Fan Switch Circuit (Page 2/2)
Blacktree SEP 23, 10:31 AM
That red connector doesn't look familiar. But then again, I haven't touched an Iron Duke engine in years. Maybe it goes to the A/C compressor? The compressor should have a fan switch on it, also. And it grounds out the green/white wire, just like the fan switch on the intake manifold. But the fan switch on the compressor is pressure based (refrigerant pressure) rather than temperature based.
theogre SEP 23, 12:48 PM
I think Duke Engine harness are All make for 2 speed rad fad but red connector goes nowhere on 85-88.
GM made Thousands of Wiring Harness parts and many have "extra" plugs that go nowhere unless you have X option. Why? Because easier and cheaper for them to ignore some wires vs. make more PN w/ exact wiring.

Even PN to inventory can easily cost 10's of Thousands of $.
Example: GM already made several "Cross cabin" harness for Door Options and 2 min 84 front harness and 1 and 2 speed fans and each one causes cost for GM to design, make, storage at many stages, inventory them too, and more handling on the factory floor.
While many use JIT to make a car now to not inventory and store parts car's factory, most parts are still in inventory somewhere because many made X part in batches and go on to make Y for some other thing. Someone is paying for that and you pay in the end.

Red connector and whatever wire isn't mention in any book showing 1 speed fan...
Maybe 85-86 just wired to same 1 speed wire and relay and turn on if shorted to ground.
87-88 has fan control under ECM that will turn on rad fan at 2 temps. Maybe even so, red con is wired as backup or just made engine wires before ECM type/programing was selected.
Patrick SEP 23, 03:30 PM

quote
Originally posted by mkoski:

It strongly points to a bad switch in the head or the switch is not submersed in coolant since when I ground the wire the fan turns on.



Do you suspect an air pocket? Have you followed the proper procedure for "burping" the coolant system? My variation of the technique is Here.
mkoski SEP 23, 04:29 PM
I agree with ogre that red connector was full of old oil and fine debris. May well have never been connected to anything on this unit, but it is certainly part of the fan circuit, ground the Green/white and the fan comes alive. Now the other green or maybe it has a white stripe too I can’t tell also turns on the fan when grounded. So under Ogre’s conclusion that must mean these two greens are tied together in the loom and the guy on the line just connected the one called for in the build sheet attached to the sub assembly. Or left over 1984 inventory.

I’m confident this engine has never been out, it belongs to this chassis.

An air pocket, yep a real possibility. Or I have gotten two faulty switches that’s about all that is left.

The overflow tank holds the level seems right I’ve run this through half a dozen thermal cycles taken it for a ride at various highway speeds. Still though could be a pocket that comes around the corner and stalls.
Patrick SEP 23, 05:14 PM

quote
Originally posted by mkoski:

The overflow tank holds the level seems right I’ve run this through half a dozen thermal cycles taken it for a ride at various highway speeds.



Not quite sure what you mean by "holds the level", as the overflow tank level should go up every time the engine reaches operating temperature, and then go down again when the engine cools off.


quote
Originally posted by mkoski:

An air pocket, yep a real possibility. Or I have gotten two faulty switches that’s about all that is left.



If one of them is a Dickman supplied 210° on and 200° off fan switch, it would be easy enough to check with a continuity tester while in a pot of hot water on the stove.

[This message has been edited by Patrick (edited 09-23-2020).]

Blacktree SEP 23, 05:26 PM
Sounds like you've ruled out just about everything. In a previous post, you mentioned the fan switch changing from open circuit to ~7 Ohms when the engine gets hot, so that switch is good. Also, the fan and relay are good because you can activate them by jumping to ground.

The only thing I can think of is the ground path from the fan switch to the battery. Just out of curiosity, have you tested the resistance from the body of the fan switch (i.e. the part where you put a wrench) to the intake manifold right next to the switch? The resistance through such a short distance should be a fraction of an Ohm. If it's more, then maybe the threads in the engine need to be cleaned out, as well.
mkoski SEP 23, 05:46 PM
Issue resolved:

$15.00 pulled the last switch out replaced with the called for Napa part number. Fan comes on about 225-230 goes open at 210- 215.

I just need to get the new A pillar gauge in and the younger son can have his Fiero back. His mother gets her Thunderbird back and everyone is happy.

Thanks to all for the suggestions.
Patrick SEP 23, 05:58 PM

quote
Originally posted by mkoski:

Issue resolved:

$15.00 pulled the last switch out replaced with the called for Napa part number. Fan comes on about 225-230 goes open at 210- 215.



So the other two fan switches were both faulty?
mkoski SEP 23, 06:13 PM
Looking that way the switch was the only thing touched today.
Patrick SEP 23, 06:54 PM

Would be interesting to know the results...


quote
Originally posted by Patrick:

If one of them is a Dickman supplied 210° on and 200° off fan switch, it would be easy enough to check with a continuity tester while in a pot of hot water on the stove.