# A/C not cooling to thermostat setting?



## stephgpdiy

About two weeks ago I noticed that it was getting warm in my home occasionally. especially when I ccoked and when i did laundry. The a/c was not keeping up with the setting on the thermostat. It would do it every once in awhile and then it would work regularly. Last night I noticed it happening again but this time it has not fixed itself. It stayed at a consistant 81 but had the thermostat at 76. We usually keep it at 78 and it stays on that temp so dont know whats going on? Unit is only over three years old. help!!! My husband is pretty handy but need some advice as to what we are dealing withj.


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## qbert

Start simple, is the filter clean? Is the out door unit running? Is there cool air coming out of the registers? what is the temp out doors? temp of air coming from registers?


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## Bugeyz

*Me, too!*

This is not really a reply, because I have exactly the same problem. 

This 4 ton Trane XL19i was installed November 2008. This happens only occasionally...once every two weeks or so. The AC filter is clean. When this happens the temp outsid is typically 85 to 90 degrees and humidity is above 90%. It seems to happen more in the evening (5:00 PM to about 12:00 PM). Inside seems stuck at 80, Thermostat is calling for 76 to 78. Evaporator fan is on (its hard to tell with this new system), air out of the registers is about 65 degrees (typical is 60 - 61 degrees when this is not happening). Outside condensing unit is on and removing heat.

It does not seem to matter where the thermostat is set, I have pushed it to 72 and it still sits at 80 in the house. After a few hours, the system starts working normally. I have had the AC people out and the unit checks out fine. Freon is full. 

I suspect the unit is not switching to the larger compressor in the condensing unit. Anyone have any thoughts?

Pete


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## hennyh

An A/C unit has a dual purpose. It needs to remove sensible heat (ie reduce temp) and remove latent heat (ie humidity). If you inject a bunch of humidity into the home when the temp is the highest it might struggle to keep up.

You might want to stage the humidity producing events like laundry to the cooler parts of the day.

Other then that, make sure airflow is optimal. The condenser, evaporator, filter all should be clean and not impedig any airflow. It's the same with register vents. Leave then open for maximum airflow.

If the system has taken a major turn for the worse then call in a pro. HVAC is a very challenging DIY project.


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## beenthere

Bugeyz said:


> This is not really a reply, because I have exactly the same problem.
> 
> This 4 ton Trane XL19i was installed November 2008. This happens only occasionally...once every two weeks or so. The AC filter is clean. When this happens the temp outsid is typically 85 to 90 degrees and humidity is above 90%. It seems to happen more in the evening (5:00 PM to about 12:00 PM). Inside seems stuck at 80, Thermostat is calling for 76 to 78. Evaporator fan is on (its hard to tell with this new system), air out of the registers is about 65 degrees (typical is 60 - 61 degrees when this is not happening). Outside condensing unit is on and removing heat.
> 
> It does not seem to matter where the thermostat is set, I have pushed it to 72 and it still sits at 80 in the house. After a few hours, the system starts working normally. I have had the AC people out and the unit checks out fine. Freon is full.
> 
> I suspect the unit is not switching to the larger compressor in the condensing unit. Anyone have any thoughts?
> 
> Pete


Trane 19i's come with a 2 year labor warranty from the installer.
Part of Tranes requirement to sell a 19i.

Call the installer back, its a free service call.


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## Bugeyz

Good news! 

I called the installer back. After hearing my woes, he suspected the Trane thermostat was programmed wrong. He reviewed the factory programming for the thermostat. He found out that it was only calling for the small (in my case 2 ton) compressor to come on. It never called for the larger (4 ton) compressor to come on. So I was trying to cool a 4 ton house with a 2 ton compressor. On the hot days it just couldn't maintain until the heat load was reduced in the late evening. The best it could do was about 79 or 80 degrees.

A few button pushes and he was done. The house is keeping cool. I am able to cool the house 4 degrees with ease and then the small compressor kicks in to maintain. :thumbup:


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## BelaBela

*I have the same problem - ac unit not cooling to thermostat setting*

I purchased a Carrier 25HBA that was connected to an existing Carrier furnace, installed by an HVAC professional. It simply does not cool to the wall thermostat setting with the same issue as the original writer, esp. obvious on humid days with temps over 80 degrees. The technican made repeated service calls and the condensor appears to be doing its job, but the hosue never really cools. Thoughts? Advice? Thanks


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## beenthere

Should have replaced the old indoor coil.

Call another tech that has no vested interest in it.


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## BelaBela

beenthere said:


> Should have replaced the old indoor coil.
> 
> Call another tech that has no vested interest in it.


What is an indoor coil? I have called another tech. I have also installed deflectors on the registeres. Do you think that will help?


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## beenthere

The part that sits on top of your furnace.
Installing an new condenser on an old coil. You don't get the full cooling capacity of the new unit.

Deflectors probably won't help, if the old unit cooled without them.


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## BelaBela

The old unit didn't cool properly either. Any other advice? Thanks!


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## beenthere

A load calc to see what size A/C you really need.
And a check to see how many CFMs your blower is moving(not just hold hand at register and say air flow is good)
Along with checking for air leaks in the duct system..


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