About a month ago, my a/c started only blowing one speed, low, no matter what I set it on. So far, I have replaced the fan speed switch, the blower motor, and as of last night, the blower motor resistor. Still only getting low speed. I ran a connection from the blower motor directly to the battery, and it started spinning so fast it damn near took off! So, the only thing I can think of is that it's a voltage issue. Any thoughts?

 

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I recommend you put the original parts back on; they're higher-quality than the replacements.