There is definitely a problem when you observe that your car’s A/C is blowing warm air instead of cold air. It’s very frustrating especially during hot summer. One reason could be insufficient refrigerant due to some leakage.
But when you encounter this problem and you hear a very constrained hissing sound from the evaporator side (passenger side), then that’s a sign of a malfunctioning expansion valve. One effect also when you have malfunctioning expansion valve is that the engine idle speed drops significantly when the compressor motor kicks in.
When your car aircon blower stops working on lower speeds (commonly speed “1”), then the most likely culprit is the blower motor resistor. Usually when you have resistor damage, the blower would still work on the highest speed (“4”). The figure below shows the typical blower motor resistor diagram.
So when your car A/C blower stops working, there’s a quick fix to make it working again. And you don’t need to spend money or go to the auto repair shop when you can do it yourself easily.
Here is what I did and the blower is still working for more than a year now. First, I needed to locate the resistor. The usual location is near the blower motor behind the glovebox in the front passenger seat. Second, I removed the glovebox and then the resistor. Third, I checked for broken wire coil connections and joined them by twisting the wire ends together. And finally, I put back the resistor and the A/C was up and blowing cold air on all speed settings!