Thermostat Gone Bad?

[Carbo]

One year old A/C split system. House felt warm, thermostat was at 81, temp set at 77. When the temp rose above 81 the A/C kicked on as normal, then shut off at 81. No matter what I try the temp keeps defaulting back to 81. Been happening for the past few hours. I'm convinced it's the old Honeywell RTH2300/RTH221 gone bad. But before I kick it to the curb I'm thinking maybe a factory reset will salvage it. Be damned if I can figure how to do that. Anyone? It's 90 degrees and my wife is menopausal.

 

[bbhaag]

That's a pretty old thermostat. Are you sure it is compatible with your mini split?

 

[Carbo]

It seems to be compatible. It's worked fine since the new system was installed last May. It just started acting up yesterday. I was thinking a hard reset might help but I haven't found a way to do it.

 

[Paperdoc]

I do not have that thermostat, but you could try contacting Honeywell Tech Support to ask them about this idea. On my thermostat there is a separate Installer's Menu system that most users will not access or use. It is detailed in the owner's manual, but the manual for your Honeywell unit does NOT say anything about such a menu system, so it may not exist. But maybe ....

Anyway, ONE item in the Installer Menu mine is a way to adjust the calibration of the temperature sensor. Using that you can make the temperature it displays on the front agree with the REAL temperature in the room as observed on a separate reliable thermometer. So IF you think your thermostat is NOT reading the room correctly, that is how I can "fix" mine to get it correct. However, if that 81F reading is the correct one, then this idea would not help.

Otherwise their Tech Support people nay have other ideas to help you.

 

[Carbo]

I'll be calling tech support tomorrow. Worse case, the unit's dirt nap is here and I'll replace it with a new one. By the way, I guess I'm old school. A quick glance at thermostats and I see everything is smart, wi-fi, and programmable. My preference is a simple on-off and select the temperature.

 

[PowerEngineer]

Might try replacing the batteries...

 

[BonzaiDuck]

I have a Honeywell -- not that old however.

I discovered the "Hold" button. If you change the temperature setting, it is otherwise only temporary, and will revert to that previously set. The "Hold" button seems to make your new temperature setting permanent until you go through the process again.

 

[Muse]

Bought my fridge in 2000. I've repaired it 2 times, 2021 and again the last 2 weeks. Both times the repair amounted to replacing a thermostat.

2021: The freezer temperature thermostat (I guessed right). The freezer had stopped being able to maintain the temperature range

2025: The defrost thermostat had become at best inconsistent and around 2 weeks ago stopped allowing the defrost heater to turn on.

Here's a photo of the bad defrost thermostat I replaced yesterday, note the bulging top, a tipoff that it was the culprit:

 

[WilliamM2]

Bought my fridge in 2000. I've repaired it 2 times, 2021 and again the last 2 weeks. Both times the repair amounted to replacing a thermostat.

2021: The freezer temperature thermostat (I guessed right). The freezer had stopped being able to maintain the temperature range

2025: The defrost thermostat had become at best inconsistent and around 2 weeks ago stopped allowing the defrost heater to turn on.

Here's a photo of the bad defrost thermostat I replaced yesterday, note the bulging top, a tipoff that it was the culprit:

Really common issue. Mine was bought in 2002, and the defrost thermostat failed in 2020, just like yours. Fixed for $11.
Hard to believe some just buy a new fridge.

Not sure what that has to do with an HVAC thermostat though.

 

[Muse]

Really common issue. Mine was bought in 2002, and the defrost thermostat failed in 2020, just like yours. Fixed for $11.
Hard to believe some just buy a new fridge.

Not sure what that has to do with an HVAC thermostat though.

I couldn't find one for $11. I had to pay $21.