Ice buildup can cause blockage from A/C

Q. I own a 2009 Mazda 3 with a 2.0 liter engine and mileage of 26,000. The air conditioning works fine under normal driving conditions. I recently took two long 600-mile trips in 90-degree weather. After about four hours of driving at highway speeds the cabin of the car started to get warm. The temperature gauge read in the usual range but I noticed the air was not blowing at full force from the vents.

The air was cold and the fan sounded as if it were at full speed but only a minimal amount of cold air was coming through. I tried adjusting the fan speed and I could hear the fan motor change speed but not the air flow. After stopping for lunch the A/C worked fine for another hour before the same thing happened. I repeatedly needed to turn off the air for a period of time to get the full fan speed blowing.

After the first trip all fluids checked out fine. I let the car run for extended periods of time and the A/C operated normally until the same thing happened on the second trip. Any ideas on what would cause this? I am not sure I can duplicate the same condition at a repair shop.

A. It sounds like perhaps you were getting some ice buildup on the evaporator, reducing the air flow. When you stopped for lunch it melted and you were good to go for a while. You may want to have your shop perform an evacuate and recharge on the system to be sure it has the exact amount of refrigerant in it.

The combination of humidity and improper pressures could have caused the problem. Give that a try and let me know how it works out.

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