Why would your Uplander throw heat while driving and cold air when idling?

Low refrigerant level: If your Uplander has low refrigerant levels, it can lead to a decrease in cooling capacity. This can cause warm air to blow from the vents when driving, as the AC system is unable to sufficiently cool the air. However, when idling, the lower engine speed reduces the demand on the AC system, allowing it to cool the air effectively and produce cold air.

Defective blend door actuator: The blend door actuator controls the mixing of hot and cold air in the HVAC system to adjust the temperature. If the blend door actuator is faulty or stuck, it may cause the system to default to heating mode, resulting in hot air blowing through the vents. When the vehicle is idling, the engine heat is lower, and the AC system may be able to overcome this issue, allowing cold air to come through.

Malfunctioning thermostat: The thermostat regulates the flow of coolant to the AC condenser. If the thermostat is stuck in the closed position, it can restrict coolant flow and reduce the cooling capacity of the AC system. This can lead to warm air blowing while driving, while idling might allow the system to cool the air effectively due to reduced heat load from the engine.

Compressor issues: A faulty or malfunctioning AC compressor can cause a lack of cooling. When driving, the increased demand on the AC system can expose the compressor's weakness, resulting in warm air. However, at idle, the compressor may still be able to provide some cooling, leading to cold air.

Cabin air filter: A clogged or dirty cabin air filter can restrict airflow and reduce the effectiveness of the AC system. This can result in warm air blowing through the vents. Replacing or cleaning the cabin air filter may resolve the issue.

It is recommended to have your vehicle inspected by a qualified mechanic or automotive technician to diagnose the exact cause and perform the necessary repairs or maintenance.