The low speed of the fan is ECM controlled. Turns on at about 198*F. The high speed of the fan is controlled via the temperature switch. It is located someplace on the front of the intake manifold (has single grn/yel wire).
The pressure switch on the A/C compressor will also control both the low & high speed fan relays.
The third larger fan relay is a delayed off relay. This causes the fan to run after the ignition has been turned off. This is done when the fan was running on high at that time. This relay commonly goes bad and causes the fan to run at inopportune times, which drains the battery.
