When you get home you pop the hood with the engine running and not quite overheating and with the A/C on, you see the electric cooling fans aren't running. You think to your self; "Self, why are the radiator cooling fans not running?" The Powertrain Control Module (PCM) may control the radiator cooling fans, but the basic circuit is pretty straightforward.

On almost every car I've ever worked on, the radiator cooling fans should come on when the A/C is turned on. Maybe not instantly, but within a minute or so. If they don't, you have some detective work to do.

Whenever you look for an electrical problem, the first things you always check are the fuses and fusible links. On newer models it is a fuse in the under hood fuse box and on older models it's a fusible link. Pull the fuse out and look at it. If it is blown, simply replace it. If it looks good, check it with a DVOM just to be sure. I've been bitten enough times by fuses that looked good. A fusible link is a short section of wire three or four gauges smaller then the wire it's protecting. If it looks burnt, replace it. Even if it looks good, pull on the ends. If it stretches, the wire inside is burnt or broken.