Having a thermostat suddenly go blank and your air conditioner stop working can be worrying and frustrating, especially during hot weather. A blank thermostat display usually indicates there’s an issue with the power supply to your HVAC system. Fortunately, there are several things you can try yourself to get your AC back up and running. In this troubleshooting guide, I’ll walk you through the common causes of a blank thermostat screen and AC failure along with steps to diagnose and fix the problem.
What Causes a Blank Thermostat Screen?
There are a few possible causes for a thermostat with a blank screen:
The most obvious cause is a power outage in your home. Check whether the lights or other appliances are working. If you’ve lost power, check your home’s electrical panel for any tripped breakers. Reset any tripped breakers and see if power is restored.
Many thermostats have a fuse located inside the thermostat itself. A power surge or electrical fault can blow this fuse, causing the display to go blank. Turn off power to the HVAC system, take the thermostat off the wall, and check for a blown fuse. Replace it with an equivalent fuse if needed.
Loose Wiring Connection
Faulty wiring is another common source of thermostat failure. Vibrations over time can loosen wire connections to the thermostat or at the HVAC control board. Check for any loose wiring connections and tighten or remake them as needed. Pay particular attention to the common wire (usually blue) connection.
If you have a battery-powered smart thermostat, depleted batteries could be the issue. Replace the thermostat batteries with new ones and see if the display comes back on. Low batteries will also cause erratic operation.
In some cases, the thermostat itself malfunctions and the display stops working. Try resetting the thermostat by removing it from the wall, waiting 20-30 seconds, then reinstalling it. If the display remains blank, the thermostat likely needs professional repair or replacement.
Why Does My AC Not Turn On if the Thermostat is Blank?
If your thermostat screen is blank, any cooling or heating system connected to it will not receive signals to turn on as expected. This is why your AC won’t activate if the thermostat fails. The thermostat acts as the brains of your HVAC system, so when it loses power or has technical problems, it can’t send electrical signals to start your air handler or condenser.
Once you restore power and fix any wiring or fuse issues that caused the blank screen, normal thermostat operation and AC functioning should resume. Just make sure to reset the thermostat programming if needed.
Step-by-Step Diagnosis and Repair
Below are detailed steps for troubleshooting and fixing a blank thermostat screen and non-working AC system:
1. Check the thermostat settings
- Make sure the thermostat mode is set to “Cool” and the temperature is lowered below the current room temperature.
- Verify the thermostat fan switch is set to “Auto.”
- Check if any holds or schedule overrides are accidentally suppressing normal operation.
2. Confirm the power supply
- Verify the wall switch controlling your HVAC system is turned ON.
- Check circuit breakers and fuses for the HVAC system and make sure none have tripped.
- For smart thermostats, replace any low batteries.
3. Inspect electrical connections
- Remove the thermostat faceplate and check wire connections. Resecure any loose wires.
- Verify the common wire is properly connected. This provides power to the thermostat.
- Look for burn marks or damaged wires and replace if needed.
4. Test component power
- Use a multimeter to check for 24-30 VAC at the control board between common and power leads when calling for cooling. If not present, problem is upstream.
- Check for power at the transformer, blower motor, contactor coils, and main circuit board.
5. Evaluate thermostat condition
- Reset the thermostat by removing it from the wall for 30 seconds, then reinstalling. See if the display comes on.
- Inspect for physical damage or buttons/screen not functioning properly. This indicates replacement is needed.
6. Check condenser operation
- Head outside and confirm condenser fan spins freely.
- Listen for the compressor making humming noises trying to start up. No sounds indicate possible seized compressor.
7. Call an HVAC technician
- If you’ve checked everything above and AC still doesn’t operate, call an HVAC professional. Thermostat wiring issues, low refrigerant, bad components, or faulty control boards can all prevent proper functioning.
Following this troubleshooting guide should help you get to the bottom of your thermostat and AC problems. Be sure to stay safe and turn off all power to the HVAC system before doing any electrical work. Most thermostat or AC malfunctions can be resolved yourself, but don’t hesitate to enlist professional assistance if needed, especially for refrigerant system or compressor complications.
Why Choose a Professional HVAC Technician?
While the steps above can help you troubleshoot basic issues, an experienced HVAC technician has the skills to fully diagnose complex thermostat and AC problems. Here are some key reasons to have a professional service your system:
- Advanced testing equipment – Pro HVAC techs use tools like voltmeters, combustion analyzers, and pressure gauges to accurately test components and verify the refrigerant charge.
- Proper refrigerant handling – Technicians are certified to legally handle refrigerant. Attempting DIY repairs on the sealed AC system can be difficult and risky.
- Electrical expertise – HVAC pros have specialized training in high voltage circuitry, transformers, and other complex electrical parts found in HVAC equipment.
- Problem identification skills – With years of hands-on experience, technicians can expertly locate issues and explain how to properly repair your system.
- Code compliance – A professional will ensure any thermostat or AC repairs meet local and national electrical codes and standards for safety.
- Warranty support – HVAC company technicians can often provide full manufacturer warranty coverage on parts and repairs they perform.
- Time savings – A technician can troubleshoot issues much faster than attempting trial-and-error DIY repairs on your own.
When your thermostat goes blank and AC fails, don’t waste time with a faulty DIY diagnosis. Call in a local HVAC technician right away so you can get reliable, lasting repairs and cool comfort restored to your home.
Preventing Future AC and Thermostat Problems
To help minimize the chances of having to troubleshoot thermostat and AC issues in the future, here are some tips:
- Use a surge protector – Connect your HVAC system to a whole home surge protector to guard against power spikes.
- Upgrade old wiring – If the thermostat wiring is over 20 years old, consider upgrading it to provide more stable power.
- Change HVAC filters – Dirty filters make your system work harder and can cause components to overheat and malfunction.
- Clean condenser coils – Use a hose and sprayer to wash debris off the outdoor AC condenser coils.
- Trim foliage – Keep plants, bushes and tree branches cut back at least 2 feet from condensing units and heat pumps. This allows proper airflow.
- Schedule seasonal maintenance – Have an HVAC technician perform preventative maintenance to keep your entire system running efficiently.
- Monitor air ducts – Check ductwork for detached sections or leaks, especially if you notice higher utility bills.
- Install a smart thermostat – Newer thermostats have power backup and wireless access features that improve reliability.
With proper preventative maintenance and care, you can avoid many common HVAC headaches. But if your thermostat does go blank someday, use this guide to get the issue resolved quickly and restore comfortable temperatures in your home.
Frequently Asked Questions
Q: Why does my thermostat periodically go blank?
A: Temporary blank screens can be caused by power surges and glitches. Install a whole home surge protector to regulate power to the system. If it happens frequently, it likely indicates loose wiring connections.
Q: My outdoor AC unit won’t start even though the thermostat is on. What should I check?
A: Verify the outdoor disconnect switch is turned on and no fuses/breakers are tripped. Then check the contactor and start/run capacitors on the condenser unit. One of those starting components may need replacement.
Q: I changed batteries in my smart thermostat but it’s still blank. Now what?
A: Most smart thermostats require a common wire (C wire) connection to continuously power the thermostat. If that common wire is missing, disconnected, or loose, the display will go blank even with new batteries.
Q: Why does my thermostat keep turning blank when I run the AC?
A: If high amperage draw when the AC compressor starts causes your thermostat to lose power briefly, the voltage may be dropping too low. This can be due to insufficient wire gauge or long wire runs. Upgrading wiring can help.
Q: Can I temporarily bypass my thermostat to test my AC?
A: You should never bypass safety devices. But you can test the condenser unit by using the fan switch on the control board or jumpering the test pins to engage the contactor manually. Only do this briefly to avoid equipment damage.
I hope this comprehensive troubleshooting guide gives you a detailed action plan to diagnose and repair blank thermostat problems that also cause air conditioning failures. Let me know if you have any other HVAC questions!