Troubleshooting Guide: When Thermostat Blinks “Cool On”

When a thermostat blinks “cool on,” it typically indicates that the air conditioning system is starting up and preparing to provide cool air. This is a safety delaying measure that protects the compressor and prevents the unit from short cycling. However, if the blinking continues for an extended period, there might be an issue with the thermostat or the AC unit.

Checking the Thermostat Settings

  1. Verify Thermostat Mode: Ensure that the thermostat is set to the “Cool” mode and the cooling set point is below the current room temperature reading.
  2. Inspect Thermostat Display: If the “Cool On” or snowflake icons are flashing, the thermostat might be in a delay mode, which can last up to 5 minutes to protect the equipment from short cycling.
  3. Check Thermostat Batteries: If the thermostat has low batteries, it might have trouble commanding the AC to turn on and off, which can trigger the flashing “Cool On” message.
  4. Verify Thermostat Wiring: Remove the thermostat faceplate and ensure that the wires are firmly connected to the correct terminals. Check for any loose, damaged, or miswired connections.
  5. Test Thermostat Functionality: Use a multimeter to test the thermostat’s ability to send the correct voltage and signals to the HVAC system. Refer to the thermostat’s technical specifications and wiring diagram for the appropriate testing procedures.

Examining the Furnace and Power Supply

when thermostat blinks cool onImage source: Wikimedia

  1. Inspect Furnace Door and Power Switch: Make sure the furnace door is securely closed, and the furnace’s power switch is set to the “On” position.
  2. Check Furnace Circuit Breakers: Ensure that the furnace circuit breaker switches are in the “On” position and have not tripped.
  3. Verify Indoor and Outdoor Power Supplies: Ensure that both the indoor and outdoor units of the AC system have power supplies and that there are no blown-out fuses or unusual noises.
  4. Test Voltage and Amperage: Use a multimeter to measure the voltage and amperage at the indoor and outdoor units, ensuring they match the specifications provided by the manufacturer.
  5. Inspect Electrical Connections: Check for any loose, damaged, or corroded electrical connections at the furnace, indoor unit, and outdoor unit.

Maintaining the Air Conditioning System

  1. Replace Air Filter: Dirty and clogged air filters can restrict airflow, causing the thermostat to say “Cool On” but not produce cool air. Replace the air filter according to the manufacturer’s recommendations.
  2. Clean Evaporator and Condenser Coils: Dirty coils can prevent the system from effectively absorbing and dissipating heat, disrupting the entire cooling process. Use a coil cleaner and a soft-bristle brush to clean the coils.
  3. Check Refrigerant Levels: Low refrigerant levels can cause the system to work harder, leading to the “Cool On” blinking. Have a professional HVAC technician check and, if necessary, recharge the refrigerant.
  4. Inspect Ductwork: Ensure that the ductwork is properly sealed and insulated to prevent air leaks, which can affect the system’s efficiency and performance.
  5. Clean Condenser Unit: Remove any debris, leaves, or obstructions around the outdoor condenser unit to ensure proper airflow and heat dissipation.

Consulting a Professional HVAC Technician

If the troubleshooting steps above do not resolve the issue, it is recommended to consult a professional HVAC contractor for further assistance. They can perform a comprehensive system diagnosis, identify the root cause, and provide the necessary repairs or maintenance to restore proper cooling operation.

Remember, working with HVAC systems can be dangerous, and it is essential to follow all safety precautions and manufacturer’s instructions when attempting any DIY troubleshooting or maintenance. If you are not comfortable or confident in your abilities, it is always best to seek the help of a qualified HVAC professional.