I was telling a coworker about my cooling fan problem at work today. ( Fans DO NOT come on at all even with ALDL jumped)
He was telling me about a fan switch on the pass side head behind the dipstick tube, and how the plastic plug melts off and loses the connection. Is this correct b/c I thought the fan switch was on the driver side head. I somewhat belive it is true b/c he is somewhat of an Fbody guru.

 

The unit in the driver side head is the sending unit for the gauge.

 

OK But what is the one on the pass head.

 

passengers side head = fan switch controls passengers side fan.

drivers side head = temp gauge sendor

coolant temp sensor infront of the manifold.

 

The sensor on the passenger side head is what sends the signal that turns the fan on when it reaches 235 degrees. My car only has one big fan, and not 2 fans like the z28's I have mine run Manual to a toggle switch so I can turn it on and off when I want, its a simple ground switch.

 

Primary cooling fan is ECM controlled. If it is not coming on at all, you need to find out why. Chances are, it's just a failed relay. Secondary fan is controlled by temp switch in pass. side head, and also, pressure switch on A/C compressor. turns on at like 235 degrees, or, when A/C pressure gets to a certain point. (don't remember the exact pressure.) The ECM also pays attention to the secondary fan circuit. It senses when the fan comes on by checking for voltage on the ground circuit. So, when the secondary comes on, for whatever reason, the primary should come on as well.

You can test your fans by simply turning the ignition on, and grounding the secondary fan switch. (either one....) both fans should come on.

Hope you like electrical troubleshooting, sometimes, these can be fun. I beleive, if you look in the tech section of this website, you can find a tech article on fan control.

Good luck.