Big Bird 88

So here is the deal. Aux cooling fan does not work.

Turn on AC, both fans are supposed to come on, Aux does not.

Disconnect Aux fan from wiring harness and put 12v on it - IT RUNS so I know the fan is good.

Replaced the relay with a known good relay - no fan.


The only thing I have not tried that I can think of is run the car to 230 and the fan should kick on at 228 or 229.

I suspect it is a fusible link issue. FSM says fusible link D or E cant remember right now.

Question is, how do I identify the exact link and how do I test it?

If it is bad can I bypass or should I replace it ? Can I use a fused link instead ?

What says the brain trust ?

antfarmer2

Not sure but think that sensor is on the pass side in the middle and only comes on when up to temp.

Cliff Harris

The auxiliary fan in front of the A/C condenser is not controlled by the ECM until 1990. It's all done by the coolant temperature switch in one of the heads (passenger side in '84 and '85 -- driver's side in '86 and later).

The best way to test the auxiliary fan is to disconnect the coolant temperature switch and ground the wire. The relay should energize and the fan should run.

BlowerWorks

Cliff is right ON ! And that sensor switch can be replaced with a lower temp unit if desired.

WVZR-1

This is NOT how an '88 AUX FAN works - AUX is TEMP CONTROL ONLY!

Proper check of the AUX FAN circuit requires a fused jumper and test light - don't go wildly searching for a fusible link issue even if grounding doesn't turn on fan. The fusible link would be the "last stop" I'd think.

If you have a FSM it's very well covered in the diagnostics.

Big Bird 88

WVZR-1
thanks that's what I was looking for. Temp control only.
I've read in several other threads here that if you put the AC on all the fans run.
FSM ELECTRICAL suplemental helped a little with the wiring diagram. But the manuals assume a level of expertise and tools than not everyone has.

I understand what you say about the fusible link but the manual basically said if you put power to the fan and it runs check the relay if the relays good check the fusible link.
I guess the only way to be sure is to run the engine up to 229 or 230 then get under and look.

frank j. moran

The secondary fan comes on when eng temp is around 235F, or under certain AC conditions. Simply go to the ALCL diagnostic link in the car under the left side dash , connect A and B with a jumper wire, turn on the ign. switch, engine off. Both fans should go on. This should eliminate the fuse link.

Big Bird 88

Tried the jumper last night.
Only the primary fan runs when I do that.

frank j. moran

Did you replace the relay for the secondary fan? I believe it is up on the radiator left side shroud.

Cliff Harris

That's only true for 1990 and later where the ECM controls both fans. See post #3 in this thread.

Big Bird 88

Hi Cliff
Is the aux cooling fan relay the one mounted on the left side of the primary fan shroud ?

WVZR-1

If you don't have the FSM I'll help you with an image of the AUX FAN relay location.

Just ask.

***** I had checked a couple other year FSMs and the '88 seemed "odd" as it seemed to be somewhat dissimilar and I do have an '88 SUPPLEMENT and that location has been changed in the SUPPLEMENT. In the supplement the AUX is located on the shroud. The original FSM is incorrect BUT the supplement says LATE PRODUCTION so ....

AGENT 86

That's where it is on my 86.

Have you tried removing the connector from switch and grounding the wire, as Cliff mentioned ?

WVZR-1

In the SUPPLEMENT I have here's a list oif the ELECTRICAL REVISIONS:



This is FSM LOCATION OF AUX RELAY "ASSUME TO BE WRONG (?)"



This is SUPPLEMENT LOCATIONS "ASSUME TO BE CORRECT (likely)"

Big Bird 88

Agent 86
I have not. Don't know what the switch looks like.
WVZR-1
I will tell you again, yes I have the 1988 corvette service manual, the 1988 corvette electrical diagnosis service manual supplement , the Haynes Chevrolet Corvette 84 thru 96 manual.
I am a car novice at best, this is the first car I have had in 30 years that I have done anything myself on and I find the manual assumes a level of knowledge of the vehicle I just don't have.
If the answer to every question is read the manual, this place would be of little benefit to anyone.

As you can see in your post even you seem confused as to te location of that relay.

I found the wiring diagrams in the electrical supplement helpful in this instance. While they tell you what's connected to what it does not give clear locations of the components. For example the manual said the fusible link for the auxiliary cooling fan is near the battery. It labeled it as fusible link D or E I can't remember. I don't know about your vehicle but when I look at the battery in my vehicle there are several fusible links and none of them appear to be labeled. That is just an example of how frustrating I find the manual to be.

WVZR-1

I looked at the FSM and the supplement after you asked "is it the one on the shroud?"! If you asked the question it "hinted" that you must have one there so I looked further!

Fusible links can certainly be a challenge BUT if you've B+ voltage to the circuits first stop you know that you don't have a fusible link failure.

This description of the AUX FAN CIRCUIT is likely all you need to check "first".

AGENT 86

The temp switch is in driver side head. It has a connector that looks like this.
Sqeeze the flat sides of connector, to release it from switch.

Cliff Harris

This is my auxiliary fan relay (right in the center of the picture):



This is the location of the auxiliary fan thermal switch (between spark plugs #1 and #3):



I usually test the circuit by touching the center pin of the connector to a screw on the alternator.

Big Bird 88

Agent 86 and WVZR-1 thanks ! that was a big help.

Cliff : I don't think I have a relay in that location, I have one on the back of the shroud in about that position near the primary cooling fan, but I will check again tonight and post here.

WVZR-1 I think I get what you are saying. With the ignition in run, If I get voltage off D and E at that relay, then I have eliminated the fusible link right ? and if I do, since I have checked the fan itself it is either the relay or the temp switch.

I'll also try and ground out that switch and see what happens.

WVZR-1

Yes that's the first check I'd think and in my post with the images your AUX RELAY should be where the "SUPPLEMENT" mentioned. The smaller of the images on the left. If you've power to "both" grounding the wire as Cliff mentioned should turn ON the fan.