Cooling fans puzzle
06-04-2012, 12:30 AM
#21
Race Director
The temperature switch in the driver's side head does not connect to the ECM, so it's OK to ground its connector.
Looking at the diagram in post #7 by vetteoz, there is no connection to the E terminals of the two relays. You said you measured close to zero volts on pin E of the relay connector. There are two ways to get zero volts when you measure something like this. Either it's shorted to ground or it's OPEN (no connection).
The way to BYPASS the relay is to short pins A & D of the UNPLUGGED relay connector. This connects the fusible link to the fan motor (left side of the circuit diagram). You should measure the voltage at pin D of the unplugged relay connector to see if the fusible link is OK and 12 volts is getting to the relay contacts. [EDIT: the diagram in post #7 is wrong and what I said above about pin D should be pin E -- see post #24].
You can TEST the RELAY by connecting pin B to ground while the connector is plugged into the relay. This will turn on the relay and if all is OK the fan will come on. The quad driver in the ECM for the relay is "open collector" (highly-technical engineering talk -- I'm an electronic engineer by profession so I'm allowed to use language like this ;-). You will not damage the ECM by shorting this pin to ground. If this REALLY bothers you, you can disconnect the ECM before doing this test.
You never told us if you tried shorting pin A & B of the ALDL connector together. This tells the ECM to turn on the fan (among many other things).
Looking at the diagram in post #7 by vetteoz, there is no connection to the E terminals of the two relays. You said you measured close to zero volts on pin E of the relay connector. There are two ways to get zero volts when you measure something like this. Either it's shorted to ground or it's OPEN (no connection).
The way to BYPASS the relay is to short pins A & D of the UNPLUGGED relay connector. This connects the fusible link to the fan motor (left side of the circuit diagram). You should measure the voltage at pin D of the unplugged relay connector to see if the fusible link is OK and 12 volts is getting to the relay contacts. [EDIT: the diagram in post #7 is wrong and what I said above about pin D should be pin E -- see post #24].
You can TEST the RELAY by connecting pin B to ground while the connector is plugged into the relay. This will turn on the relay and if all is OK the fan will come on. The quad driver in the ECM for the relay is "open collector" (highly-technical engineering talk -- I'm an electronic engineer by profession so I'm allowed to use language like this ;-). You will not damage the ECM by shorting this pin to ground. If this REALLY bothers you, you can disconnect the ECM before doing this test.
You never told us if you tried shorting pin A & B of the ALDL connector together. This tells the ECM to turn on the fan (among many other things).
Last edited by Cliff Harris; 06-05-2012 at 12:47 AM.
06-04-2012, 02:19 AM
#22
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Looking at the diagram in post #7 by vetteoz, there is no connection to the E terminals of the two relays. You said you measured close to zero volts on pin E of the relay connector. There are two ways to get zero volts when you measure something like this. Either it's shorted to ground or it's OPEN (no connection).
http://members.shaw.ca/corvette86/Co...%20Control.pdf
pin E is connected to the battery + and pin A is connected to the fan motor. When I look at my harness relay, I see a red wire from terminal E, and a red/black wire from terminal A, which seem to agree with the picture in the schematics of the link above. What I did to test the fan was to disconnect the relay and short A and E. It turns out that the voltage between A and E is only 0.3V and decays with time after I take the keys off, which seems to agree with your comment that A and E are not what I thought but they may be.
The question is: WTF is going on here?
I am Ph.D. in Aerospace Engineering, so I'm allowed to use language like this
Thanks!
06-04-2012, 08:54 AM
#23
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The schematic I posted is from my 86 factory service manual, don't know what year Rod posted, but it's not 86.
I had a close look at mine, it is actually one red wire direct from battery into black splice cylinder. The other red wire exits splice on same side of input, that wire is for ECM power disconnect. Out of the other side of splice are the 2 orange fusible links which go into weatherpack connector,then they head off, one to each relay.
Terminal "E" should have constant battery voltage, if it doesn't the fusible link is likely toast. It can still look intact, but under insulation, it is open.
You may have only one toasted link, as the booster fan doesn't come on until 238*.
I had a close look at mine, it is actually one red wire direct from battery into black splice cylinder. The other red wire exits splice on same side of input, that wire is for ECM power disconnect. Out of the other side of splice are the 2 orange fusible links which go into weatherpack connector,then they head off, one to each relay.
Terminal "E" should have constant battery voltage, if it doesn't the fusible link is likely toast. It can still look intact, but under insulation, it is open.
You may have only one toasted link, as the booster fan doesn't come on until 238*.
06-05-2012, 12:40 AM
#24
Race Director
Well I did the "eyeball" test, and you're right, Agent86 is right and vetteoz is wrong and I was wrong (followed his diagram).
My relay connector does not have a wire at pin D. The red wire goes into pin E and it is at 12 volts all the time. I think vetteoz's diagram is for the later relay types that have the sealed connectors. I think it was '88 and later for those guys.
Here's the fan circuit page from my '86 shop manual CD. Unfortunately it doesn't show the auxiliary fan wiring at all (and no color):
My relay connector does not have a wire at pin D. The red wire goes into pin E and it is at 12 volts all the time. I think vetteoz's diagram is for the later relay types that have the sealed connectors. I think it was '88 and later for those guys.
Here's the fan circuit page from my '86 shop manual CD. Unfortunately it doesn't show the auxiliary fan wiring at all (and no color):
Last edited by Cliff Harris; 06-05-2012 at 12:58 AM.
06-05-2012, 11:55 AM
#25
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To test fan motor & wire from relay to fan, jumper power directly from Batt + terminal to main fan relay red/blk wire.
If fan runs test voltage between Batt - terminal to relay red wire. If not getting +12 Vdc at the relay red wire, open the weather pack and test there. If no voltage at weather pack problem is with fusable limk, else problem is either in weather pack or from it to relay.
Can the quad drive IC in the ECM be (relatively) easily replaced?
If fan runs test voltage between Batt - terminal to relay red wire. If not getting +12 Vdc at the relay red wire, open the weather pack and test there. If no voltage at weather pack problem is with fusable limk, else problem is either in weather pack or from it to relay.
The quad driver in the ECM for the relay is "open collector"
06-05-2012, 11:48 PM
#26
Race Director
The quad driver can be replaced if you're good (make that GOOD) at soldering. Here's the guy:
http://www.ti.com/lit/ds/symlink/tpic2404.pdf
I don't know where you can get one. Digi-Key, Mouser and Jameco (the obvious places) don't carry them. You might be able to find a source on the Texas Instruments web site.
http://www.ti.com/lit/ds/symlink/tpic2404.pdf
I don't know where you can get one. Digi-Key, Mouser and Jameco (the obvious places) don't carry them. You might be able to find a source on the Texas Instruments web site.