on the subject of cooling the temperature switch reaches 230 activates the relay fan stays on few seconds untill it reaches 210
what causes the fan to keep runing is it the switch being grounded untill the temprature reaches 210 and the switch gets ungrounded or is it the relay that sends a signal to the fan for a predetermined time 230-210 ?

 

On TPI cars (dual fan) the primary is turned on by the ECM somewhere around 220-230º. The relay is powerd by an ignition switched +12v off the fuse panel. When the when the ECM 'sees' xxxº at the CTS, it grounds the relay making it kick the fan on.

The 2nd fan is hooked to a fan switch located in the pass side head. When the switch reaches 238º, it makes a ground to the block for the 2nd fan relay causing it to turn on.

Certain years, the 2nd fan does absolutely nothing else any other time (I know my 87 is this way). Later years, the 2nd fan was also hooked to the A/C line pressure switch in parallel with the the fan switch making both fans operate when the A/C is turned on.

TBI cars just work off the fan switch & A/C controls.

All fan relays are controlled/turned on by being grounded though (to the best of my knowledge).