cooling fan wont spin

I assume you mean engine fan. The engine cooling fan won't normally engage unless it's overly hot or the AC condenser coil needs additional heat exchange abilities. You don't want an engine fan running all the time ... if it does, you'll know it and wish it would stop. Somebody may have bypassed the dash switch so that it doesn't manually engage the fan. Have you pulled any long hills in the heat and the fan never came on?

 

DEEC-II? ore later DEEC-III?

 

They use air to engage and disengage the fan clutch. The older models need air to engage. The newer models take air away to engage the fan clutch. If your have an older motor check your air lines first to be sure air is reaching the clutch. 80% of the time this is the issue with the older system. Which is why they changed it. If you flip your Manuel switch on dash air should flow to the clutch if it is not then your problem is not the clutch if air is reaching the clutch then your problem is the clutch. I'm a little unsure of which system you have. I'm sure someone else on here will be more familiar with your year motor.

 

Check air switch. Also check battery cables. Had one do that and it had cable that was corroded under insulation in middle . Not near any terminal. Replaced cable and fan comes right on. Weird one but they happen.

 

Big Duker that is a very odd problem. Was there any other symptoms besides the fan not engaging? What year truck did that happen on? Air switch is much more common then a bum battery cable. Seems like other things would be affected with a bum cable.

 

The air line gos in the fan hub on the right side. Do you hear any air leaks at the fan clutch with the key on?

 

pull fuse that is labeled fan, with the engine running. fan should come on then. if not, you got problem.