Manually Control the Cooling Fans

Manual
control of your cooling fans
I have a 92 LT-1 convertible with the
6-speed transmission. I, also, have a Meziere HD electric water pump
installed. This Tech Tip will explain how I installed switches that allow
me to turn on the primary and secondary cooling fans. When the switches
are turned off, the ECM regains normal control over the cooling fans.
Placement of the switches is up to the owner, but I will explain where I
installed mine.
List of materials (things you need to get):
14-16-gauge wire, I chose colors to match the wires I spliced into. (green
and blue for my car)
Two rocker switches, just on-off type (don�t
get the lighted rocker switches).
Hardware to mount the
switches
Some tie wraps
Electrical tape
Soldering
gun and solder
First a lesson on how the fans work on a 92
Corvette. The 92 uses a primary and secondary fan system, as compared
with the two-fan system that uses low and high speeds used in later
models. The ECM controls the fans by grounding the signal circuit of the
relays. The ECM first turns on the primary fan when it reads a preset oil
or coolant temperature. At a higher temperature, the ECM will turn on the
secondary fan for additional cooling. There is also an input to the ECM
from the VSS (vehicle speed sensor) that turns the fans off at certain
speeds. When the A/C is turned on, the fans are also turned on.
What we�re going to do is intercept the ground side of the signal
circuit of the relays and put a switch inline to ground. Once grounded,
the signal circuit is complete and the relay closes and the fans come on.
Simple.
Now, let�s find the two relays that control the fans. They
are located on the driver�s side of the engine compartment mounted on the
side of the radiator housing. Notice that each relay has four wires
running to them. Two wires are heavier gauge and two are lighter gauge
wires. Of the two lighter gauge wires, one is �key-on� power and the
other goes to the ECM for grounding. You can identify the �key-on� power
by its color. Both relays will have this same color wire going to the
relay. Once you find this same color wire running to both the relays,
the OTHER lighter gauge wires are the ones going to the ECM and they are
the ones we want to work with. On my 92, the primary fan relay ground
side of the signal circuit is green and the secondary one is blue with a
white stripe. I unwrapped these two from the harness wrap so I could work
with them. There is a very convenient ground just aft and below the fan
relays. If you choose to put your switches in the engine compartment, this
is a good place to mount the switches. I placed my two switches in the
center console inside the cockpit. I never used the cup holder so I
removed the rubber lining and fabricated a switch panel that fit right
over the cup holder. That way I could cover the switches with the lid
that slides in and out. I used the ground wire that is part of the
accessory plug in the console to connect to one side of the switches.
Then, using colored wires for identification, I ran the two wires from the
switches to the engine compartment. Yes, I removed the lower trim panel,
to gain access to the grommet that holds the hood release cables which is
where I ran the wires through the fire wall. (Hardest part of the project)
Now, just make the connections, primary ground side signal wire splice
wire to switch. Then, secondary signal wire to the other switch. I
soldered these connections and taped very well and stuffed them back into
the harness wrap. Reconnect the battery and turn the key on. Turn the
newly installed primary cooling fan switch on and you should hear or see
the primary fan come on. Try the secondary switch also. You�re
done!
A few notes about the use of this modification, These fans
are high draw items and will run your battery down if you turn them on and
forget them. At the track, I�d use your tow vehicle and a set of jumper
cables so you won�t let �Murphy’s Law� get you. For normal driving,
turn them off once you are going into cruise mode. This mod along with
the electric water pump allows you to keep the C-4 a lot cooler. Besides,
I just love switches.;-)
Strick