The A/C cools very well while the vehicle is moving, especially once I am driving around 40 MPH or faster. The issue mainly happens when the vehicle is stopped, parked, idling, or sitting at a red light during very hot weather.

When the outside temperature is around 99°F or higher, the front A/C may begin to lose cooling while I am sitting still. If I turn on the rear A/C at the same time, the problem becomes much more noticeable and the system may start blowing warm air.

Once I begin driving again and get some speed, the A/C starts cooling normally again and can become very cold. If I stop again and let the vehicle idle, the cooling can fade and the air can become warm again.

The issue seems to be directly related to vehicle speed, outside temperature, and the extra load from using the rear A/C. The system performs much better when airflow increases while driving.

Other Symptoms / Information:

• The A/C light has blinked before.
• A shop previously mentioned a possible “compressor locked” condition.
• A system flush was also recommended.
• The problem is much worse during extremely hot weather.
• The A/C can work normally in cooler conditions.
• The front A/C usually performs better when the rear A/C is turned off.
• While driving at highway speeds, the A/C can work like there is no problem at all.
• The issue returns mainly when the vehicle is stopped or moving slowly.

I am trying to determine whether this could be related to the compressor, condenser airflow, cooling fans, refrigerant pressures, expansion valve, rear A/C system, or another component before replacing expensive parts.