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My AC can not reduce temperature more (outside / inside temperature difference)

My AC can not reduce temperature more (outside / inside temperature difference)

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  #1  
Old 07-06-12, 09:59 AM
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My AC can not reduce temperature more (outside / inside temperature difference)

Last week, the whether is hot ~107F. My AC is keeping running and never stop but inside house is as high as 85F, can't down more. Till midnight, the temperature goes to 77F as set, when outside is down to 88F. Is this normal or AC unit has the problem? Is there any possible damage to AC, if AC is keeping running about 10 or more hours? My AC unit was completed turn up last year by AC professional.
 
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  #2  
Old 07-06-12, 10:11 AM
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What temperature was the air coming out of the vents? This is a central air system, right?
 
  #3  
Old 07-06-12, 11:11 AM
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Your AC has problem, give us more information, like cold air temp, etc. may be we can help.
 
  #4  
Old 07-06-12, 01:31 PM
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No its fine! It will have a hard time cooling more than 20 degrees below outside temp. Its designed to run let it run.
 
  #5  
Old 07-06-12, 02:43 PM
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It's not fine if it won't keep the house at a decent temp. If a central A/C will only cool 20 degrees below outside temp my house would run at 90 degrees for 3 months of the year. Other people in AZ would have to put up with 100 degree inside temps.

I had a similar issue when I lived in VA (Hampton). Original 6 y/o A/C on home would kick on about 9-10AM on hot days and run all day but the temp would still climb til the sun went down and it started to cool off outside. Might reach set temp by 9PM or so.

I thought....maybe a thermostat issue... replaced old mechanical with a Hunter electronic(big mistake). No change....had a friend who did commercial A/C stop by...thought it was a little low on charge so added about a pound. No change. Finally called a small family company recommended by a neighbor. Came out and checked all the line pressures and temps and actually lowered the charge about 1/2 lb and then came inside to check airflow and outlet temps. As soon as he walked in he saw the problem...the 'stat.

He would have seen it earlier but I had told him the readings I was getting inside and I was the one who went inside to turn the unit on and off, because I wanted to "help". Told me to get a good Honeywell and the problem would probably go away. And he was right. In my case the house would start heating up and by the time the cheap/old stats kicked on the thermal load(?) was borderline for the unit to keep up.

Replaced the stat with a Honeywell 5/2 programmable (about $70 10 yrs ago) and set my preferences and even on the hottest days the house was right at the set temp. It would run for 15 min...off for 15 or something like that...it's been a few years.

Point is...get a good tech (mine charged $65 for a bit over an hour plus explaining the problem to me) and buy quality parts if needed.
 
  #6  
Old 07-06-12, 02:49 PM
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Don't understand why you said---- hard time to cool more than 20 degree... Our temp at southern Texas reaches 105-108 every Summer, if we can not provide our customers with AC producing 75F in room temp, we will be all out of business.
 
  #7  
Old 07-06-12, 03:13 PM
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Design temp for most of VA is 95 degrees. I'm sure that what it was sized at unless the HO ask for a different temp. Design temp for Texas I'm sure is higher. Unit is doing what it was designed for.
 
  #8  
Old 07-06-12, 03:25 PM
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Wen831, Why don't you provide us with your Delta T information so that we can tell if you have an AC related problem or a design issue. (DeltaT = cold register input air temperature - return air temperature)
 
  #9  
Old 07-09-12, 10:51 AM
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I have two units, upstairs and downstais. Upstairs unit runs well and cool fast. Downatais can not cool enough. So, there is the problem with my downstairs AC system. AC has been turned up last year. Could you tell me little more detail about the problem of stat?
 
  #10  
Old 07-09-12, 11:14 AM
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You can't just throw parts at it without answering some of the questions.

As clocert asked in post #8...what is the Delta T? (Probably THE most important question.)

What are the outside and inside temps when the A/C kicks on first time in the morning? What time does it start running?

Are you getting good airflow out of all vents?

We don't even know the size (square footage) of the house or the size of the A/C units.

Has it always been like this...or did it just start?

If it was checked last year...something could have failed. Nothing lasts forever.

If you can't answer some of these questions...I'd suggest you call the HVAC company and have a service call done.
 
  #11  
Old 07-09-12, 06:57 PM
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Not Holding Temp Setpoint

Last week, the weather is hot ~107F. My AC is keeping running and never stop but inside house is as high as 85F, can't down more. Till midnight, the temperature goes to 77F as set, when outside is down to 88F. Is this normal or AC unit has the problem? Is there any possible damage to AC, if AC is keeping running about 10 or more hours? My AC unit was completed turn up last year by AC professional.
You should have the A/C checked to see if it is delivering its nominal performance Rating.

Get a humidity gauge, for indoors, at a hardware store; we need the indoor humidity readings.

Take indoor supply & return temps; take outdoor temp & temp of discharge air from the outdoor condensing unit.
Post the data here; Just do it...that data will provide some good clues.

You ought to also have a Home Energy Efficiency Audit &, then do everything possible to reduce the heat-gain of your home.

Start the cooling earlier in the morning when it has more capacity to bring the temp & humidity down; it will have a better chance of holding lower temp set points.
 
  #12  
Old 07-10-12, 09:32 AM
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My downstaris AC unit is Train XB1000, TTB030C, 2.5Tons, 9 years old. Downstaris is ~1350 Sq feet. I tried to measure deltaT, and it looks ~3F, very low, although pressure pipe from outdoor AC is very hot and there is continuous condense water drop out from outdoor pipe. This situation (AC run whole day from 8AM till 10PM, and the room temperature can not down more) began last week.
Before call, I want to know what problem it may be.

Thanks
 
  #13  
Old 07-10-12, 05:23 PM
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With delta T at 3 degrees F, your AC is not performing well at all. Continue running your AC is not going to lower the room temperature much, but just waste the electricity. From the information we have now, it is hard to tell what the problem is. it can be many different reasons (low freon, weak air flow, dirty coil, frozen pipe, etc..) Suggest that you call a pro for help.
 
  #14  
Old 07-11-12, 07:57 AM
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When I call pro, how to describe the problem to let them solve it instead of adding some freon? How to clen evaporattor coil, does it locate at the inside unit? I think I may clen coil at the first to see the result.
 

Last edited by wen831; 07-11-12 at 08:42 AM.
  #15  
Old 07-11-12, 08:18 AM
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Provide us with all the numbers I asked for in my prior post:

Condenser Make____________Tonnage _________
& SEER Rating of the outdoor condenser ____

Return indoor air temp _____
Supply air temp nearest-
to air handler _____
Temp-split _______
Indoor relative humidity ______
-----------------
Out door air temp near condenser coil intake area ______

Outdoor condenser-
discharge air temp ______

Temp-split _______

With that accurate data I can tell you if it's performing near its Nominal Rating.
 
  #16  
Old 07-11-12, 11:27 AM
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In order for us to go one step further to find out what the problem is, we need more info from you. Please understand we are doing this over the internet, unless you can provide us with what we need, it is hard for us to do anything. So try to answer HVAC RETIRED's questions, and also we need to know the temp of the 2 copper pipes that go into the outside condenser. Hand touch those 2 pipes when AC is running, let us know if they are hot, warm, cold, how hot, how cold ...About the coil, it is in the air handler, search You Tube, you will find many videos teach you how to clean it.
 
  #17  
Old 07-16-12, 12:59 PM
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The model is Trane XB1000, TTB030C, 2.5 Tons
SEER: 10.00 (?)

Return indoor air temp is 85F
I can not measure nearst, because it is at living room or foyer, and is too high to reach. So I measured the register in MB room, the temp is 80F
Split is 5F
Humidity is ~35-40%
Humidity may be higher, because outdoor pipe drop water one drop by one drop.

Outdoor temp near intake is 95F
Please advise how to meausre outdoor condense dischrge air temp?

Outdoor two copper pipes:
Pressure pipe feeling really hot, I only can keep touch for ~5 - 8 Sec. Another pipe is warm only.
 
  #18  
Old 07-16-12, 01:26 PM
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I can see 3 things wrong here from the numbers/info you provided. Split is only 5F, should be around 16-18F, small pipe hot (should be just a little warm), large pipe warm (should be ice cold). Here is what you need to do: Check to see if the outside condenser coil is clean (when was last time it got cleaned ?), all in house filters clean ? and make sure the evaporator coil (in the air handler) is also clean. after all get cleaned, let's see if those numbers are getting better. you may still have to call a AC tech to check the freon charge, but not just add the freon, find the leak and fix it first.
 
  #19  
Old 07-16-12, 04:59 PM
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The model is Trane XB1000, TTB030C, 2.5 Tons
SEER: 10.00 (?)

Return indoor air temp is 85F
I can not measure nearest, because it is at living room or foyer, and is too high to reach. So I measured the register in MB room, the temp is 80F
"Split is 5F"
Humidity is ~35-40%
Humidity may be higher, because outdoor pipe drop water one drop by one drop.

Outdoor temp near intake is 95F
Please advise how to measure outdoor condense discharge air temp? (If the air discharges out the top you simply move the thermometer around in the air stream close to the top of the condenser; that is an important temp-number to get!)

Outdoor two copper pipes:
Pressure pipe feeling really hot, I only can keep touch for ~5 - 8 Sec. Another pipe is warm only. (Large pipe should be cold, Not warm.)
Clocert was correct in most of what he said.

I measured the register in MB room, the temp is 80F
Split is 5F Humidity is ~35-40%
Are U using a humidity gauge?
At 80F & 40% RH the indoor split should be around 18 to 22.


I'm sorry U didn't take the condenser discharge air temp; that was very important to our findings...

You need a real good Tech to do a thorough troubleshooting check of your entire A/C system...After cleaning both coils & later-on checking actual CFM airflow delivery, & getting it RIGHT, they must take Superheat & Subcooling temps to end-up with a correctly charged system.
 
  #20  
Old 07-16-12, 07:07 PM
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The large pipe is warm and the small pipe is very hot you say. My first guess was to say low freon, but the small pipe being hot dismisses that so there are 3 possibilities.
!. The condenser fan motor isnt running or it turns off periodically.
2. You are low on freon and your condenser is dirty.
3. The most likely of the 3 is that you have a blockage at the evaporator coil inside the lines. A blockage is some debris in the lineset, it would block the flow of freon going to the coil which would make the little line hot, it also would prevent freon from going to the coil, which gives you a low temp split and finally it would also make the large line warm.
 
  #21  
Old 07-16-12, 07:09 PM
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the condenser fan could be running backwards.................
 
  #22  
Old 07-17-12, 05:40 AM
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If there is a restriction in the high-side even at the metering device, the system will pump the refrigerant down into the condenser & it will have plenty of time to cool therefore the liquid line will not be hot.

Often the serviceman will add refrigerant which increases the liquid to a point where there is not room enough left to cool the hot compressor discharge gas & high-side pressures & temps can begin to considerably increase.

On a low charge without any restrictions the condenser will not be able to condense enough liquid & will empty out too fast resulting in a hot vapor saturated (small) liquid line; the compressor & discharge gas also get way too hot adding to the problem.

Also, on a low charge the E-Coil pressure can drop below the freezing point & therefore the indoor coil can ice-up & on down the suction line.

With cleaned outdoor & indoor coils with NO restrictions, along with the tested correct amount of airflow through the coil, then it should be charged using superheat temps on the suction line & subcooling temps on the small liquid line.
 
  #23  
Old 07-17-12, 10:18 AM
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1. Last year, I called pro to turn up the AC, and was told that he cleaned the coil (outdoor) and also charged for adding freon.
2. I replaced return filter two weeks ago, when I found the temperature can not get low till mid night.
3. Evaporator coil inside house never be cleaned since I moved in 8 years ago (house was built 10 years ago), I'm going to clean it. Where does coil locate and how difficult to do clean job (video shows coil should be moved out then clean) ?
4. If there is blockage inside line, how to find it? Can pro find?
5. Outdoor Condenser fan should blow air out or into? ( to make sure not run backwards)

Thanks
 
  #24  
Old 07-17-12, 11:28 AM
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A pro can find a blockags. Its an expensive fix. Sorry
 
  #25  
Old 07-17-12, 12:53 PM
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Why your AC cannot reduce indoor temperature

There could be a number of reasons – some obvious and not so obvious.
The good news is – many times it’s a easy fix.

Before you call a repairman there are a few things you can do.



The first thing you should do is check to see if your air filter is dirty and if it is, replace it and see if that helps.


The next thing to do is go outside and look at the outdoor air conditioner component.


Is the outdoor unit running?


If not, check the circuit breaker – if it’s tripped, try resetting it.


Make sure the thermostat setting is correct.


If the unit is running..
The next thing to do is inspect the unit.


Is there dirt or debris on the coil section?

If so, turn off the circuit breaker for the unit and spray down the coil with a garden hose (be careful not to bend the coil fins) until it’s clean, then turn on the breaker.


If the coil is clean, look at the copper lines that are attached to the unit – the small line is bare copper and the larger line will usually have black insulation covering it.


Do you see any ice or frost on the larger line?
 

Last edited by hvactechfw; 07-17-12 at 12:55 PM. Reason: removed link
  #26  
Old 07-18-12, 09:23 AM
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There is no any ice or frost on the larger line.
Using garden hose with water to spray outdoor coil?
 
  #27  
Old 07-18-12, 09:58 AM
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ALL power must be off when spraying the condenser coil, including the furnace power to cut power to low voltage control circuits in the condenser!

Keep the water stream straight in-line with the fins...

Let it dry out good before restarting it...
 

Last edited by HVAC RETIRED; 07-18-12 at 10:00 AM. Reason: Added Clarity...
  #28  
Old 07-18-12, 10:24 AM
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Question

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Please indicate where is vaporator coil locates?
The box looks coil locates ( I think) is blocked by copper pipes and the pipes have to dis-assemble (freon will lost) before I can reach the coil. I think I am wrong, but I can not find somewhere else, where there are bolt/screw and I could open.
 
  #29  
Old 07-18-12, 01:01 PM
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The evaporator coil is on the left in the photo where the large insulated suction-line & small copper liquid-line are located.

You don't have to disconnect the refrigerant lines; maybe U better leave that coil inspection to a licensed Tech. A competent Tech will check the pressure drop across the coil to see if it is normal too high, indicating there is blockage.

It could yet need cleaning if fins are insulated...
 
  #30  
Old 07-20-12, 09:25 AM
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When AC running, there is wind blowed out from two holes where suction line and liquid line installed as shown in picture. Is it normal?
 
  #31  
Old 07-20-12, 09:31 AM
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Yeah normal. It is normal.
 
  #32  
Old 07-26-12, 05:15 AM
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Replaced filter and cleaned coil, AC looks running better, at least outdoor larger copper pipe is cold (but it is not cold enough, before it is warm) and smaller pipe is warm (before it is hot). The temperature reduce process is still very slowly, almost 1 degree / 45 minutes. Maybe it is time to call pro. How to describe such situation and what pro should check?
 
  #33  
Old 07-26-12, 08:31 AM
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Time for some simple temperature data analysis...
Performance Data Collection – Best Time to collect data is Late afternoon around 4:30 pm, when attic is HOT; also when outdoor temps are around 85; 95; 105F or, anywhere in between.
*All U need is a good thermometer (digital reading in tenths preferable) & and indoor Humidity Gauge

1) Helpful; Tonnage & SEER of Unit & outdoor condenser model number: __________________

2) TXV or, orifice metering device? _______. Only if U know…

3) Outdoor condenser’s discharge-air-temperature ______-F
Subtract Outdoor air temperature: _______
Outdoor Condenser Air-Temp-Split _______

4) Need the ‘Indoor’ percent of relative humidity - away from Supply-Air outlets ______

5) Indoor Return-Air Temperature ______
Subtract Indoor Supply-Air Temperature ______ -F
Indoor temperature-split _______-F

Need the above information for troubleshooting & performance analysis.

Example below:
A Goodman 2-Ton 13-SEER condenser, 800-cfm indoor airflow; 80-F indoor dry bulb & 50% relative humidity; Indoor temp-split 18 to 19-F.
@ 85-F outdoors; 103.9-F - 85-F outdoors or around an 18.9-F temp-split;
@ Indoor 75-F & 50% RH condenser temp-split is only around 14.9-F.
You'll be surprised what clues can be revealed by the above data...
 
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