The answer to 'why is my condenser not cooling' is that there are several common causes, including a dirty air filter, low refrigerant levels, a malfunctioning compressor, or a problem with the condenser itself. Symptoms may include the unit not turning on, warm air blowing from the vents, or the system short-cycling (turning on and off rapidly).
If the air filter is dirty, replace it and see if that resolves the issue. Low refrigerant could be due to a leak, which will require a professional HVAC technician to diagnose and repair. A faulty compressor or condenser may need to be replaced entirely. It's best to call a qualified HVAC technician to properly inspect and diagnose the problem, as attempting DIY repairs on the refrigerant system or electrical components can be dangerous.