Why does the air conditioning not cool when the car is idling?

[MacHenry]

Here are the reasons why the air conditioning does not cool when idling: 1. Refrigerant leakage in the air conditioning system: Refrigerant leakage leads to insufficient refrigerant, causing the air conditioning not to cool. The solution is to add refrigerant along with fluorescent dye. After driving the vehicle for a period, use a specialized UV lamp to inspect the air conditioning system. If there are leaks, the dye will glow, allowing you to repair or replace the leaking parts. 2. Low engine speed: When the car is idling, the engine speed is low, which causes the compressor speed to also decrease. Combined with insufficient refrigerant, the instantaneous pressure boost fails to reach the standard state, resulting in excessively low high pressure and the air conditioning not cooling. Observe the sight glass on the dryer tank. If continuous bubbles appear in the sight glass during normal operation, it indicates insufficient refrigerant. If bubble flipping occurs, it means the refrigerant is severely insufficient and needs to be replenished. 3. Expansion valve damage: A damaged expansion valve prevents the system from forming high pressure before the valve, and the high-pressure refrigerant cannot reach 150 Kpa. This results in the evaporator after the expansion valve failing to cool, causing the air conditioning to not cool. Internal wear in the air conditioning compressor leads to the pressure between the compressor and the expansion valve failing to reach 150 Kpa to 200 Kpa, preventing the refrigerant from circulating normally and causing the air conditioning to not cool. If severe internal wear is found in the compressor, replacing the compressor will resolve the issue.

[McJason]

As a veteran taxi driver, I often encounter idle AC failures. When passengers complain on hot days, I first pop the hood to check if the cooling fan is scorching hot. Aging fan belts slipping or burnt motors can't maintain proper RPM, disrupting refrigerant circulation. Radiator fins clogged with willow catkins or bugs trap heat, triggering compressor shutdown as protection. Last time my car had this, hosing down the radiator instantly restored cooling. Of course, refrigerant leaks are possible—requires shop pressure tests. Worst case is seized compressors; you'll hear clunking from the engine bay. Don't push it—could fry the clutch plates!