Why does the car air conditioner sometimes blow air and sometimes not?
3 Answers
This phenomenon occurs due to the freezing of the evaporator coil. The air blown by the blower must pass through the evaporator coil to be cooled before becoming cold air. However, if a layer of ice forms on the surface of the evaporator coil, the air cannot pass through, making it seem like no air is blowing out, even though the blower is still running. There are two main reasons for the evaporator coil freezing: 1. Temperature sensor: If the temperature sensor on the evaporator coil is damaged, it cannot detect the freezing, causing the compressor to continue running and leading to ice formation. 2. Refrigerant charge: Some compressors have a variable displacement valve. If this valve fails, the compressor will not stop, resulting in freezing. If the issue arises after a recent refrigerant recharge, it could also be due to an incorrect amount of refrigerant. Before recharging, it is essential to vacuum the system and then refill it with the standard amount of refrigerant specified for the vehicle.
Having driven for over a decade, intermittent air conditioning issues are quite common. Possible causes include blower motor problems, such as unstable speed due to aging; a clogged cabin air filter obstructing airflow, resulting in sporadic vent output; or poor electrical contacts, like worn fan switch or relay contacts—toggling the switch might temporarily fix it, but recurring issues warrant inspection. Additionally, blocked AC system lines or voltage fluctuations can disrupt blower operation. DIY solutions include cleaning the filter or checking the fuse box, located in the engine bay or under the driver’s seat, but avoid deep disassembly to prevent electric shock. Regular AC maintenance, like cleaning filters, prevents major headaches. If the AC fails mid-drive, slow down and open windows for ventilation—safety first.
My car's air conditioning had the same issue before, where the airflow would intermittently stop and start, especially in summer. Possible causes include: a faulty fan itself, worn bearings, or a stuck fan leading to unstable operation; loose wiring connections, particularly at the plug, which may disconnect after bumps; or a sensitive air conditioning control system where temperature fluctuations could affect the airflow continuity. You can start by self-checking: after starting the engine, listen for changes in the blower sound—if there's no sound but it comes back after a while, it might be a connection issue. Try pressing the switch a few times. Don’t tamper with the wiring yourself; take it to a repair shop and let the mechanic test the resistance with a meter. Don’t delay fixing such a minor issue—driving without AC in hot weather is miserable. In my case, replacing the blower assembly finally solved the problem.
