First off:

- verified the motor was good by hot wiring it to the battery
- verified the connector is good by inserting a wire into the connector and battery
- new relay
- new coolant temp sensor
- new thermostat

The fan won't turn on with the engine temperature nor AC. The engine WILL overheat unless it comes on (re: me hot wiring it), whether it's idling or driving. I have no clue what it could be, and I can't drive it right now (did I mention it's my DD... ) because it'll overheat. Any ideas?

 

Well, we need to know how many fans you have and which engine. You should fill out the profile stuff for your car. At any rate, the relay supplies power to the fan and it is hot all the time. The coil of the relay is grounded by either the A/C operation or a cylinder head temp switch (in the case of a single fan system). Make sure the fat hot wire going to the relay is in fact hot. Make sure one of the coil wires on the relay measures 12V when the key is on. You can test all of this at once by just grounding the other relay coil wire when the key is on. The fan should run. If it does, then it's in the grounding side (temp switch, A/C). If not, then it's in the power supply side of things.

 

Whoops, sorry bout that. 86 305 TPI, so single fan setup.

It's definitely in the grounding of things, because it all runs when directly hooked up to the battery. The A/C compressor doesn't work and doesn't kick on, would this prohibit the fan from kicking on? Otherwise, it doesn't. What is the difference between the coolant temperature sensor and the head temp switch? I was under the impression (from what I've read here) that the CTS controls the rad fan. That's been replaced.

 

On a dual fan setup, the ECM turns on the primary fan when it reads a high temp on the CTS.

On a single fan setup, there is a switch in the head that actually turns on the fan. It is paralleled by the A/C so that the fan runs when it is on also. The ECM and CTS have nothing to do with it.

There are 305TPIs that have dual fans by the way.

 

Interesting. So would the AC compressor being dead cause the fan NOT to turn on with the AC? It doesn't turn on with temp nor AC. It still blows air, just not cold.

I bought an adjustable fan controller to completely bypass the stock setup. I can't get to the plug in the head anyway.

Interesting fact about the fan[s]. So there are some '86 IROCs out there with two fans? I need to find me that setup, my engine runs too hot

 

Based upon my 1990 FSM, the act of turning the controls to an A/C position should make the single fan run. There is a dark green wire going into the control head that is grounded when the switch is turned to an A/C position. This grounds the relay turning on the fan.

On the adjustable controller, I'd go ahead and put a manual override switch in also. It should have a wire for that. I have one in my project truck and it didn't last very long before it stopped working. I temporarily wired it to run all the time. I'm going to switch to a non-adjustable version hoping that it will be more reliable.

I don't know for sure about dual fans on a 1986 305, but they sure had them in 1990.

 

Doesnt the AC compressor have to build up a certain amount of pressure before the 2nd fan kicks on? And if all the refrigerant has leaked out, then it may never build up to that pressure?

 

Yes, in a dual-fan setup that's how it works. But in a single fan, it works thru the control head and not a pressure switch.