Why is the low-pressure pipe cold but the car interior not cooling?
4 Answers
The cold low-pressure pipe indicates normal refrigeration. Check if the evaporator filter inside the car is clogged. If clogged, it will affect heat exchange at the car's evaporator, allowing hot air from the interior to escape outside. A blockage results in minimal cooling capacity, preventing the interior temperature from dropping. Also, verify if the car's air recirculation is turned off - having it on can prevent proper cooling. If these checks don't resolve the issue, inspect whether the air conditioning system's operating pressure is normal at a repair shop. Below are routine checks for non-cooling AC systems: Refrigerant check: Verify if the system has refrigerant. If not, pressurize to check for leaks before refilling. If refrigerant exists, check compressor operation. If inactive, inspect the AC pressure switch, temperature control switch, and related circuits. AC heat dissipation check: Examine the AC's heat dissipation and fan operation. Clean the condenser.
Last time I encountered a similar situation, it took me a while to figure out the problem. If the low-pressure pipe feels cold but the car isn't cooling properly, there's an 80% chance the cabin air filter is clogged like a wall. That thing is located behind the glove box, and replacing it yourself is just a matter of a few dozen bucks. If the airflow is normal, then check the temperature sensor - if that's broken, the AC thinks the cabin is cool enough and slacks off. The most annoying issue is evaporator coil frosting - the pipes look icy cold, but the cold air can't actually circulate. By the way, if you notice the AC drain tube isn't dripping water, be alert for frost buildup and immediately turn off the AC to let it thaw. Remember to regularly clean the evaporator coil, otherwise mold can clog the fins and cause bigger trouble.
Don't rush to recharge refrigerant if the A/C isn't cooling enough. Icy cold refrigerant lines indicate sufficient refrigerant levels. Focus on checking the blower system - weak fan speed prevents cold air delivery (you'll feel warm air at vents). Another culprit could be stuck air blend doors stuck on fresh air mode, pulling engine heat inside. The weirdest case I've seen was a faulty heater control valve leaking hot coolant, completely negating A/C cooling. DIY check: feel heater core pipes - if scalding hot, that's your issue. Aftermarket stereo installers: double-check blend door motor connectors; loose plugs cause unresponsive flaps.
I've fixed quite a few cases like this. When the low-pressure pipe frosts over and emits cold air but the car interior feels stuffy, there are basically three possible issues: the expansion valve is stuck at minimum opening, preventing refrigerant from reaching the evaporator; the blower resistor is burnt out, leaving only minimum fan speed; or the evaporator temperature sensor is malfunctioning and sending erratic data. You can first try turning the fan to maximum speed and listen for gear shifting sounds from the blower - if there aren't any, go check the resistor. Nowadays, new cars all have fault codes - if the OBD scanner shows inaccurate evaporator temperature readings, it's basically a dead sensor. Don't trust those repair shops that just want to add refrigerant, they're the best at giving you the runaround.
