Where I work has four Emerson Sensi WiFi thermostats. They allow a minimum differential between auto heat/cool setpoints of 2°F. Example, cool set at 68°F, heat set at 66°F.

The Honeywell Lyric T6 Pro (TH6220WF2006) allows you to set Auto Changeover to "Off" or "Auto". If "Auto" is selected you can set the Auto Differential between 0 and 5 degrees F. I have this thermostat and it works well though it was a bit difficult to set up the wifi the first time. Sold by Amazon, Supply House. The thermostat requires a C-wire.

Thanks so much! Most people don't want AC it's single digits outdoors but keeps my wife happy. This should help eliminate problems I encountered every season change.

I doubt it...

I did some more looking and it appears the dead band is fixed at 0 degrees with the Lyric. So it may switch modes based on time delay of some sort. They call it an algorithm.

With that said, it's not a good situation to run an air conditioner like this. That compressor has got it's work cut out for it.

Job security for me.

I understand, but a happy wife is more important than wear and tear on equipment. The unit has winter and hard start equipment installed. I also have zones controlled by an Arzel unit so it ensures some delay in switching (in addition to the condensing unit delay), especially if main house wants heat. Additionally, I set a schedule to increase the cooling trigger around 3:00 in the morning when we tend to reach the low, so I've virtually eliminated short cycles. The problem arises only at season change, though I have to change the schedule many times a year.

My HVAC installer lamented with me that we both freeze and abuse our systems to keep a happy home. He doesn't use Wi-Fi thermostats and probably has a stand-alone bedroom unit.

Note that the Lyric thermostat also has options to control the Cycle rate for each stage of heating and cooling. The Cool 1 CPH (for example) is defined as "Cycle rate limits the maximum number of times the system can cycle in a 1 hour period measured at a 50% load..." I guess this can prevent the system from turning on and off too frequently when Auto Differential is set to a low value.

QWx Explorer,

It's not that you can't do it and be successful, but normal residential systems aren't designed for the rigors of commercial type application. So if the unit in question has low temp kit installed among other things to limit adverse effects of what you are doing it can work, without too much trouble.

So what I was saying originally, was without knowing anything about your particular set up.

A long time ago I used to maintain AC equipment that would run in -40 degree below zero wind chills and 90 plus degree heat waves. But this place had 24 hour, round the clock HVAC maintenance personnel. So it can be done, when cost is no object or concern... no problem... get her done!

If you throw enough money at something... you can do anything. LOL.

QWx Explorer - if I understand, the biggest part of the problem is that the system cools down the room too much at a time close to your bedtime?

Would it work to have the cooling period (lower temperature) kick in earlier, so that it reaches the cool temperature earlier (and starts to warm up before you go to bed)? Hopefully on its next cool cycle you'd already be asleep.

Another suggestion - that may sound a bit crazy but actually work - consider a small space heater to even out the temperature. (You could get more elaborate and have a minisplit in the room but would probably be overkill.) Yes, it would be silly from a resource perspective, but if you're only using it for a half hour a day or so and it keeps you from having to get overly elaborate fiddling with the system for the whole house, and if it makes that one special person happy, why not?

The bedroom cools down perfectly and shuts off at the precise temperature. The problem is that, as the night cools sometimes 30-40 degrees outside, I no longer need cooling at all. I need the furnace to hold it at the ideal temperature-- not three degrees cooler; though one degree is probably mandatory with the most flexible thermostat. The problem IS THE THERMOSTAT. I know a manufacturer can't afford to do a lot of one-off suggestions but a good one would set defaults correctly and leave customization to the field. In this case, software controlled thermostats yield an inferior solution to prevent dumb people from doing dumb things. I prefer elegant design over inferior dumbed down design

Do you live in Napa Valley? This sounds like northern California weather where the high temperature during the day is in the low 90s, and night time drops to the low 50s.

If you have a split AC and furnace system then I don't think there is an issue in damaging equipment as long as you don't operate the AC when the outdoor temperature is below 60. It would be nice if there was a safeguard preventing that condition. The indoor furnace is not affected by outdoor temperatures.

Mike there are controls that can be used for stopping AC condenser from cycling during colder weather, just as much as low ambient kit. Deciding whether to allow AC condenser from cycling or not is mostly the application and what the goals of the structure are.

As long as the equipment is operated with proper ambient controls and the cycles are adequate to move oil thru the system, it can work just fine.

QWx Explorer,

Another option would be to add fresh air intake, when the AC is calling and low temps are activated, the system blower merely runs and draws air from fresh air intake that is controlled via a powered damper. The AC condenser isn't used typically below 55-58 degrees outdoor ambient in this type of set up.

If the application is more sensitive like data room type application, fresh air may not be used. So it really depends what the goal is of the structure.

In terms of thermostats allowing 0 degree band setting from heat to cool. It's mostly not done because of the 'play' issue. Some system designs could possibly never shut off... meaning the AC runs, temp drops the AC cycles off and heat cycle starts moments later runs a time, cycles off only to have the AC kick on again and so on.

In other words, the HVAC system would be fighting itself. The home owner gets the heating and power bill and shock and awe consume them...

If a setting on a thermostat was determined to be the cause of equipment failure, the manufacturer of the equipment could void the warranty of the equipment because they all have clauses with in warranty papers that limit their exposure to such things.

Falls under 'using unapproved' controls / improper installation of equipment etc. You might get away with it a few times... but repeated failures under a warranty is outside the realm of 'normal failure'.

The other is that the company that repairs the system when it fails offer labor warranty coverage on their dime, typically 1 year some cases as much as 3 years. So if you lose two compressors in a years time, that company that does the work is probably going to look into ways to either deny the coverage or cut you loose.