c4speed

I bought a manual cooling fan switch from one of the big vendors that states it is for 84-93, I asked if it would work on my 95, they said yes. Directions only tell how to wire for 2 fan relays my 95 has three. It has 2 wires one each for two relays and a ground wire to screw to ground. Can I make this work ?

pcolt94

Hears the situation. Are you aware of how your fans work. The three relay combination enables the fans to both run at the same time in either low speed or high speed. This is different than the earlier years where they run independently.

Your fans run at low speed when you either turn on the A/C, or when the temp reaches 228*. They will go into high speed at 239* and then cycle to the lower speed about 10* lower.

So connecting the relays to run at the lower speed is a waste of time since they are on with the A/C already.

So it makes sense to make the connections so that the fans will run at the high speed setting with the manual switch.

Is this what you want to do, to run at the high speed configuration.

c4speed

Thank you for your response, yes this is what I want to do. The reason I am doing this is when I go to the drag strip on hot summer nights waiting in line to race the temps will reach as high as 233 so if I could turn the fans on high like you said this would help a lot. should I tap into #1 and #2 or just # 3 relay and what color wire, they only tell the color for up to a 93.

pcolt94

There are 2 control lines for the selection of the fans going into low or high speed. Both of the wires have to be grounded for the high speed operation.

Off of relay 1 there is a dark green wire that goes to PCM pin A11. The other wire is a dark blue wire from relay 2 & 3 that goes the PCM pin A10. These both need to be grounded for the high speed operation.

I would not connect the blue and green wire together and then the ground them. To do it right and so all other aspects of the fan operation work normally, you need to use a double pull switch not a single poll. A DPDT switch would be just fine or DPST.

One wire goes to each section (poll) of the switch and the other side of the switch goes to ground. These ground points can be connected together and grounded with a single wire. This will keep each relay (solenoid) circuit separate until the switch is closed. Then the fans will run at high speed until it is turned off.

Any questions, if you're not sure or clear…….ASK.

c4speed

PM sent

Rocket-J

That is great info for any of us.
I would love to turn my fans on manual as soon as I pull onto a track and not turn them off until I get below 200 degrees. Why wait until
230+? A switch should be available at any Radio Shack or auto parts house. Is it safe to assume those pin numbers are good for all 1994-1996 C4's?
Thank you

c4speed

I would not wait until 230+, if I get the switch working I will get down to 200 and pick up a 1/10 or so.

pcolt94

This information is only good for 95 & 96. The 94 is different since fans operate separately with each having its own relay. For street operation it's only necessary to turn on the secondary fan. (Because the primary fan comes on with the A/C). This is what I have on my car. When the temp gets above 210 or so I will turn it on. Depending on outside air temp, and how long you in traffic will depend when I turn the switch off. Here is the info from another thread I wrote up back when.

The 94 uses 2 relays and 95-96 uses the 3 relay system.

Hears how I did it. Here are some older pictures and the drawing for the wiring. There is no need to connect to the drivers side fan since it comes on with the A/C anyway.


*** Use #473 wire




*** Relay wire connection shown



*** Ground wire and relay wire connection shown


Connect one wire from the switch to the dark blue wire #473. No need to cut wire, just skin back insulation and wrap around. This wire has 12 volts on it and is the return or low side of the relay coil. The other terminal of the relay coil has the 12 volts supplied from the fuse. The other wire from the switch goes to ground.

When the switch is closed, the coil of the relay will be energized and close the relay contacts starting the fan. This is the same process that the PCM does by grounding the #473 wire.

I elected to run the ground lead to a convenient point under the hood near the fan relay. I ran my wires into the car and hid it under the speaker enclosure to under the seat where all I have to do is to reach down and flip the switch on or off. Works great, been doing it for years.

Any kind of toggle switch will work and I used an encapsulated wire, 2 wires in one cable.


***You can connect another switch to wire 335 (green wire) and control the primary fan and never turn the A/C on to run the primary fan.

rodj

Why use a manual switch?
http://www.racerpartswholesale.com/p...n_Accessories2

If you only want lower temps at the track, install a manual switch under the hood on the wire to above switch so it only operates at the lower temp when you want it to

Red Rocket

Use the manual switch on my 94. In the staging lanes it usually drops 5-8 degrees with the motor not running and the ignition on for about 2 minutes before moving forward. Turn off the fan after burnout and before launch. 170-175 temp in Texas heat.

pcolt94

Am I missing something. The ECM or PCM gets it input from the sensor in the water pump (ECT). Then the ECM/PCM make the decision when and what to turn on fans.

I think that part might work on the ealier vette with a different fan system. Where wound screw it in and what would it connect to?

Does this make sense.

rodj

Correct ,as programmed in the ECM ; approx 230F

Makes no difference if you do as you stated above and only connect to one fan system.
To run both fans would require extra relays to maintain isolation of fans from each other

Installs into any coolant passage ; LT1 has a blank plug in drv side head
Is wired in exactly the same as a manual switch except you don't have to remember to turn it on or off.

pcolt94

Posting this picture for switch connection as per IM with c4speed for a 95 & 96.

It is probably easier to find a double poll double throw switch than a double poll single throw switch. With the DPDT switch, you would only use 4 terminals leaving 2 un-used.

Two terminals of each switch get connected together and grounded (I would use the center terminals on a DPDT). The other terminals of each switch go to one each wire connection. It does not matter which wire (green or blue) goes to the remaining 2 terminals.

Most small toggle switches you find will handle 3 amps which is plenty to handle this circuit. The draw is under 1/2 amp.

c4speed

Thank you pcolt94

Luweegy

I bought one of these from HyperTech for my 93.My sensor at the water pump has 2 wires instead of one.Is the sensor at the waterpump the one I want to change?

pcolt94

Do not mess with the wires on the sensor in the water pump. It is for the digital temp gauge and temp input to the ECM.
That input also tells the ECM when to turn on the fans. Is also does several other things to run the engine correctly


The sensor with 1 wire is the one in the head on the passenger side which is the sensor for the analog temperature gauge.

Cavi

why not just use a adjustable thermostat kit like this one:
http://www.summitracing.com/parts/PRF-30104/
I do like the idea of the manual switch for autox days, but for traffic, I would perfer not to have to remember to flip the switch.
Also, does the 94 have 2 speed fans or just the newer ones with 3 relays?

pcolt94

Wow - $87 for that stuff. I wouldn't even try to install it on somebody else's car.

Sorry - Just my opinion, whatever floats your boat.

The 95 and 96 use the 3 relays and have the two speed fan configuration.

94 uses (circuit in post 8) 2 fans, one speed, each controlled by its dedicated relay and relays controlled by PCM.

rodj

So you splice in a manual switch.
ECM runs fan as programmed and you turn on fan(s) manually at track.
Problem solved

leesvet

Its not difficult. A wiring diagram tells you where to find the correct wire/place to interrupt the circuit and jump in.

you simply complete the ground path instead of waiting for a sensor or relay to do that. Fan ON...no biggie.

NEVER attempt to run hot wires, jump hot wires or switch the existing hot wires. Work with GROUNDS ONLY just like the ECM does.

There are many means of doing this...

different temp sensors that complete ground at a lower temp.
add a switch.
change chip program.
jump grnd @ the relay.
tap into ground path and run pair of wires into cabin and mount or hide switch somewhere. One side to a frame bolt other side to ground path @ relay.
If done correctly it works as normal and there is min butchery of the harness.


FWIW..
I have used switches, temp probes, sensors, and all means of getting fans to run sooner, earlier and/or longer. It ALL amounts to junking up a fragile electrical system and should be avoided for many reasons, the biggest is that these motors are designed to run hotter than we are comfortable with. Unless you "tune" the motor to run cooler with the appropiate fuel and air, you;re doing damage slowly as you run rich and contaminate the cats and engine oil with hydrocarbonsa and worse, moisture that cannot boil away. Thats the biggie, if the engine never gets to 200 (in that area) and stays there for a while any mointure in the oil stays and does its damage.
The BIG reason to drop the temps for most follks is performance. The car seems to run better at 190 than it does at 220. Probably does. You can tune it to do that. The most appropiate reason to drop op temps is safety margin. There is dam little time to react to a blown rad hose at 225 degrees if you are stuck in the middle lane of the freeway in rush hour. Bad things happen quick.
if you;re norm is down there at 190-200 you get a few more valuable seconds of time to shut down, move over, turn off...whatever.
But, to manage op temps properly takes more than $3 worth of switch or wire. It takes a radiator that will manage heat better, give you stable temps without spikes and fan management/control. Some tuning, and a water pump that actually moves water when there is heat exchange (fan running or traveling @ speed).
A switch is a start but for that to work you have to change T-stats, then you;ll soon see that this only buys you a few more minutes in many cases. You have to do more to get that level of control over operating temps.

And it still comes down to a 4" piece of rubber hidden under your a/c compressor bracket that can ruin your day when you;re least prepared....