If you have a code reader, just plug it in and the first thing that will happen is the fan will cycle both low and high speeds for a couple seconds. You should be able to hear it clearly. This should at least tell you if both circuits are operational. It seems that for me, I can't hear the difference in fan speed for normal and max A/C. My fan wasn't turning on in traffic for the past month and the engine was running really hot, then I swapped out the temp sensor and everything works great now. The old sensor had pretty much an open circuit, no resistance, nothing, hence no fan.