Unable to Properly control Temperature (A/C)

[Jsf721]

We installed a new central A/C unit to cover the upstairs in my home (3 Ton Reehm). The old unit was destroyed in the Hurricane. It is just getting really warm in NY and the AC is getting quite a work out.

I posted a few day ago about the issue where I cannot control the temperature properly. Some of you were good enough to suggest that I provide better detail so that I can get some advise.

I purchased an IR thermometer and here is the findings. Last night T-Stat set on 73 and the air comming from the vents was 68 degrees. This creates a cold climate before the unit kicks off. It then lets the temperature rise to 74-75 degrees before it kciks back on and make it uncomfortable cold. If I raise the temperature 1-2 degrees the unit kicks off and the space becomes stale and warm. The fan is set to auto. There is also an atic fan to pull out the warm air in the atic and crawl space.

The layout of the upstairs is posted below (not to scale -sorry):



The T-stat with was not replaced with the new unit. I was planning on replacing it but wanted to post this before doing so in case there is something else to try.

As always Thanks

 

[JakeKohl]

So far, everything sounds normal.

What is the air temperature near the thermostat when it turns off the unit?

68 degree duct exit temperature doesn't sound overly cold. Also note that an IR thermometer is not very good at measuring air temperature. Actually, it doesn't read air temperature - it only reads a surface temperature and the reading can swing wildly based on the reflectivity of the surface (teflon pans, for example, will read very low on an IR thermometer unless it's calibrated for that surface). A standard thermometer is all you need... A digital grilling/meat thermometer works well if they have the appropriate range and can be had for about $10.

 

[Jsf721]

I will pick up one of those and report back.

So far, everything sounds normal.

What is the air temperature near the thermostat when it turns off the unit?

68 degree duct exit temperature doesn't sound overly cold. Also note that an IR thermometer is not very good at measuring air temperature. Actually, it doesn't read air temperature - it only reads the surface temperature and the reading can swing wildly based on the reflectivity of the surface (teflon pans, for example, will read very low on an IR thermometer unless it's calibrated for that surface). A standard thermometer is all you need... A digital grilling/meat thermometer works well if they have the appropriate range and can be had for about $10.

 

[Falcon67]

Air coming out our vents runs 58F on a standard AC check thermometer.