What is the reason for no air in car air conditioning gears 1, 2, 3 but air in gear 4?
2 Answers
123 gears not blowing air while only gear 4 blows air is due to the blower speed control resistor. If there is no cooling, it is necessary to check whether the air conditioning refrigerant is sufficient and whether the air conditioning pump can work normally. The blower resistor is damaged, causing the blower to only have gear 4 without gears 1, 2, and 3. Damage to the blower switch can also cause this fault. Extended information: The air conditioning blower gear 4 is the direct gear, while gears 1, 2, and 3 are controlled by the blower resistor. It is recommended to first check the wiring harness between the blower switch and the blower resistor for any short circuits. If there is a short circuit, it is recommended to address it. If the wiring harness is checked and there is no short circuit, then replace the blower resistor. No cooling is due to the air conditioning lacking electricity, and adding some refrigerant can solve the problem.
As an experienced driver, I've encountered this issue before: the AC has no airflow at low settings but works fine at the highest speed (4th gear). Most of the time, it's caused by a faulty blower motor resistor. The resistor is responsible for regulating the fan speed at settings 1, 2, and 3—just like how water slows down when passing through a valve. Once it burns out or the wiring corrodes and breaks, the low-speed settings will completely lose airflow. However, the 4th gear is different because the current flows directly to the blower motor, so it can still blow air strongly. Fixing it isn’t difficult—just take it to a repair shop and replace the resistor module. For routine maintenance, make sure leaves and dust don’t clog the AC intake vents, as poor heat dissipation can easily cause the resistor to burn out. Additionally, unstable voltage may also damage the resistor, so it's worth checking the battery and alternator.
