Why the engine runs hot when the ac is on on 1991 caprice especially when the car is idle at stop or parked?

The engine in a 1991 Caprice may run hot when the AC is on, especially at idle, due to increased load on the engine from the AC compressor. When the vehicle is stationary, airflow through the radiator decreases, which limits the system's ability to cool the engine. Additionally, if the cooling system is not functioning optimally—such as a failing thermostat, clogged radiator, or insufficient coolant—this can exacerbate overheating issues under these conditions. It's essential to ensure the cooling system is in good working order to prevent overheating.