[C4JDB]

For some reason, my cooling fans no longer want to come on. Car is a '96 LT1 and has two fans.

I've checked / replaced the relays and that didn't help. I can jump the relays (the two 4 pin relays) and get each fan to come on. I'm assuming that with the AC turned on, both fans should be on full time.

Since I can get the fans on by jumping the relays, I'm guessing the problem is somewhere upstream of the relays. What all should I be checking there? The AC is turned on (AC doesn't have any freon in, but hasn't had in along time). Also, even when the temp gauges shoot up showing the car getting hot (higher than 240), the fans still don't come on.

Another question - what is the location of the two temp sending units for the two gauges, digital & dial?

 

[vetteoz]

what is the location of the two temp sending units for the two gauges, digital & dial?

Digital is from the CTS that the PCM uses; located in the water pump
Analog from sensor in head ( pass side ? )

Car is a '96 LT1 and has two fans.

IIRC '96 should have three
a single in front and two stacked slightly behind.

AC doesn't have any freon

Fans are not going to work with A/c then
A switch sees the line pressure change when A/c is running and sends a signal to the PCM which turns the fans on

 

[ND4g]

Mine is an '85, so it may be different. If you can find where the sensor from the block plugs into the harness, you may be able to simply unplug it, forcing the fan to always run.

 

[vetteoz]

Mine is an '85, so it may be different.

Completely different setup

If you can find where the sensor from the block plugs into the harness,

If you are unplugging a sensor in the block ( on any C4 ) it has nothing to do with temp.
The temp sensors are in heads / intake (L98 ) or waterpump (LT1 )

 

[ND4g]

Completely different setup


If you are unplugging a sensor in the block ( on any C4 ) it has nothing to do with temp.
The temp sensors are in heads / intake (L98 ) or waterpump (LT1 )

Acknowledging that it is a different setup, then the point is mute.... however, my suggestion was given that the connection into the harness appears to the computer as a thermister/switch and with a high resistance (open or disconnected) the computer interprets this as "hot" and therefore turns on the fan. Thus with the pigtail disconnected, the fan will always run. Translate the logic/idea to how it applies to the year/model 'vette in question and you can see my point is still valid.

 

[vetteoz]

with a high resistance (open or disconnected) the computer interprets this as "hot" and therefore turns on the fan.

All very well but the coolant temp sensor the ECM references is at front of intake on TPI cars;
the one you show is the temp gauge sensor on '86+ cars / the direct fan override switch on '85 cars ( bypasses ECM control ) or the mech fan switch on a '84 car ( no ECM control of fans)