VA1991Z28

iTrader: (1)

I need some advice/instructions on how to test my secondary fan wiring. Here is some background: 91 Z28 305 TPI 5-spd. I have dual fans, my primary works as it came from the factory. I fried something in my secondary fan wiring while attempting to install a manual fan switch - what I was doing was back probing the fan relay to make sure I had the right wire. Well an old harness and a little color blindness and I grounded the brown wire install of the grey. So neither fan worked then. I found a blown fan fuse under the dash, replaced that and the primary is working again, but no secondary. I can run he car until the temp gauge reads 220 and flip on the A/C, and the primary comes on, but no secondary. The secondary used to work prior to this. The fan motor is new and still works if I apply 12v to it. I also know that the fan relay works, I swapped it with the primary which works, but still nothing. I replaced fan switch last year. So I think its somewhere in the wiring, but I'm kind of green with the wiring/electronics on the car. I have the GM shop manual and access to a volt/ohm meter, I just need some basic how to's and directions on what to check/look for and how to check it so I don't fry anything else. I found fusible link D, (by the battery) and it looks ok, but how do I test it? What do I attach the meter probes too? Do I probe one wire from the relay and one at the fusible link (continuity - sp?) test? I only see two red wires going into the fusible link and one red & one black/brown coming out. I'm a little gun shy after frying something the first time, any directions would be great.

Thanks,
VA1991Z28

BigBadLou

iTrader: (3)

A simple thing you could start off with is rule out the relay. Remove the relay from the connector. Short terminals A and E on the connector. Doesn't matter if the key is on or not. You could use some needlenose pliers or so, open them and touch terminal A with one end, then touch terminal E with the other end. There will be a small spark, just to warn ya, it is expected. If the fan spins, your power circuit is good.

So now onto the control circuit.
Next thing you can do is to test the connector relay. Measure voltage on pin D (with key on). That means, set your voltmeter to DC voltage (either put it on auto or choose range higher than 12V) and then put the negative (black) probe on a ground somewhere (bolt on the chassis, engine block etc) and put the positive (red) probe on terminal D of the connector (brown wire). If it shows 12V, that means the relay is getting power, that's good.

Now put the relay back on the connector. With the key on, ground the grey wire on the connector. Does the relay click? Does the fan spin? If not, there might be a problem in the connector itself, possibly.

Don't worry, you didn't fry any fusible links. That's what fuses are for, if something is shorted. If you fried a fusible link, you'd have much more trouble than just the secondary fan.

Let us know what you find!
Lou

VA1991Z28

iTrader: (1)

Thanks Lou, this is exactly what I needed. I'll give this a try. One question, to ground the grey wire with the relay install, what is the best way to do this? Back probe the grey wire from the back of the connector and ground that or do I have to splice the wire?

Thanks again,
VA1991Z28

BigBadLou

iTrader: (3)

No splicing necessary. Backprobing should do the trick.

Lou

pmpn

If the primary fan works your fusible link off the battery is good. The connectors going into the relay are cheap plastic- can easily melt and insulate the wires with enough heat. What other wires have you cut into besides the brown? Are all of your grounds good? Here is a link with an awesome diagram, it's a few posts into it.


https://www.thirdgen.org/forums/elec...ht=primary+fan

VA1991Z28

iTrader: (1)

Thanks for the link. All I probed were the brown then the grey wires. If I need to replace the connector, who carries one? AutoZone, NAPA, ? What's involved in replacing the connector to the relay (cut old one off and run wires into new one)? What holds the wires in the connector?

BigBadLou

iTrader: (3)

Don't worry about replacements connectors now. We don't even know what is the cause of the failure now.

Lou

pmpn

Visually inspect the connector and ensure there is no damage. If it looks good, unplug the connector and ensure you have 12V on terminal D (brown)and E (orange) while the key is in ON. If you have both then you have a bad relay or the relay isn't getting negative via grey wire (temp switch, AC pressure switch.) Also ensure all connectors are connected- fans and switches.

VA1991Z28

iTrader: (1)

Well I ran the tests you guys described and here are the results:
1) Remove Relay, short terminals A & E with needle nose pliers, key off - result: Secondary Fan started to spin. PASS
2) Using voltmeter set to volts dc, I grounded black probe & back probed with positive probe terminal D with key on - result: 11.94 volts so I think PASS.
3) Put relay back in, key on, ground grey wire and wouldn't you know it the fan started to spin.

So, it must be something else (I'm guessing fan switch / wiring - since with car around 220 & A/C on MAX primary comes on). This was working this past summer. I never retested the grey wire to ground after I replaced the blown fuse under the dash.

In any case, thanks a lot for your help. I can now go forward and wire in a manual fan switch to the secondary, which is what I wanted to do in the first place. I tested the switch I bought by grounding one terminal and back probed the grey wire and fan came on and then switched off with the switch. Cool.

What gauge wire would you guys suggest? I bought 16 gauge wire from NAPA.

Thanks again,
VA1991Z28

pmpn

I believe the stock grey wire is just 20g because it doesn't carry current. 16g will work just the same.
It sounds like you have lost your ground at the end of the grey wire or that wire lost continuity somewhere. Just splice into it prior to where it splits to the A/C switch and ground it- bolt to frame or firewall. It HAS to be on the <firewall side> of the AC plug split. Also ensure your A/C switch is properly connected/wires terminated, and is in good condition going all the way to the relay. That way it's there just-in-case you forget to turn the switch on a nice insurance measure. Good luck and repost if you have any questions.