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New A/C not cooling well

Posted by praetor (My Page) on
Wed, Jul 18, 12 at 1:16

I just had the following Trane XV95/XR15 setup installed last week:

Condenser 4TTR5024E1
Coil 4TXCB031BC3
Furnace AUH2B060A9V3

The handwritten quote from the installer says its a 2 ton condenser and 2.5 ton coil but I haven't found anything to back that up.

My issue is that the system isn't keeping the house cool. I set the thermostat to 78 while I'm at work and 70 at 5pm when I get home, and today the house was at 77 when I returned at 5, then went down to 76 until my wife made dinner which caused it to go back up to 77. The temp at midnight is 73 and the condenser has been running non stop. Outside temps were 96 at 5pm and 77 at midnight.

The only time the temp setpoint is reached is sometime after midnight and prior to about 7am.

I put a thermometer on top of one of the vents and it read about 12-13 degrees lower than the thermostat. I read that this is ideally 20 degrees, is that correct?
I know I could use more insulation in the attic, however my 30+ year old montgomery ward system could keep the house at a constant 68 with no issues so I'm thinking the new unit has an issue or that it may be too small.

House is a split level with 1050 sq.ft. on the main level in central Illinois.

Any advice? Would I be justified in asking the installer to come back and take a look? If so, is there anything i should mention to them?

Thanks in advance!


Follow-Up Postings:

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RE: New A/C not cooling well

A 2 ton condenser should be able to cool a 1050 sq. ft. house. Did you tell the contractor you want to be able to cool the house down to 68-70 degrees? This is below the usual design temperature. It will be difficult to reach these temperatures when it 96 degrees outside. The capacity of your old system may have been larger. The model numbers of the condenser and coil indicate the correct sizes.

The temperature coming out of the vents should be lower. The AC is struggling to reach 76 degrees. You should call the installer and have him review the installation.


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RE: New A/C not cooling well

How well is your house insulated? Your a/c is not like a gas furnace (with vast capacity). It does not have the ability to bring your house down from 78 to 70 in one hour. Especially when its 96 outside.

Was your old A/C able to do this?

13 degree temperature lower than indoor temperature is low though, especially if its been running a while. That would mean that if its 78 inside the house your a/c would only be blowing 65 degree air. That is worth mentioning to the installer.


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RE: New A/C not cooling well

Thanks for the advice. I called the installer and he blew me off, saying it was hot out (set a record yesterday) and giving all sorts of excuses as to why it isn't working well.

I informed him that my old unit could do just fine in similar temperatures and only then did he suggest that I wait a few days and call back if it is still a problem.

I wrote the following info down last night:

Time: 8:30 pm
Outside temp: 87
Inside temp: 75

Air temp at hottest return: 77
Air temp at coldest vent: 64
(13 degree drop)

I also adjusted the thermostat to keep the house at 70 all day rather than let it rise when i'm not home and it seemed to help but i'm wasting energy by doing so.

I informed the installer about the 13 degree drop and he said the 15-20 range needed to be taken immediately before and after the coil which is contrary to what i have read. Is this accurate?

He also said that I can't let the temperature drop when I'm at work or it will never recover.. again this seems contrary to things i have read, and the factory energystar settings on my IAQ thermostat. I guess it makes sense for days when it isn't quite so hot out.


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RE: New A/C not cooling well

I run a heating and air conditioning company and if I get a call from a client who has a problem with something I installed, I respond immediately.

I would INSIST the contractor return to your home to address this problem.

Tell him you are not happy with the performance.

Ask him if he commissioned the system per manufacturers specifications...

Check air flow - should be 800 CFM (cubic feet per minute)

Check refrigerant charge using sub cooling method - the contractor should show you the results of this simple test

Temperature drop test.

Even though the system seems to be sized properly there are some cases where a home that size could have no insulation or degraded fiberglass (I've seen this happen).

Did the contractor inspect the insulation and do a Manual J heat loss/gain calculation?

Did they ask you how cool you like to keep your house during the summer? Most of my clients prefer the 72 -75 degree range.

If he did, ask to see the report.

Is the fan drawing in warm return air? If so, this is usually a leak in the return air duct

Assuming you paid the contractor in full, you are entitled to a system that should work - there is no reason for the contractor not to respond.

37 year veteran HVAC contractor

Here is a link that might be useful: 9 facts you should know about installing central air


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RE: New A/C not cooling well

What is your supply temp at several different registers during the hottest point of the day? What is your return temp? What is outside temp? What is thermostat setting? Even with average insulation properties, your unit should be able to handle conditions easily and probably cycle on and off. Your problem suggests install issue and a poor refrigerant charge should be eliminated as the top suspect.

IMO


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RE: New A/C not cooling well

MY first impression is a leak in the return duct drawing hot air in from the attic. Try running with fan only. You should get a little rise with fan only. If you get a BIG rise you probably have a return leak. This guy should not be blowing you off.


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RE: New A/C not cooling well

Is the new thermostat in the same location as the old thermostat? If this has been changed, that might make the temperature settings and readings be a bit different, especially in a spit level.


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RE: New A/C not cooling well

Thanks for replying everyone.

On Friday I bought an in/out thermometer and installed the outdoor transmitter inside the return, and set the display on top of the nearest register about 4 feet above the coil.

The best differential I have gotten is about 13 degrees late at night, averaging 10-12 during the day. The return temp is the same as the reading on the thermostat so I dont think it is a return leak.

The other new development -- and I believe this is the smoking gun -- is that the high pressure coolant line is cool to the touch. I distinctly remember that it almost burned me when the old unit was installed so Im thinking it needs freon or the compressor isn't working.

I'm going to call the installer in the morning to have everything checked out. What do I need to see from him to ensure everything is good? Some kind of report? Is seeing a differential of 20 degrees enough?

Also, should I be concerned that the compressor might be damaged due to running low on freon for a week and a half?


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RE: New A/C not cooling well

20 degrees is probably the max you will see and that would be good. I believe the system is designed to shut down once the pressures get to low..should not be any damage. Might be a leak which if he has the proper equipment he should be able to detect. MY leak was at a fitting at the evaporater coil in the air handler.


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RE: New A/C not cooling well

So a technician was out this morning and added "about 2 ounces" of refridgerant. We measured an 18 degree drop across the coil and before I left for work I measured about 15 degrees between the return and a vent.

I'm crossing my fingers that this solved the problem but these guys cut so many corners that I'm having a hard time trusting them. I took the subcooling data from the owner's manual out to the guy while he was adding refridgerant and he wasn't interested in reading it. I asked what the subcooling temperature was, and the temperature of the liquid line and tried to compare it to the gauge, and it looked pretty close, but he said that he was "substituting" or some similar term to "92". I have no idea what that means but he seemed pretty sure of it.

I ran the furnace for 15 minutes before he got there to get the house up to 75, and the A/C had only been running about 10 minutes when he added the refridgerant.

I guess if this doesn't work I'll call back and have them out in the afternoon? How important is it that they follow the subcooling instructions? Is it an exact science or is there some wiggle room?


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RE: New A/C not cooling well

Did he check to see if the air flow was at least 800 CFM?

Pressure and temperature readings get skewed if the air flow is too low.

They should also take wet bulb temperature readings.

Once the dry bulb, wet bulb and air flow readings are recorded
they will tell you what the actual output of the system is.

See my previous post also.

37 year HVAC veteran

Here is a link that might be useful: Heating, Ventilation and Air Conditioning Help and Advice


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RE: New A/C not cooling well

Nope he didn't check anything other than a couple of quick temperature readings. I'd say he was in and out in about 15 minutes.

I set the CFM myself before he came over. They had left it at factory setting (400CFM/ton/3 ton/1200CFM total) at the initial install, and as i was correcting wiring (hooking up 2nd stage heat, humidifier, dehumidify) I checked the dip switches and set it for 800CFM. I couldn't get comfortable on this setting so I set it back to 1200 for a while, but humidity was too high so now its back to 800CFM.

I'm finding out that these guys cut a LOT of corners. When they came for the initial quote the guy spent about 10 minutes in the basement and outside looking at the furnace, then took a rough measurement of the foundation and went to his truck for about 5-10 additional minutes.

I reviewed the quote and he had checked a box "yes" that asked if the ductwork was sized for 400CFM, and had written in some figures for Manual J heat/cooling loads. I understand that it is impossible for him to have calculated these figures in the time he spent in my home. He did not look in the attic and didn't ask about the windows, etc. Also did not measure ductwork or count number of vents.

After the visit a few days ago temps have been slightly better, however yesterday with a peak temp of 100 measured by my IAQ's outdoor sensor the best the system could do was 77 degrees.

I'm going to see how everything does over the weekend where temps should be in the high 80s and if it can't hold a reasonable temperature im going to stop being so polite with these guys.

Also, I went through Lowes, and the guy from Lowes was present when the quote was written so he had to have known corners were being cut.

Overall I'd say this is by far the worst $6k I have ever spent, and I really wish i could just get my old system back.


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