The answer to 'why is my thermostat not cooling' is that there could be several common causes, such as a problem with the thermostat itself, issues with the HVAC system, or issues with the power supply. Symptoms may include the air conditioner not turning on, warm air blowing from the vents, or the system cycling on and off frequently.
Some potential solutions include checking the thermostat batteries, ensuring the thermostat is set to 'cool' mode, and making sure the HVAC system has power. However, more complex issues like a refrigerant leak or a problem with the compressor may require the attention of a professional HVAC technician.