Why does the car air conditioner sometimes blow cold and sometimes not?

[LeFinley]

Reasons why the car air conditioner sometimes blows cold and sometimes not: 1. Excessive refrigerant. When the car is driving at high speed, the rotation speed is fast and the pressure of the refrigeration system is high. The pressure controller activates, causing the compressor to stop, and the air conditioning refrigeration stops. When the car is driving at low speed, the rotation speed is slow, the pressure of the refrigeration system is low, the pressure switch closes, the compressor works, and the refrigeration resumes, resulting in intermittent cooling. 2. Lack of Freon, and there is a leak in the pipeline of the air conditioning system. 3. The filter screen is too dirty. You can try to find the bypass valve on the filter base of the filter screen. When the pressure difference on both sides of the valve reaches a certain value, it can be opened. Generally, the engine oil flows into the main pipeline through this pipe. Use a car-specific lubricant to lubricate other related components, and the situation will improve.

[DeTanner]

I've been driving for over a decade and encountered many unstable air conditioning issues. The most common problems are insufficient refrigerant or leaks, leading to low pressure where the compressor works intermittently (cold when running, hot when stopped). Another frequent issue is damaged compressor clutch - when worn or aged, it causes poor contact and may disconnect during high temperatures or low speeds. Also, a clogged filter reducing airflow can affect cooling performance. I suggest first checking your cabin air filter - replace if dirty. Then listen to the compressor startup sound; clicking noises may indicate problems. Regular maintenance is crucial - recharge refrigerant every 2-3 years and clean the condenser. Don't ignore these minor faults as summer driving becomes unbearable. Get timely repairs to avoid costly compressor replacement later.

[Lindsey]

That old car of mine is just like this - the AC blows cold air one moment and just natural wind the next, which is so annoying in summer! From my personal experience, it's usually the electromagnetic clutch of the compressor acting up. When the contacts oxidize, it doesn't work properly and tends to disengage especially during traffic jams. It could also be poor contact in the wiring system, with wires aging from exposure to wind and rain. You can first check the fuse box to make sure nothing's blown; if that doesn't help, you'll need to open it up to inspect the relay. Oh, and a dirty cabin air filter can also affect performance - replacing it will make a noticeable difference. The repair isn't expensive, around 200-300 yuan should cover it, but it's better to go to a professional shop rather than tough it out - safety first!

[VonHayden]

Occasional lack of cold air from the AC is mostly caused by faults in the temperature control sensor or refrigeration cycle system. Inaccurate temperature sensing by the sensor leads to frequent compressor cycling; or slight gas leakage in the system causes pressure fluctuations affecting cooling consistency. A stuck expansion valve can also result in unstable refrigerant flow. During diagnosis, use a pressure gauge to measure the high and low pressure ends—abnormal fluctuations exceeding the standard range indicate repair is needed. A simple fix is cleaning the evaporator to improve heat exchange efficiency. Timely repairs can prevent more severe damage and save costs.