high speed aux fan operation

[jsmith]

my cooling system has not really been acting up all summer and has stood up to the heat waves we've been getting here in the east. i do know that the high speed fan kicks in when temps rise and i had been experimenting with different resistors for the cooling mod. today when i pulled off the sensor harness i was surprised that the fan did not kick in. after about 5 seconds in started up and stayed on for about 10 seconds then went off again. i turned on the AC and the fan went on at low speed. all this time temps were at around 90C. i know that the cooling mod works because my temps never go over 100C even with stop and go driving and AC on. when i stop the car after highway driving the temps go up to around 100C and if they are still up when i restart the engine, the high speed fan kicks in - so i know it's working fine.

i always thought that when that thermosensor circuit was open, the computer knew to turn on the fan at high speed. should i be concerned? i waited for a little bit with the thermosensor unplugged and the fan didn't kick in at all after the initial 10 seconds that it went on (the temps were at a steady 90C). the system seems to be doing its job, it's just that this unexpected behavior stumped me...