Fan Switch Mod ???????????

[turbota]

Has anyone done the fan switch mod as described by TTA 1456 (member)? I finally got around to doing it (after a year) and found that if I had the ignition key OFF and the fan "jumper" switch , which runs both fans off of the temperature switch, turned off, then turned the jumper switch on, then the ignition switch off - - the high speed fan (rt,. side) ran forever?. This happened while the engine was "stone cold" (sitting for more that a month) and I was wondering if anyone was having this problem ??? Any help wouln be welcomed. Turbota
P.S. This mod should really help while in city traffic (if i could make it work.....)

 

[Gokou]

I did the quickie write up on that mod, and I have no such trouble with my car.

You probably have a sticky fan delay relay. Common problem. You can completely disconnect the connector from the delay relay; the only functionality you will lose is that if you should ever happen to turn your car off above 226F the fan won't run for 10 minutes after shut down.

If you want to rule the delay relay out, simply disconnect it and try the procedure you described again.

Also, my suggestion is not to play with the jumper switch and ignition switch. Just leave it on (so both fans turn on simulataneously) and then you shouldn't have any problems.

 

[GNandTTA]

so both fans turn on simulataneously

Not so sure that is a good idea. Friend of mine did that on his IROC and after daily driving for a while his alternator died. May be a coincidence, don't know. The fan motors current draw on initial startup is much more than once it is running. Doubling that might be too much of an instantanious draw. The factory system NEVER turns both on at the same time. I have LED's in my dash to show when the fans are running. At least on my car with neither fan on, if I turn the AC on the drivers side starts first and about a second later the pass. side starts. They NEVER start simulataneously even when the ECM wants them both to be running.

I have a switch wired up to turn both fans on manually. I only use it for after cooling with the engine off. I've had it wired for well over 10 years with zero problems. So the only potential problem could be damaging the alternator diodes.

 

[Gokou]

Originally posted by GNandTTA
Not so sure that is a good idea. Friend of mine did that on his IROC and after daily driving for a while his alternator died.

That is a valid concern, as the initial amp draw on turn-on would be fairly high. However, the battery should supply enough extra amperage to make up for it.

The fans can turn on simultaneously normally, but it would have to be under very specific circumstances-- i.e. the ECM switches one fan on due to engine temp and at the exact time the A/C pressure switch kicks the other fan on. Probability is against that happening however.

I think your friends alternator dying is a coincidence. The factory would have to build the wiring harnesses and electrical systems to support both fans turning on simulatenously, because it can in fact happen. If they didn't, they are poor engineers for not taking into account a possible occurance in everyday driving.

Keep in mind that the ECM can't signal the passenger side (high speed) fan by itself. The passenger side fan can only be triggered by the normal A/C pressure switch (150 psi) or it can be turned on in conjunction with the 208F temp switch in the intake if the VSS is reading under 45mph. The ECM only has direct control of the driver's side (low speed) fan; in addition to ECM control of the driver's fan it can also be triggered by the A/C high pressure switch (275 psi) and also by the delay relay after key off if the engine temp at shutdown exceeds 226F as signalled by another temp switch in the intake.

 

[GNandTTA]

That is a valid concern, as the initial amp draw on turn-on would be fairly high. However, the battery should supply enough extra amperage to make up for it.

The problem is that because the alternator puts out more voltage than the battery, all of the load falls on the alternator first. With the engine off it is no problem.

The factory would have to build the wiring harnesses and electrical systems to support both fans turning on simulatenously, because it can in fact happen. If they didn't, they are poor engineers for not taking into account a possible occurance in everyday driving.

Once in a while is no problem. Kind of like detonation, a few times can be absorbed. Actually if that did happen you best go out and buy a lottery ticket because the odds are pretty slim. However, I think it could be a problem if it is happening all the time.