What Causes the Low-Pressure Pipe of a Car Air Conditioner to Become Hot to the Touch?
3 Answers
Causes for the low-pressure pipe of a car air conditioner becoming hot to the touch include compressor or expansion valve failure, evaporator blockage, insufficient refrigerant flow, or excessive pipeline pressure, as well as excessive buildup of dirt in the condenser copper pipes. Under normal circumstances, the low-pressure pipe of a car air conditioner should be cool, while the high-pressure pipe should be hot. If the low-pressure pipe becomes hot, the air conditioning cooling effect will be poor. More details are as follows: 1. Compressor or expansion valve failure can cause the low-pressure pipe of a car air conditioner to become hot to the touch. The air conditioning compressor plays a role in compressing and driving the refrigerant in the air conditioning refrigerant circuit. The air conditioning compressor extracts the refrigerant from the low-pressure area, compresses it, and sends it to the high-pressure area for cooling and condensation, releasing heat into the air through the radiator. The refrigerant also changes from a gaseous state to a liquid state, with an increase in pressure. 2. When the expansion valve is blocked and the air conditioner is not working, check if the refrigerant is sufficient. If it is insufficient, evacuate the system and add refrigerant, then use a pressure gauge to check if the pressure in the high and low-pressure pipelines is normal. 3. To distinguish between the high and low-pressure pipes of a car air conditioner, the thin one is the high-pressure intake pipe, and the thick one is the low-pressure pipe. You can also identify them by the letters next to the compressor connection. Some compressors are marked with S or D to distinguish them, where S stands for the low-pressure connection and D stands for the high-pressure connection.
After driving for so many years, I've encountered situations where the low-pressure AC line becomes too hot to touch, usually due to insufficient refrigerant or leaks. In the AC system, the refrigerant should cool and evaporate in the low-pressure line, but if there's not enough, the pressure imbalance causes the line to overheat. This could be due to aging pipes developing cracks or not having added Freon for a long time. Once the line gets hot, the AC stops blowing cold air, and in severe cases, the compressor might even burn out. I recommend first checking the pipes for oil stains, as that's often a sign of leakage; then quickly visit a repair shop to test the refrigerant level and top it up if needed. Never attempt DIY repairs, as you might worsen the leak. Regular AC maintenance can prevent such issues, like an annual check-up before summer, avoiding the misery of breaking down on the highway in scorching heat.
Yesterday while driving, I noticed the A/C low-pressure pipe was scalding hot. After some thought, I figured it's most likely a compressor issue. The compressor is supposed to separate high and low-pressure zones, but if internal components are worn or stuck, causing mixing between the two sides, the pipes will heat up. Sometimes, a non-functioning fan can also lead to poor heat dissipation, with engine bay temperatures exacerbating the heating. When encountering this situation, I immediately stopped to inspect – don't force it to keep running, or the compressor might completely fail, resulting in expensive repairs. Actually, it's good practice to regularly pay attention to startup sounds: unusual squeaking noises are warning signs. Getting the trouble codes checked at a reputable shop is the most worry-free approach, as it can also uncover other potential issues. Driving safety comes first – unstable A/C affects concentration, especially during hot weather when it's easy to get fatigued while driving.
