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Q: Strange whirring noise coming from the engine

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We recently drove to North Carolina and back, approximately 1400 miles. Before the trip, I replaced the blower motor and resistor under the dash, because the fan would only work on setting 4, and the blower was sounding bad. Everything worked great for about 400 miles, besides the a/c blowing semi cool air. After driving for many hours and stopping for lunch, we continued our journey. Shortly after, mist started coming from the cents and our semi cool air now, had become warm. Not hot, just not cool. I took it as the Freon being low or empty, so we turned the a/c off for the rest of the entire trip. When we returned home, I purchased a bottle with a gauge to recharge the system. I did not use the entire can, but still managed to overfill it. By a little research, I found I could bleed it. I bled very little, and the a/c was working great. After about 3 hours of driving, the warm air returned and a fairly loud whirring sound started in the engine. Sound stops when car is off

My car has 100000 miles.
My car has an automatic transmission.

It sounds like you are getting water built up inside the evaporator housing and need to unplug the A/C drain or you will flood the evaporator, blower motor, and resistor with water and short the motor and resistor again. If you’d like a local expert to check this out, a certified technician from YourMechanic can come to your home or office to inspect the A/C system and whirring noise in order to determine what fixes should be done.

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