C5 Fan Controller

This is a
Word Doc that was posted by one of the CF members regardin wiring a
cheaper alternative for controlling fans with.
C5 Instructions for
Installation of the $39 Hayden adjustable Fan control module.
\”Ersatz928\” (corvetteforum.com)
Readers are advised that this
article is for informational purposes only. No liability is assumed by the
author for the use or interpretation of information contained within this
article — all decisions based on the data or information are the
responsibility of the individual user.
This module is sold by
various Corvette vendors for about $150 to $200. The same exact unit
available from PEP Boys Auto stores for $39, and sold under the OEM
manufacturers name
\”Hayden\”. It is usually found near the
aftermarket electric radiator fan kits, often
behind the parts
counter. You may have to look yourself, as some store employees
have no
idea what you are talking about. It is packaged in a clear plastic box.
This installation assumes you have some soldering skills, and are
familiar with basic
automotive electrical and mechanical concepts. If
you can get a copy of the instructions provided with the vendor versions
of this module, no soldering is needed, as crimp connections are used.
These crimp �Scotch-Lok� products tend to be less reliable than a soldered
connection. Also, the module placement, near the passenger side headlight
motor, is unprofessional looking. Although more work is involved, the
following instructions will provide a neat, reliable, and professional
installation. Please read through ALL the instructions first, before
beginning. I make no guarantee as to your results.
My background :
I am an Electrical Design Engineer, specializing in Power
for high reliability spacecraft applications. I am also a
dyed-in-the-wool car guy,
and have many years� experience with
automotive mechanical and electrical repair,
maintenance, and
restoration, both domestic and foreign. I owned a 1986 Z51 4+3 Corvette
for 11 years, and recently purchased a 2001 C5 6 speed Z51
Parts List
Hayden #3647 adjustable fan
controller module Pep Boys $39.99 stock #
grade wire, (not Radio Shack speaker wire!) stranded copper, AWG22 or 18,
about 12 feet
#xx machine nut, and 2 flat washers (for ground
#xx machine nut and flat washer (for 12V post on the side of the
eyelet crimp or solder wire terminal, xx ID dia
Velcro tape, with adhesive back. Radio Shack stock #
Rubbing alcohol
Shrink tubing insulation, Radio Shack #
silicone rubber sealant/adhesive
I located the fan
module in the underhood battery \”cool box\”, between the
box and the inner fender wall. This location was selected because of the
underhood temperatures, proximity to the Fusebox, and some
additional environmental
protection. The thermal sensor probe is
inserted through the radiator fins, located at the
extreme bottom
corner, driver�s side. This is the water outlet side of the
This represents the longest possible probe wire-length
needed, in case you want to experiment
with a different probe location
in the radiator. Use this suggested mounting information to
the correct wire lengths for the following steps. I unfortunately did not
the finished length of the wires of my installation, which
would make your installation easier.
I will give estimated wire
lengths, but check them for your particular installation!
Some C5
cooling system theory : The Corvette has a two speed, dual electric
radiator fan system,
under control of the PCM computer. The stock PCM
turns the fans ON at 225F, or if the AC freon
pressure rises (AC on).
The water thermostat, stock is about 190F, determines the MINIMUM
operating temp (that is the temp you see on the DIC when the car
is cruising, say at a steady 60MPH,
on a flat highway, for 15 minutes,
on a below 80F day). The radiator fan turn-on temperature
the MAXIMUM engine operating temperature (assuming the thermal capacity of
cooling system has not been exceeded). MAXIMUM is the temp you see
on the DIC when the car is
sitting in traffic for a while. This
installation retains the full stock functionality of the PCM fan control
(both speeds), which will ensure fan operation (at 225F) if the Hayden
controller or fuse fails.
The following connections will run the
dual radiator fans at the low speed. A different connection,
additional circuit complexity, can run the fans at the high speed, if
insufficient cooling
action / response time is observed. This fan
controller can only reduce the MAXIMUM engine
operating temperature. IF
a lower MINIMUM operating temperature is desired, this fan
should be used in conjunction with a lower temperature water
1) First, a few modifications you can do to the fan
module at your workbench : There is
one glaring design flaw with the
Hayden unit, which is easily correctable. I assume the
Corvette Vendor
versions have the same problem. The fuse is located in the wrong
on the Orange module (fan motor) wire. From basic electrical
safety design theory, a fuse
should always be located closest to the
power source, as a fuse only protects what is
\”downstream\” from it.
The proper fuse location is on the Red +12V wire. This will be
in step �B�.
A) There is an option at this first
step : If you want the fan to be able to run a few
moments after you
shut-down a hot engine, wire the Yellow wire as indicated below. That
how mine is wired. If you do not want this option, the Yellow wire
should be connected to
a source of \”+12V only when ignition ON\”,
from the fuse/relay panel. If I shut-down my car, after the fans were
already ON (from stop and go driving), the fans continue to run for
approx. 30 seconds, and then shut-down. This is an additional benefit, as
it slightly lowers the underhood \”heat-soak\” temperatures which occur
during every hot shut-down. I believe this will also extend the life of
the hoses and radiator plastic end-tank seals, as it lowers the pressure
surge associated with this \”heat-soak\” period. The downside of this
option is that if the fan module fails, the radiator fan may continue to
run on a parked car, totally discharging your battery
B) To
move the fuse, cut the Orange wire, with the fuse holder attached, right
where it exits
the fan module body. Trim the Red wire length, so that
when the fuse holder is spliced on,
the total length, from end of wire
to the module body, is about 8 inches. Trim the Yellow
wire to the same
length as the Red wire. Now, with solder and shrink tubing, splice one
of the Orange fuse-holder wire onto the Red and Yellow wire.
Solder/crimp on the Hayden
supplied eyelet terminal to the other Orange
fuseholder wire.
C) Locate the small corner reinforcement, directly
behind the battery, between the firewall
and the inner fender panel.
Trim the Black wire to reach from the module mounting location,
to the
firewall bolt (ground) of this reinforcement. Locate a nut and 2 flat
washers which will
fit onto the forward protruding bolt. Sorry,
don\’t know the size. Use solder/crimp and shrink tubing,
attach an
eyelet terminal (which will fit the ground bolt) to the end of the Black
D) Cut the two Gray twisted wires, between the fan module and
the thermal probe.
Cut it in the center of its length. Using a twisted
pair of wire, splice in, using solder
and shrink tubing, as an
extension between the probe and the module. Polarity of the Gray
is unimportant. Determine the length based on the routing from
the fan module location, to
the lower driver�s side of the radiator
core. I routed the sensor cable along the coolant
tank, closest to the
fender, then down the backside of the radiator/fan assembly, using
existing wire harness attachment clips as tie downs. Ramps or a
lift is required to get easy
access to the bottom backside of the
radiator core. The radiator is the REAR unit, the AC
condenser is the
FORWARD unit. The cable is probably about 6 feet long. Try a trial
for now, to determine the cable length, but do not yet insert
the probe into the radiator
core fins. The twisted pair wire is
necessary to reduce electrical noise-pickup on the sensor
wires. You
can make twisted pair wire with an electric drill and a bench vise. Cut an
extra long
(1.5 X) pair of wire, clamp one end in the vise, and the
other in the drill chuck. Pull taut, and
use the drill to twist up a
neat pair. Then trim to desired length.
E) Optional : If you want
to install a manual fan override switch, to turn it on at any
extend the Green wire, with solder and shrink tubing, to pass
through the firewall, and connect
to a switch that provides +12V fused
power. I intend to do this, but have not yet. If you do
not want this
option, cut the Green wire off, about 2 inches from the module body
you change your mind, later). Insulate the cut end of this
wire with a tight fitting piece of
shrink tubing.
F) Put a small
blob of RTV on the exposed end of the cut-off Orange wire (at the module
and at any shrink-tubing joints where water might get in. I also
put some on the crimped end
of the sensor probe aluminum tube, and its
shrink tube joints. Let the RTV cure, overnight,
to eliminate a
potential handling mess during the next step.
2) Now for
the underhood installation :
A) RECORD your radio presets and
security (radio Theft-Lock) codes. See owner�s manual for
B) Disconnect the black (ground) terminal from the
battery. Make sure it cannot \”flop\” back and
contact the battery
C) Remove the top cover of the underhood fuse/relay box.
From the guide inside the cover,
locate Mini-Relay # 45 (Cool Fan 1).
Mine is grey and square, made by Siemans.
D) Using a flatblade
screwdriver, release the 4 retaining clips that hold the fuse/relay
to the bottom box/housing, while pulling straight up on the
panel. Some upward force needs to be
exerted, due to the many stiff
wires on the back side. Carefully pull the panel up, about 3 to 4
and slightly rotate it, fuse side towards the battery. Use a
mirror and a flashlight, locate the large white
plug located directly
below relay #45. The white plug terminals are identified with small row
and column
numbers and letters, molded into the edge of the white
plastic. Locate the thick baby blue wire, directly
below relay #45, at
location 3B. About 2 inches from the white plastic plug, strip back the
insulation, around the entire circumference of the wire, about 1/8 to 1/4
inch in length. Do not cut the copper wire, just a ring of insulation. Tin
the exposed copper with a medium to high wattage soldering iron.
Place the fan module in the corner, between the fuse/relay box, and the
inner fender wall. Mount it to the
inner fender wall using Velcro tape
on the side of the module case. Use some rubbing alcohol on the module
body and fender wall to ensure that the Velcro strips will adhere well.
This allows you to pull it off to adjust the temperature kick-in control
and then re-attach the module upside down (flat black side up, wires
down), so that water won\’t run into the unit. It also looks neater.
F) Snake the Blue module wire into the bottom of the fuse/relay
bottom box/housing, where an existing
harness enters. Trim to a
reasonable length, then strip, form into a hook, and tin the copper
Hook this wire around the thick baby blue wire stripped and tinned
in step D, and solder together.
Insulate the connection with electrical
tape, and/or a blob of RTV.
G) Push the fuse/relay panel back down
onto the lower box/housing, making sure the 4 clips engage.
The panel
will move a little, even if the clips are all engaged.
H) Connect
the Black ground wire to the corner reinforcement stud, using two
additional flat washers and nut, over the existing nut. Put on the washer,
then the ground lug, then a washer, then the nut.
I) Connect the
fused Orange wire eyelet lug to the 12V battery post, on the side of the
fuse/relay box, using an additional flat washer and nut, over the existing
nut. Sorry, don\’t know the hardware size. Orient the lug so that the
fuse panel cover fits on, over the +12V post , with the new lug attached.
Then tighten the nut. Reinstall the fuse panel cover. Verify that there is
a 25 Amp fuse in the fan module fuseholder.
J) Route the thermal
probe cable forward, past the coolant tank (along tank side closest to
fender), and down the backside of the radiator/cooling fan assembly. Raise
the car for underneath access. Use a small
flatblade screwdriver to
unlatch the existing fan harness tie-down clips, and route the sensor
cable through them.
Per the Hayden instructions, and probe mounting
hardware, carefully insert the thermal probe into the small
fins of the
radiator core, pushing the probe in from the rear, wires exiting towards
the back. I placed the probe in the lowest drivers-side corner of the
radiator core, next to the end-tank, where there is an opening in the fan
shroud. This is the water outlet side of the radiator, and I thought the
best place for the probe. The Hayden instructions imply to install the
probe on the coolant inlet side (closest to the water thermostat) of the
radiator (passenger side), but I don\’t agree with that.
If you
feel uncomfortable about poking through the fins, you could RTV the probe
to the underside of the U-shaped aluminum channel of the lower core
support. Orient the probe so it�s length runs along the length of the core
support. Apply upwards pressure to make sure the probe body remains in
intimate thermal contact with the support, until the RTV cures.
are of course free to experiment, which may alter the length of time the
fan runs, and change of engine
temperature as the fan cycles ON and
OFF. Any opinions or experience with the probe placement would be
Verify that all wires are secured, and away from any
moving or hot engine or suspension parts.
Make sure the sensor wire
does not hang too low beneath the car !
K) Rotate the fan module
adjustment screw fully CCW, so that the fan is OFF until the engine warms
Do not force the plastic adjustment screw past its stops, it can be
easily damaged. It does NOT rotate a full
L) Reconnect
the battery ground cable, reset your radio, and start her up. Let it idle,
with the hood open,
while watching the engine temperature display on
the DIC. Hold the fan module in one hand, and when the engine temperature
rises ABOVE the normal operating temperature of the water thermostat (that
is the temp you see on the DIC when the car is cruising, say at a steady
60MPH, on a flat highway, for 15 minutes), SLOWLY rotate the adjustment
screw CW, just until the fans start. You will need to feel the fan module
relay click, as the radiator fans are rather quiet on the low speed. I set
my fans to come on when the DIC display had increased to about 197F. My C5
water thermostat temperature is about 193F. This adjustment is very
sensitive to the amount of rotation of the screw, and may have to be
repeated to get it just right. Too high a turn-on temp setting will run
the engine hotter (maximum) than desired, too low a setting will result in
extended unnecessary operation of the cooling fans. When set properly, the
fans should come on before 200F, and shut off shortly after the engine
temperature has dropped to the minimum water thermostat temperature. The
actual engine temp may peak slightly above 200F, until the radiator fans
can \”catch-up\”, and lower the temps to the shut-off point.