Why is the car air conditioning not cool in outside circulation mode but cool in inside circulation mode?

[MacAriel]

Detailed explanation and solutions for the issue where the car air conditioning is not cool in outside circulation mode but cool in inside circulation mode are as follows: 1. Insufficient or too little refrigerant: If there is insufficient refrigerant in the air conditioning system, the amount of refrigerant sprayed into the evaporator from the expansion valve will also decrease. Consequently, the heat absorbed during evaporation in the evaporator will be reduced, leading to a drop in cooling capacity. Solution: Add refrigerant. 2. Excessive refrigerant: The proportion of refrigerant in the air conditioning system must meet specific requirements. If the proportion is too high, it can affect the heat dissipation, meaning more heat dissipation results in greater cooling capacity; conversely, less heat dissipation leads to reduced cooling capacity. Similarly, adding too much cooling oil during maintenance can also decrease the heat dissipation of the refrigeration system. Solution: Slowly release some refrigerant from the maintenance port on the low-pressure side of the air conditioning system.

[VanLucille]

I suspect this is mostly due to a faulty air conditioning air duct flap. Having driven for over a decade, I've encountered this issue three times—each time it was the plastic flap for the external circulation not sealing properly. Imagine this: during hot weather with external circulation on, hot air from the engine compartment mixes into the AC duct, reducing cooling efficiency by 30%. You can test it by switching between internal and external circulation while parked; if you don't hear the 'click' of the flap behind the glove box, there's an 80% chance the motor is broken. Another simple test: place a tissue over the external circulation air intake—if it doesn't move when you switch modes, that confirms it. However, newer cars now use electronic control dampers, making repairs more expensive than older models. Last time I fixed this, it cost me over 800 yuan.