electric fan pin 33 and 42

[h2bob]

Hello,

From my research the PCM on pre-2007 trucks with electronic fans contains two output pins; pin 42 and 33. I know that on 94-96 B-body vehicles (pin A-10 and A-11), fan 1 turns on when temperature is 225F and or A/C head pressure is above 189psi. Fan 2 turns on when temperature is 232F and A/C 240psi. Both fans do not come on when vehicle speed is above 45 mph.

Can anyone clarify how pins 42 and 33 are used on pre-2007 trucks (assuming that 2007+ use variable fan speed controller) with electric fans?

Most people who install en electric fan setup (replace mechanical fan) enable pin 42 only, why?

Can U7193 control the ON/OFF temperature of both fans?

Also it seems that with the Nelson Performance electric fan wiring harness one of the fans will always be ON when the A/C is ON. With correct wiring to the PCM I think that both fans will remain off when certain speed is reached as the cooling is done by the wind.

Thanks.

[h2bob]

For anyone else who is interested the answer can be found here:

http://www.silveradoss.com/forums/index ... ntry531884

In summary, pin 42 is used to turn on fans on low speed and 33 on high. Works similar to the B-body setup except fans have two speeds.