Home thermostat questions... (house, construction, contractor)

[loves2read]

We have three HVAC units for our 2 story house w/separate thermostats for each...all original to house's construction about 13-14 yrs ago so no Wi-Fi compatibility ones...
we have been here since late 08
We replaced the main AC unit about 8 mo ago in Dec to save some money and have had two instances where it stopped cooling already...one in June and one last week...
remember it wasn't really used until middle of April...

Both times the house had been empty for while and non-cooling was discovered when people came in so no way to tell how long it might not have been functioning. The guy added a little coolant first time (maybe because installed in Dec and was cooler outside) but could find nothing wrong this time--no charge to us either time --under warranty And seems to be working ok now...

He said if the thermostat ONLY used batteries, the batteries could be too weak to support all functions...
Like fan might come on but not compressor...so that was why there was no cooling.
Temps once working were very good...20 degree difference and 16 is acceptable...

He checked thermostat and said it was ONLY battery powered...had no wire for house power...

My husband wants to replace all three thermostats w newer ones w/wi-fi so we can monitor when away and all of them (based on what I see on Amazon) are "hard-wired" to house electricity...

Is it possible to have a fairly new HVAC system and have thermostats NOT wired to house's power?
Having to run power to new units would be good bit more expensive than just new thermostat units...

[PRND321]

Do you have C wire (24VAC common)? That's what provides power to thermostats

https://sensicomfort.com/c-wire

[maemo]

Even though your current thermostat is battery powered, you may still have a 5th common wire that is unused (usually blue in color). If unused, it's usually wrapped around the bundle. Depending on your thermostat, you can usually just snap off the front to look at the base plate with wires connected to look for the common wire.
If unused, you may need to open your furnace to check that the blue wire is connected to the furnace control board.
Not hard, but not everyone wants to crawl around a hot attic figuring how to access the furnace.

In the case you do not have a common wire, your options are really Sensi and Nest.
Sensi is battery powered and Nest draws power from your red wire to recharge it's internal battery. Both are wifi capable and can be accessed remotely via phone app or web portal.

Most standard single stage ac/heat units only need 4 wires to the thermostat (R, G, W, Y). So if that's what you put in recently, the contractor most likely just re-used your existing wiring and did not pull new a new wire bundle w/ more wires.

[Sunbather]

Originally Posted by loves2read

My husband wants to replace all three thermostats w newer ones w/wi-fi so we can monitor when away and all of them (based on what I see on Amazon) are "hard-wired" to house electricity...

I can't answer regarding wi-fi thermostats (ecobees are my favorite there, but im not sure they have a non-hardwired thermostat), but Honeywell has good wireless FocusPRO thermostats. I used 2 of them in my previous house. Battery-powered only, no hardwired power (i didn't even attach them to the wall). I had no problem with either thermostat in the 3-4 years they were in the house. Of course this is not wi-fi and cannot be accessed remotely.

[Katana49]

If your house was built 13-14 years ago (2003-2004) I find it very odd that you wouldn't have a C wire. Our last home was a 2005 and it had it, and the home was nothing special, standard builder grade.

Turn off the power to the A/C and furnace on one unit, then take the thermostat off the wall and check the wiring and see if you have any unused wires that are capped off/disconnected. Until you do that, you won't know what kinds of thermostats you can use or not.