87 Odd ball cooling fan wiring
11-10-2016, 05:55 PM
#1
Le Mans Master
Thread Starter
87 Odd ball cooling fan wiring
I removed all of the added ineffective cooling fan wiring from my 87 and put it all back to stock. The system now works properly. Today I had to pull the interior apart and I removed a miniature 2 pole double throw center off switch that was supposed to ground the green wire that signals the computer to turn on the fan. Only half of the switch was being used, so in effect it is a single pole double throw center off switch. Both of the toggled pins were connected to the green wire in the engine compartment. So which ever way the switch was flipped except center off, the green wire was grounded. The center pin was grounded near the shifter. Here's the weird part: There is a diode across the two toggled pins. Anybody see anything like this before? Just curious as to what Einstein was trying to do.
11-10-2016, 08:41 PM
#2
Safety Car
Is one end of the diode connected to the center (ground) pin, or were the two ends of the diode connected to the two outside (toggled) pins?
Do I understand correctly that the two outside pins are both connected to the green wire?
Do I understand correctly that the two outside pins are both connected to the green wire?
11-11-2016, 09:11 AM
#3
Le Mans Master
Thread Starter
The diode is across the two outside pins. The two wires on the outside (toggled) pins were both connected to the green ECM wire. The whole mess doesn't make sense to me. They also had a switch installed that ran +12V directly from the battery to the fan. There was a piece of mechanics tie wire inserted where the aftermarket push in fuse should have been for that circuit. LOL It's all gone now.
11-11-2016, 04:45 PM
#4
Safety Car
The diode is across the two outside pins. The two wires on the outside (toggled) pins were both connected to the green ECM wire. The whole mess doesn't make sense to me.
There was a piece of mechanics tie wire inserted where the aftermarket push in fuse should have been for that circuit. LOL It's all gone now.
There was a piece of mechanics tie wire inserted where the aftermarket push in fuse should have been for that circuit. LOL It's all gone now.
You are so right, this wiring makes no sense! The mis-guided Einstein knew just enough electronics to get himself in trouble!
The diode was an attempt to provide an "arc supression circuit" to the coil of the fan relay. This is a good idea, and this will improve the reliability of the Coolant Temperature Switch. But the diode needs to be installed between the +12 v. side of the relay coil and ground. His way is totally useless!
If you are interested in doing your own experiment to see how this works, it's easy, and it's quite surprising!
Here's the circuit I'm talking about:
First, use any automotive relay, but no switch, just two pieces of wire that you can touch together to actuate the relay. Don't use any diode yet.
Apply the 12 v. to the "relay only" circuit Touch the wires together, then watch for the small arc as you disconnect the wires. It's easier to see if the room lighting is dim.
Next, solder a diode to the relay, with the cathode (stripe) toward the 12 v. Try the test again, watching for the arc as you disconnect the wires. The arc is gone!
As you disconnect the wires, the inductance of the relay coil forces current to continue to flow for a tiny bit. With the diode in the circuit, this current can flow thru the diode, rather than creating the arc in the switch!
(Please, some might want to argue about which direction current flows. That's not the purpose of this post!)
11-13-2016, 08:16 AM
#5
Le Mans Master
Thread Starter
The fan motor was "good" but worn & loose. I drove the car from Rocky Mount NC to Raleigh NC when I bought it. I had to monitor the temp and turn the fan on as needed.... it worked but was annoying. That's circuit is pretty interesting. Why not just put a capacitor across the terminals? Too much current?
11-14-2016, 08:56 PM
#6
Melting Slicks
I removed all of the added ineffective cooling fan wiring from my 87 and put it all back to stock. The system now works properly. Today I had to pull the interior apart and I removed a miniature 2 pole double throw center off switch that was supposed to ground the green wire that signals the computer to turn on the fan. Only half of the switch was being used, so in effect it is a single pole double throw center off switch. Both of the toggled pins were connected to the green wire in the engine compartment. So which ever way the switch was flipped except center off, the green wire was grounded. The center pin was grounded near the shifter. Here's the weird part: There is a diode across the two toggled pins. Anybody see anything like this before? Just curious as to what Einstein was trying to do.
Here is a wiring diagram if you need it, I have an adjustable t/stat to control the main cooling fan.
Ground to t/stat to green / white wire that goes to ecm, will maintain whatever temperature I set it to.
And doesn't interfere with factory wiring allowing things like a/c fan request to run the main cooling fan.
if anything goes wrong with the adjustable thermostat it can revert to factory ecm temp control.
Last edited by gerardvg; 11-14-2016 at 08:57 PM.
11-15-2016, 01:33 AM
#7
Safety Car
11-15-2016, 03:56 AM
#8
Le Mans Master
Thread Starter
Hi
Here is a wiring diagram if you need it, I have an adjustable t/stat to control the main cooling fan.
Ground to t/stat to green / white wire that goes to ecm, will maintain whatever temperature I set it to.
And doesn't interfere with factory wiring allowing things like a/c fan request to run the main cooling fan.
if anything goes wrong with the adjustable thermostat it can revert to factory ecm temp control.
Here is a wiring diagram if you need it, I have an adjustable t/stat to control the main cooling fan.
Ground to t/stat to green / white wire that goes to ecm, will maintain whatever temperature I set it to.
And doesn't interfere with factory wiring allowing things like a/c fan request to run the main cooling fan.
if anything goes wrong with the adjustable thermostat it can revert to factory ecm temp control.
Single fan though.... no dual fans. That changes things a bit. Only one CTS for the fan and it is not discrete.
11-15-2016, 03:57 AM
#9
Le Mans Master
Thread Starter
I returned all wiring to factory. The factory relay was missing but the connector was present.
11-17-2016, 06:22 PM
#11
Le Mans Master
Thread Starter
11-17-2016, 09:13 PM
#12
Safety Car
Hooking up the relay to 12 v. backwards will destroy the diode!
11-18-2016, 10:01 AM
#13
Le Mans Master
Thread Starter
If you don't believe it, you can test for the diodes with a multimeter. Reverse the test leads on the relay coil terminals. The resistance will be higher in one direction than the other, and the relay will probably have a diode symbol shown on the case.
Hooking up the relay to 12 v. backwards will destroy the diode!
Hooking up the relay to 12 v. backwards will destroy the diode!
11-18-2016, 10:07 AM
#14
Melting Slicks
Member Since: Jan 2014
Location: Downers Grove Illinois
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If you don't believe it, you can test for the diodes with a multimeter. Reverse the test leads on the relay coil terminals. The resistance will be higher in one direction than the other, and the relay will probably have a diode symbol shown on the case.
Hooking up the relay to 12 v. backwards will destroy the diode!
Hooking up the relay to 12 v. backwards will destroy the diode!
