Thank everybody !
Mvsgas 's link is very useful though i can not open it(i'am in china,maybe the link was "harmonious")
Haha ,thank you all the same !
In the game manual Page 289:AIM-9 Control (AIM9), rotary OSB 19. Rotary selections include OFF, COOL, SEL. The selected rotary setting is displayed beneath the AIM9 label. There are no other functions. Selecting SEL places HUD in air-to-air mode.
So,in the game,"cool" is just a "label",no function?