
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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.

    Bookmark   June 25, 2010 at 8:55PM
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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.

    Bookmark   June 25, 2010 at 9:55PM
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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.

    Bookmark   June 25, 2010 at 11:30PM
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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.

    Bookmark   June 26, 2010 at 5:56AM
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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).

    Bookmark   June 26, 2010 at 2:35PM
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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.

    Bookmark   June 26, 2010 at 5:50PM
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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?

    Bookmark   August 11, 2010 at 3:01AM
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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.

    Bookmark   August 11, 2010 at 7:24AM
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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?

    Bookmark   August 13, 2010 at 5:33AM
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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.

    Bookmark   August 13, 2010 at 10:53AM
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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.


    Bookmark   August 13, 2010 at 7:08PM
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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.

    Bookmark   August 14, 2010 at 4:48AM
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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.

    Bookmark   August 14, 2010 at 11:42AM
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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.

    Bookmark   June 17, 2011 at 7:12PM
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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.


    Bookmark   June 17, 2011 at 11:09PM
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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!!

    Bookmark   June 19, 2011 at 10:34AM
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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..

    Bookmark   July 27, 2012 at 9:24PM
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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.

    Bookmark   September 8, 2012 at 7:11PM
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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?

    Bookmark   September 17, 2012 at 6:15PM
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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.

    Bookmark   September 18, 2012 at 11:26AM
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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.

    Bookmark   September 19, 2012 at 1:52PM
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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.

    Bookmark   July 3, 2013 at 1:18PM
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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...

    Bookmark   July 3, 2013 at 2:32PM
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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.

    Bookmark   June 13, 2014 at 11:33AM
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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.

    Bookmark   June 15, 2014 at 12:18PM
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