San Antonio · Thermostat Repair · Family-Owned Since 1996
About 1 in 5 'broken AC' calls we get in San Antonio turn out to be a $30 thermostat problem, not a $5,000 system problem. Here's how to tell which one you have, and what a proper replacement actually costs.
Typical price
$185–$450 installed
Time to fix
30–60 minutes
Urgency
Medium — system unusable or running wrong
Your thermostat is the brain of your HVAC system. It reads the temperature in your house, decides when to call for cool or heat, and sends low-voltage signals to your equipment. When it fails or loses calibration, the rest of the system acts broken even though everything else is fine.
Common failures: blank screen (dead batteries or no 24V power from the air handler), wrong temperature reading (drifted calibration or bad sensor), system won't turn off (stuck relay inside the stat), or it just locked up. A basic replacement is $185-$280. A smart thermostat (Nest, Ecobee, Honeywell T-series) installed runs $350-$450 including programming and registration.
Honest take: smart thermostats are great for households that travel a lot or have predictable schedules. For families that are home all day, they save very little vs. a programmable stat — buy one if you want the convenience, not because someone told you it'd cut your bill in half. It won't.
What it costs in San Antonio
$185–$450 installed — Basic programmable: $185–$280. Smart thermostat (Nest/Ecobee/Honeywell T-series) installed and configured: $350–$450. Our $59 diagnostic is waived when you approve the repair, so you only pay for the fix itself.
If two or more of these sound familiar, it's probably your thermostat.
Here's exactly what a Carnes and Sons tech does at your house — no mystery, no upselling.
Half the 'dead thermostat' calls we get are dead batteries or a tripped float switch on the AC drain. We check both first. If that's the fix, you only pay the service call (waived if any work is done).
We pull the stat off the wall and measure between R and C. 24V means the stat is bad. 0V means the issue is upstream — usually a tripped float switch, blown transformer, or broken thermostat wire.
If the stat reads but is inaccurate, we put a calibrated probe right next to it. More than 2°F off and it needs replacement or recalibration.
Not every system supports every thermostat. Some Carrier Infinity / Trane XV systems require a brand-matched communicating stat. Most standard 24V systems can use any modern stat. We tell you what's compatible before you buy.
We mount the new stat, wire it correctly (we re-do sloppy previous installs at no charge), configure for your equipment type (heat pump vs. AC + furnace, single-stage vs. multi-stage), and register the warranty in your name.
Get Your Thermostat Diagnosed Today
Tell us what's happening. We'll text you back in minutes — no call center, no robo-calls.
Basic programmable thermostat: $185 to $280 installed. Smart thermostat (Nest, Ecobee, Honeywell T-series): $350 to $450 installed and fully configured. Communicating thermostats for high-end Carrier/Trane systems: $500 to $750.
Depends on your lifestyle. If your house is empty 6+ hours every weekday or you travel a lot, geofencing and learning schedules can save 10-15% on cooling bills — pays for itself in 1-2 years. If you're home all the time, a $50 programmable from the hardware store does the same job. We'll give you our honest take based on your situation.
Not always. Try fresh batteries first. If that doesn't bring it back, the most common cause in San Antonio summers is a tripped float switch on the AC drain pan that cuts power to the stat as a safety. Once the drain is cleared, the stat comes back to life. That's a drain line cleaning, not a thermostat replacement.
If you have a C-wire (common wire) at your stat, often yes. If you don't, you'll either need a C-wire adapter or have to run new thermostat wire — which usually means a tech anyway. Bigger issue: about 1 in 4 DIY smart thermostat installs we get called out to fix has miswiring that's damaged the new stat or the equipment. Cost to fix that is usually more than just having us install it in the first place.
Basic programmable: 10-15 years. Smart thermostats: 5-8 years (the electronics fail sooner than the simple ones, and they're more sensitive to power surges).
Two main causes: (1) the thermostat's internal sensor or relay has failed and isn't sensing that it's reached temperature, or (2) the outdoor contactor has welded shut and is keeping the compressor running regardless of what the thermostat says. We diagnose both quickly.
Programmable: you set a schedule manually, it follows it. Smart: connects to WiFi, lets you control from your phone, learns your habits over time, geofences based on your phone's location. Both work fine — the smart one just has more features.
Most standard 24V systems work with any modern stat. Variable-speed and communicating systems (Carrier Infinity, Trane XV, Lennox iComfort) often require a brand-matched communicating thermostat to get full functionality. We always verify before swapping.
We're based in Stone Oak and roll trucks across San Antonio and the surrounding Hill Country every day.
License TACLB29435E · Family-Owned Since 1996
Cities & neighborhoods we serve
San Antonio · Stone Oak · Alamo Heights · Hollywood Park · Hill Country Village · Shavano Park · Castle Hills · Leon Valley · Helotes · Boerne · Fair Oaks Ranch · Bulverde · Timberwood Park · Garden Ridge · Schertz · Cibolo · Selma · Universal City · Live Oak · Converse · Windcrest · New Braunfels
No call center. The owner or one of his sons picks up.
(210) 600-5091