Can a Bad Thermostat Have Heat But Not Cool?

In a word, yes. If the thermostat is set to cool but the AC is not turning on, the thermostat may be to blame. A malfunctioning thermostat may be able to signal the heat to come on but fail to communicate with your air conditioner or heat pump to start cooling.

There are several reasons this can happen:

• Thermostat wiring issues
• Calibration issues
• Thermostat sensor issues
• Bad/failing thermostat

To check the wiring, you can remove the front cover/faceplate from your thermostat and look, but don’t touch, the wiring. If your home or thermostat is older, you may notice frayed wiring. You may also notice the copper end of a wire has come loose from the screw holding it down.

Frayed or faulty thermostat wiring will need to be replaced by a qualified HVAC technician or electrician. You may be able to tighten loose wiring yourself, but first you must turn off the power to the thermostat and the AC system. If you’re experiencing issues with your thermostat or HVAC system, the safest thing to do is contact your HVAC company.

Occasionally, as a thermostat ages, it can become less accurate. You or your HVAC technician may be able to recalibrate the thermostat so that it works properly to maintain a comfortable room temperature. If problems displaying and maintaining an accurate temperature persist after recalibration, it may be time to replace the thermostat.

All thermostats use sensors to detect the indoor temperature and signal your heating or air conditioning system to start heating or cooling, based on the season and your set temperature. Like any mechanical part, they can eventually go bad. This is more common in older thermostats.

Your thermostat can also accumulate dust and grime behind the cover, causing the thermostat to fail to read the indoor temperature correctly. This is another reason why regular maintenance is important. During a professional maintenance visit, the HVAC technician should check your thermostat along with the indoor and outdoor HVAC units for efficient operation. They will clean parts as needed.

While the other three issues mentioned may be able to be fixed so that your thermostat starts communicating with your HVAC system like it should, a bad or failing thermostat needs to be replaced.

Changing out a thermostat is a job best left to HVAC professionals. They have the experience to replace a thermostat quickly and easily, calibrate it, and test it to ensure it communicates with your HVAC system as it should. DIY installation can lead to its own set of problems.

We’ve mentioned an old thermostat a couple of times. In general, an HVAC thermostat is considered old when it’s 10 years old or more. Years of wear and tear may start to take their toll, and the technology has vastly improved.

If you have an older thermostat that’s causing issues, consider replacing it with a smart thermostat. They can help you easily reduce your energy usage and energy costs while increasing your comfort, especially when paired with an efficient HVAC system.

The first step is consulting with your HVAC company to find out the specifics about your HVAC system and what thermostats out there are compatible. For example, not all thermostats are heat pump thermostats.

In addition, if you have a variable speed system, you need a thermostat that can work with 700+ fan speeds for the best efficiency and comfort. Many of today’s mass-market smart thermostats can only accommodate up to two fan speeds.

Don’t spend any money until you consult with an HVAC professional. Get some tips on how to find the right thermostat for your home.

If your thermostat died or is on its last leg, now is a great time to upgrade to a smart thermostat for the biggest energy savings. Smart thermostats are programmable thermostats with extra features to help you optimize your home comfort while cutting your energy bills.

Some smart thermostats even learn your habits and come up with a heating and cooling schedule that provides optimal comfort and maximum savings. Also known as WiFi thermostats because they connect with the internet, you can control your HVAC system from anywhere, anytime, with an app.

But before you buy another brand online, learn about the advantages of Trane smart thermostats and Trane Diagnostics. It’s a monitoring service for your HVAC system where your dealer can spot small problems before they become big ones.

You can set this up through the Trane Home App. You don’t have to have a Trane HVAC system – just a Trane smart thermostat. Both the XL824 and the XR724 are compatible with most conventional 24V central HVAC, heat pump, and dual fuel systems.  

In addition, our smart thermostats have industry-leading warranties. While certain heavy hitters have a warranty of only 1-3 years, Trane smart thermostats come with a 10-year registered warranty (5 for the XR724) if thermostat installation is completed by a Trane dealer and either you or your dealer register it within 60 days of installation. Even our base limited warranty is better - generally 5 years (1 year for the XR724).

Learn about Trane’s Best Thermostats. Then schedule a consultation to learn how a thermostat upgrade can save you money on heating and cooling costs.

If your thermostat stopped working properly and your house feels like a humid rainforest, contact your local Trane dealer for help. If it’s a Trane smart thermostat and you have granted Trane Diagnostics remote access, they may be able to troubleshoot the issue and fix it remotely.

If you need a thermostat replacement or have other HVAC issues, they can also schedule an on-site visit to get your HVAC system operating as it should.

Anne Fonda, Content Writer at Trane Technologies

A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.

She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism. When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.

Expert review by Michael Morey, Smart Thermostat Product Manager

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