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DIY Smart Thermostat Install Goes Wrong

Google’s NEST Learning Thermostat

Every homeowner likes to be self-reliant, and for decades installing a new thermostat was simple. The rise of Digital Programmable Thermostats like Google Nest, Ecobee, and others have added complexity.

When it comes to changing thermostats there’s online sources like this one at The Home Depot and this informative post about choosing Thermostats.

You (the homeowner) are told you can easily switch out your own thermostat. Please be warned: This “simple” device is the master control for your AC and furnace. A simple mistake can potentially cost you thousands of dollars in repairs.

Here’s a reddit post of a home owner converting to a Nest, and the furnace and AC are both running. On top of not heating or cooling, it can potentially destroy the compressor. This is why home inspectors are warned to not test A/C units in temps below 60F.

Thermostat’s like the NEST can be wired for heat pumps or standard air conditioners. They can do it all! This smart, little thermostat gives you a step-by-step guide of the installation process. Typically it asks questions, and how you answer those questions determines which wires go where.

Unfortunately some homeowners don’t know the difference between a heat pump and an AC. One of my customers wired his unit for a heat pump, and naturally the thermostat told the Air Conditioner’s compressor to turn on in heating mode. For a heat pump this is correct. They have features to ensure safe operation at low temperatures. Straight AC systems only cool, and running in the winter can cause liquid refrigerant to “slug” the compressor, damaging it beyond use.

One little wire in the wrong place, or a menu item not selected right, can cause major problems.

If you have any doubts about wiring a thermostat, please call a certified HVAC pro. Paying that person a couple hundred dollars will save you money, because according to replacing an A/C compressor can cost between $1800-$2800.

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