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Correct assessment, except that AC on will trigger both fans at low speed operation, which indeed happens on my car (How I know both ballast resistors are operational as well as low speed fan relays).
If the low speed fans were already activated and the AC is turned on, high speed fans are activated. I have also witnessed this behavior and both high speed fans work (eliminating the relays as culprits).
It is the following specific behavior that causes my issue:
slow driving(traffic), AC on, low speed fans operational. Uphill climb, mid-speed operation, low speed fans stay on, temperature rises. Temp rises above the 217 mark and high speed fans will not activate (I expect them to activate here). In a few circumstances, temp will rise to 223+ (via OBD readout) and high speed fans still not active. At that point, I turn off AC and the low speed fan operation will bring the temperatures down. I have in some rare cases, seen the high speed fans activate following the previous situation, but my assumption was that it was due to AC pressure, since the temp was higher than the 217 mark and in other instances, the high speed fans did NOT operate at that temperature.
I expect the high speed fans to kick in whether the AC is on or off, at 217F. Does anyone know if this is true? Is it possible that the high speed fan operation occurs at a higher temperature when the AC is on to help some component of the AC stay cold/equalize pressures???
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