Air Conditioner Problem

[sbudnick]

I have a Lennox 2 stage furnace and 2 stage air conditioner which were installed within the last year. During the day the temp is set at 76 and the unit cycles fine. At night we set the unit at 74 and the temp is reached fairly quickly but stays at 74 for hours and the unit does not shut off. The same thing happens if I set the temp to 73 i.e. the temp is reached but unit continues to operate at 73 but does not cycle. It hapeens if the temp is 90 or 78. The honeywell vision pro thermostat was replaced but no change. Everyone is perplexed. Any suggestions? Thanks

[dash]

When it continues to operate at 73*°,what is the the return versus the supply temperature?

Is it in high or low stage?

What Compressor stages,100/50 or 100/70?

[sbudnick]

Thanks for your reply:
I will have them check the supply versus return temp. Is there a way for me to determine the stage or is that something they have to do? I do here various clicks from the thermostat which I think is calling for a stage change but I am not sure the AC is responding. I think the compressor is 100/70. Thanks.

[wyounger]

Sounds pretty normal for a two-speed system to me. They should be on even more of the time than a regular system during hot weather, because they can step down to lower capacity instead of cycling on and off. In the dog days of summer, that may just end up meaning that it needs low at night and high during the day. It may hardly rest until Semptember, and there's not necessarily anything wrong with that.

I wouldn't worry unless you set the system to 74 and it's still cooling when the stat says 73, 72... etc. Good thermostats measure in tenths (or less) of a degree, and will do what it takes to maintain the set temperature precisely, even though you can't see the temperature fluctuating. If it's giving you the temperatures you ask for, though, it's probably fine.

It's reasonably likely that you will have a hard time determining when it's running on high and when it's running on low. There will be some difference in airflow at the vents, but it can be pretty subtle in many applications if you don't have a way to measure it beyond just putting your hand in front of the vent.

[sbudnick]

Thanks for the response. I understand that this provides more comfort with less temperature swing. How about energy usage? Since it runs more but at a lower stage it seems it might be a wash.

[BaldLoonie]

Sounds normal to me too. The Vision Pro holds a very accurate temp and long run periods on low are why you buy a 2 stage system anyway. dash, a Lennox would have the unloading scroll so 100/70.

[dash]

I agree with baldie and wyounger,except for the OP stating it does it at 78 or 90°outdoors.Maybe the cycles are shorter at 78 ,and as the should be.