94 lt1 auto. So I've been chasing this problem for a couple of years now. I don't drive the car very often like I used to but my secondary cooling fan has an intermittent problem of working when it wants to. Not sure if this is just normal but my temp gauge sometimes reads just above the half way point and some times it reads about 1/3 both with the a/c on. It can be night or day long trips or short trips. The difference I noticed is the secondary fan doesn't come on when running the hotter of the two. Haynes manual shows the Ecm grounds the relay to turn on the fans. I've replaced the temp sensor and swapped the primary and sec relays around and still the same. What circuits can I check that prompts the Ecm to turn the sec fan on or is this typical for my year car? Coolant level is good and bled it several times.

 

Never mind, found a link by Pete bout testing the fans. I'll try that first.

 

shbox is good here is some more info on cooling system, 4th Gen LT1 F-body Tech Articles

 

It's working as it should. See here from shbox:

1993-1994 - Primary and Secondary fans that operate at only one speed. When initially commanded on, only the primary fan (driver side) comes on. It operates alone at full speed. If the temp threshold is met for addtional cooling, the secondary fan (passenger side) also is commanded on. At this point, both fans are running at full speed.
These fans use a two relay architecture that can be seen in the fuse/relay panel that is under the hood.

 

According to the factory service manual, there was a change in the cooling fan system later in the production year that the above "Shoebox" information doesn't mention. The early production operation is described above and the later production changed to a three relay design that used a low and high fan speed to control engine temps. You don't give enough information to know which system you're working with, but if you have the later, a bad coil in the #3 relay would not allow the fans to change to high speed when the engine reached the higher operating temps. If you're working with the two relay system, a broken wire or a bad connection in a connector may be the problem. I've attached pages from the 1994 Service Manual that may help troubleshooting the problem.

 

Shbox does mentioned the late '94 change, I omitted it because the OP said he swapped the two relays, giving the impression that he has the early style set up.

The problem he described is not that his fans aren't working, but that the secondary fan isn't always kicking on, which is how it's designed to operate. It's not going to run all the time, only when a certain temperature (~235 degrees) is met. And once the temp drops below 230, it will kick back off. He stated the temp gauge only goes to the halfway mark, indicating that there is no overheating issue, telling us that his cooling system is functioning well.

 

I wouldn't disagree with what you said at all, but I would like see what temps a scanner is reading when the fans turn on to verify the dash gage reading. Unfortunately, most people don't have access to a scanner capable of that function. Having access to a Tech 2 scanner would also allow a person to manually command the fans on which would verify the wiring needed for correct fan operation. My main intention in posting was to make others aware that the 1994 model year used two different systems and should not be troubleshooted the same way.

 

Alternatively, you can turn the AC on with the car running. IIRC, that will kick both fans on at high speed, regardless of the system used.But I agree, getting verification of the temps is a must.