The answer to 'air handler not cooling' is that there could be several common causes, including a faulty thermostat, blocked air filters, refrigerant leaks, or issues with the compressor or fan motor. Symptoms may include warm air coming from the vents, the system not turning on, or the air handler running continuously without cooling the home.
Some potential solutions include replacing the air filter, checking the thermostat settings, and inspecting the refrigerant lines for leaks. However, more complex issues like compressor or electrical problems should be diagnosed and repaired by a professional HVAC technician. It's generally best to call in an expert if you're not comfortable troubleshooting the system yourself.