The answer to 'furnace not cooling' is that there are several common causes, including a clogged air filter, low refrigerant levels, a problem with the compressor, or issues with the thermostat or electrical components. Symptoms may include warm air blowing from the vents, the furnace running constantly, or the unit not turning on at all.
In many cases, the solution may be as simple as replacing a dirty air filter or resetting the thermostat. However, more complex issues like refrigerant leaks or compressor failures will likely require the expertise of a professional HVAC technician. It's generally best to call for professional service if you're unsure of the cause or don't feel comfortable troubleshooting the system yourself.