I know this has been talked about before and I have searched the archives but can't seem to find a clear answer.

Is there a way to setup a manual fan switch that will turn the fans on in high speed mode without causing problems for the normal PCM controlled mode?

I know they can be programmed and have done this, but I want a manual switch for certain situations (like in the staging lanes) and don't want to reflash the PCM every time I want the fans on earlier.

I found this schematic if someone would like to reference it in an explanation.
http://www.vetteguru.com/misc/fans.gif
Any help would be greatly appreciated.



[Modified by QuickSilver2002, 10:41 PM 6/23/2003]

 

:lurk:

 

Yes I have all the instructions for a manual fan switch. I get random emails about once a month for the mod. Works like a champ. I did it about 2+ years ago. I am just passing it along. :D

anybody who wants the manual fan switch instructions email me at intel55@aol.com and you shall have this $10 (in parts)mod

:D :D :cheers: :smash:

OH yeah MAKE SURE YOU PUT IN THE SUBJECT LINE: FAN MOD!!!!!

thanks :D


[Modified by intel55, 2:13 AM 6/24/2003]

 

sent 10 of ya the instructions. Easy mod. Cheap :D
:flag

 

Intel55, thanks for the info.

I'm a little confused about how the mod in the email works. Does it allow you to keep the PCM controlling the fans when the switch is not on?

 

No, the high speed fan will only work manually. If you only want to use it manually once in awhile you can just replace the original fan relay and you are good to go (basically pull out those two wires and push them to the side). The low speed fan will still run off the pcm. :cheers:

 

humm, I still don't think the mod shown in the email could run the fans in high speed mode. It looks to me like it would just turn the right fan on in high mode (I could be missing something).

I'm not an EE of any sort, but it looks like there would be a pretty simple way to accomplish what I want (now that I have studied the schematic for quite a while).

It appears that all three relays (coolfan1,coolfan2,coolfan3) need to be activated for the fans to be in high speed mode (both wired to a 12v source). In low speed mode, coolfan 1 is activated and the fans are both on, but wired in series. The pcm grounds both the low and high speed wires to accomplish high speed mode. The low wire activates coolfan1 while the high speed wire activates coolfan2 and coolfan3.

I think it would be pretty simple to find the fan control wires coming from the PCM (DK GRN-42 and DK BLUE-33) and setup 2 little relays to ground them when a manual switch is on.

I can't see how this would cause any problems, but I'll run it by an EE friend of mine just to make sure before I try it. I'll post pics and instructions when done.



[Modified by QuickSilver2002, 12:31 AM 6/25/2003]

 

:lurk:

 

The setup only runs the fan that sits directly over the coolant line at high. THis is really the only one needed. I did this primarily to cool the engine while sitting the staging lanes. I could turn off the car, take the keys and let the fan cool things down. :cheers:

 

Cool, that makes sense.

I have a slightly different purpose. I have my intercooler mounted directly in front of the radiator and I want to pull as much air as possible across it and drop the coolant temp down as much as possible before I hit the tree. I'm also going to rig up something that will spray the intercooler with a fine mist.

I'll keep you guys posted on how my fan switch mod works out.

 

:cheers: Thanks

 

I got my fan switch wired up tonight and it seems to work perfectly. I ended up doing two switches, so I could run low or high speed on demand. The total cost was about $15, but you could do it for about 2$ if you did not want lighted switches. This mod can actually run both fans in the high speed mode, which gives you twice the CFM compared to the other methods I've seen that only run one fan in high speed mode. The switches simply override what the PCM is demanding when they are on. They have no impact on what the PCM would normally do if you have them switched off.

It was so simple that I can't believe more people have not done it.

I'll probably do a more complete write-up with pics later in the week, but here are the basic instructions.

Look at this schematic http://www.vetteguru.com/misc/fans.gif
Look at the bottom left of the diagram where it has the dashed line around the PCM and the two wires (DK green and DK blue) labeled. You will basically be splicing into these wires and adding in a manual switch that runs each wire to ground. Grounding the green wire only will turn both fans on in low speed mode (wired in serial). Grounding the blue wire will turn the right fan on in high speed mode. Grounding both wires will turn on both fans in high speed mode. The ignition has to be on for the blue wire to have any impact, but the low speed fans can run without the ignition in the on position.

Here are the basic instructions
1. Take off the front passenger wheel and wheel well panel that protects the PCM.

2. Crawl under the car and you will see two long connectors that are bolted up to the PCM. Unbolt both connectors and pull them away from the PCM. You will see that one is blue and one is red (on the inside).

3. Page 6-618 of the 2002 manual has the pin outs for these connectors labeled in detail. On the Blue connector you are looking for pin 42 which is the dark green wire (low speed). It is the 2nd pin from the left on the top row with the tabs on the connector oriented upward. The wire is somewhat hard to get to (since it comes from the end of the connector and not from up top) and you will probably have to cut away some of the shielding tape to see it. The space is tight, but it is not bad if you use a tap connector to splice into it (they sell these at Home Depot - look for something close to 30 AWG). I think there was another dk green wire on this connector, so make sure you get the right one.

4. The Red connector contains the high speed wire (dk blue). It is pin 33 and is on the bottom row 8th from the left with the tabs facing up. It is also a little hard to get to for the same reasons, but I think there is only one wire this color to worry about.

5. After you have spliced into these wires you can do whatever you would like to setup a switch that will ground them. I ended up using two relays and some lighted switches mounted in my ash tray area, but you could go as simple as some alligator clips in the batt box. Pretty much anything would work and there are several different ways to do it. Just remember you don't want to switch them to a power (+) source. You are simply switching them to ground (-).



[Modified by QuickSilver2002, 10:19 AM 7/2/2003]

 

Update:

This does cause p0480 and p0481 (fan relay circut) to get thrown when the PCM tries to turn the fans on (but they are already manually overidden). This is a rare situation, but it can happen. These can be easily disabled in ls1edit to keep the check engine light off. Other than the light coming on, it seems to cause no harm.

 

Would installing a few diodes help stop the manual ground signal from getting back to the PCM?

 

Yep, MANNY is right. That would have been much easier. I've taped the PCM wires for other things in the past and just had a tendency to head in that same direction. I also knew I would not screw up anything with the approach I took.

 

In looking through the trouble codes as well as the trouble shooting procedure for engine over heating, it appears that the PCM is only aware of whether the fan relays are operating as they should and has no idea if the fan motors themselves are working.

If you use a relay similar to the stock relay #44 (a two output relay) between the power wire to the fan motor and the fan motor itself then when the manual fan switch is off the PCM would control the fan and when the switch is on the fan motor would be on regardless of what the PCM wants to do.

As the stock relays would continue to function as commanded by the PCM, no codes would be thrown :cheers:


[Modified by SFVetteman, 10:08 PM 7/4/2003]

 

Just run a hot lead from the bat pos term to the right fan white wire, fuse it and switch it at the batt and you are done. Has works on 3 vettes so far no problem.

 

That would work with the right fan only, since the grounding of the left is controlled by the #44 relay…
---Manny

According to the diagram referenced in the original post the left fan is controlled by the #45 relay. Moreover, the fans are not grounded by the relays they are powered by them. The other terminal of the fan motor goes to ground. Most importantly, my method bypasses the stock relays and PCM when you want high-speed operation of one or alternatively both fans without the PCM throwing codes.

Let me try to explain this a little differently so you can understand.

1) You will need a new relay similar in design to the #44 relay, toggle switch, some wire and an inline 30-amp fuse. 2) Remove the blue 409 wire from the left fan motor. 3) Connect the unswitched side of the new relay to the left fan motor. 4) Connect the switched, normally open terminal of the new relay to a new wire with a 30-amp fuse going to the battery or other 12-volt source. 5) Connect the other switched normally closed terminal to the blue 409 wire. 6) Connect a wire from one of the relay coil terminals to the wire going to the battery or other 12-volt source. 7) Connect a wire from the other terminal of the new relay coil to one terminal of a dash-mounted switch. 8) Connect a wire from the other terminal of the dash-mounted switch to ground.

Now with the flip of a switch you have a choice of normal fan operation using the stock relays and PCM or manual high-speed operation of the left fan motor with no codes. The procedure for the right fan motor is the same except that the white 504 wire instead of the blue 409 wire controls the right fan motor. If you want to have the ability for both fans to run manually at high-speed, you will need one new relay for each fan.

 

:iagree: As long as you use a switch that can handle the current. I prefer to switch it with a relay but that's really a personal thing :cheers:

 

Yep, all depends on how big of a deal you want to make it, fuses on the big side work well for me. I like the KISS method. :yesnod: