HVAC is not shutting off once the set temperature is reached (Dallas: home, home inspector)

[CDallas]

Dear HVAC experts,

The AC system in the home is one year old. The issue is the thermostat is not shutting off at night and keeps on running at the set temperature 72 degrees for long 1-2 hours.

This is the history- The AC installation company installed ducts wrongly in Master bed, laundry and master bath thereby supply duct was the return and return duct was the supply. Recently we had identified this in the 1-year warranty inspection by a third party. The AC company cut the duct at the attic and reversed the duct. After that that we observed this behavior. We see sometimes indoor fan runs intermittently, but thermostat doesn't show the fan is running.

once we set the temperature to 72/71 r. we see that temperature dropped to 72 and system keep on running for 2 hours and doesn't shut off. Sometimes it shuts off, but it won't last for a minute and then keep on running. The volume of air in the master bedroom is extremely high and we can't bear it if the machine runs for a long time.

When contacted the AC company, they said my PH is incorrect, the wall has got a higher temperature causing this. We don't know whether the AC company is correct or wrong, but what we are observing is that after the AC duct switch all these issues are happening. The AC company is always trying to prove that they are right though, But we are suffering.

Kindly advice what needs to be done in this case and what would be the potential reasons causing this issue.

Thank you, everyone, for reading the thread. Looking forward your valuable suggestions.

Regards
DP

[oldoak2000]

So, you were perfectly comfortable for almost a year, then "...The AC company cut the duct at the attic and reversed the duct. After that that we observed this behavior. We see sometimes indoor fan runs intermittently, but thermostat doesn't show the fan is running..."

maybe shoulda left it the way it was.

[TheOverdog]

The issue is the thermostat is not shutting off at night and keeps on running at the set temperature 72 degrees for long 1-2 hours.

I don't have enough info to really help, but unless you have a superfancy zoned AC, the thermostat is in or very close to the wall unit, so how your return ducts are setup is mostly irrelevant. Declaring the wall where the thermostat is as 'hot' may be an issue, but you can measure the temp of the wall yourself with a simple thermometer to see if your thermostat is working. If your A/C is getting the room to 72F or whatever and then continuing to run, then the 'temperature spread' between shutoff may be set wide. You should be able to adjust that on the unit itself.

If the wall where the thermostat is - is not reaching the set temperature, then you need a new duct somewhere nearby or you need to adjust it to a room you are comfortable in once it reaches the set temperature. Adjusting the shut-off temperature to the temp of the room you should also be able to from the unit.

If the unit is too loud from your masterbedroom, then you can insulate your attic more, and that should muffle the sound (if the unit is in the attic). If the condenser is right outside your bedroom window, then not much you can do about that except pay someone to move it elsewhere.

If the air is too strong coming out the vent, then you can partially close it with the louvres on the duct, or add an inline damper, or make the duct larger. If it's larger, usually the air will run quieter. You can also put on a vent dust filter. Other than that, not much you can do to restrict the airflow coming out of a vent.


If your return is your supply and your supply is your return, then it'll just suck in colder air and pump out hotter air until the temperature and humidity stabilize. Usually returns (input) are near the floor and supplies (output - I think I have that right) are on the ceiling, so it's an easy thing to figure out.

[CDallas]

Thank you, Mr. TheOverdog for the detailed explanation.Great.
I am worried on the AC never shuts off. It keeps on running at 72 for whole night. if I set at 72, It keeps on running at 71, if I set it at 71.If the AC runs like this, do you think this will affect the efficiency of the system?

I checked with a technician here and he advised that either the duct size is wrong or the AC capacity is not enough to cool the house. Do you think I should call a company to inspect this? If so do you have any recommendations on a good company to do HVAC inspections in Dallas.

Regards,
DP

[bigbear63]

Check the obvious FAN = AUTO -- do not set to ON.

Then have a 2nd AC company do a walk-thru inspection. Check some websites that give owner feedback ratings and pick a company for the 2nd opinion.

[CDallas]

Mr. Oldoak2000,
The AC is comfortable before. Now it is not after the duct switch. The company did this mess is Airtron.

[CDallas]

Mr.bigbear63,
Yes all settings are in auto mode,
Regards,
DP

[oldoak2000]

Originally Posted by CDallas

Mr. Oldoak2000,
The AC is comfortable before. Now it is not after the duct switch. The company did this mess is Airtron.

Maybe there was a reason the original company did it the origional way (to make it COMFORTABLE), due to the design of the house, etc.

Sorry it got messed up (not comfortable).


Also, a 2-Stage system (IF by any chance this is what you have) will seem to 'run all the time' ; that would be normal for that type, or any VERY high-efficiency system (does NOT run up the bill)- it runs in a very-low 'maintain' temp mode. However, working correctly it would keep all rooms comfortable.

Hope you get it resolved.

fyi, I've had good results with BERKEYS heating and air - tech was knowledgeable and very communicating.

[Rakin]

There is a fan that pulls in fresh air that may run after the system turns off. That should be your problem.

It's run time can be shortened.

[CDallas]

Hi Guys,

This is what I observed yesterday. From 78C to 72C system took 7 hours. Both thermostats were on. We put 72C at 9pm Yesterday and the system reached 72C at 3;29 am today.

This is what my observation. There is a big grill in the master bedroom to take the return air and I checked with a paper and the paper is not holding/sticking in the grill in the downstairs. But upstairs yes it holds well. Also, I don't feel any return air flowing from the other two return ducts in the downstairs. I checked this with an A4 size paper. Reached out to Airtron AC this morning and they are saying the system is perfect and humidity is the issue etc. I don't feel any use of calling Airtron again and again as if they are trying to prove me, I am wrong. Yes, the problem had noticed well under warranty period so they are responsible for fixing this.

I am doubting they messed up with return duct in the downstairs when they did the switch. Are there any legal authorities I can raise my issue? How can I prove that I have an issue?. I don't know how to hire a well qualified HVAC inspector who could look at this in detail and identify the root cause.

I can't trust the AC company, as I have called the company for air balancing before and they would have noticed the duct problem but they did not tell me. Later on, a home inspector identified the problem in a matter of seconds. So I feel something fishy.


Regards,