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Old May 3rd, 07, 01:53 PM   #1 (permalink)
 
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Manual Switch for cooling fans

Just put a new rad in the beast (1994 Z28) and now Im not liking the fan turning on at 215 degrees. Which wire do I need to splice into to run the fans off a switch with constant power.....In a nutshell, Looking to have the fans turn on manually....even if the car is OFF...thanx
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Old May 3rd, 07, 04:11 PM   #2 (permalink)
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Re: Manual Switch for cooling fans

those cars were meant to run in that temp range.
not sure which wire, but if you find the fan relay you can go from there.
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Old May 4th, 07, 07:32 PM   #3 (permalink)
 
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Re: Manual Switch for cooling fans

the computer will make the car run fat at less than operating temp...will possibly call a code for bad coolant temp sensor also...the fans are actually supposed to come on at 224-227 degrees in gm apps...but as stated above, if you wanted to make an "over-ride" switch, find the relay on the firewall, and tap into the sensor wire...all you`ll need to do is add a ground to the wire, as that is all the computer does to close the relay...the relay has power whenever the key is on i believe...
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Old Jun 17th, 07, 03:19 PM   #4 (permalink)
 
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Re: Manual Switch for cooling fans

neither of my '94 Z28s run at that temp
add a 160 thermostat and kustomwerkers advice sounds right on to me
the relay can be jumped with a short wire to keep 1 fan running (I do this at the track)

the fans can be turned on sooner by reprogramming the pcm fwiw
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Old Jun 17th, 07, 03:55 PM   #5 (permalink)
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Re: Manual Switch for cooling fans

Just went thru some of this on the vette. The stock thermostat is 195 degrees. The primary fan comes on at 220, the secondary at 235. Turning the A/C on runs them both regardless of engine temp.

Normal temp for an LT1 is 200-220 degrees, over 235 is hot.

I'm not an LT1 guru yet by any means, just got the vette 2 weeks ago... Best way to turn the fans on sooner is to get a copy of RT_Tuner from tunercat, and a cable, and hook your laptop up, make the change, and reflash the chip.

You are lucky, your 94 uses a flashrom, my 93 uses an eprom and it's not so easy to change.

If you insist on the switch, just find the relays. They have the internal schematic printed on the in whte. The relay coil is fed 12 volts on one lead, and the other coil lead is grounded by the computer to turn the fans on.

You can do 2 things here. You can connect the ground side wires together. This will turn both fans on at 220, and cool things off in a hurry. You can also run your switch from this wire. Ground the other temrinal of the switch.

Make sure both fans are running when the air is on, they should be.

BTW, I had the rad out of the vette yesterday, gawd what a nasty job. Core was filthy, packed with crap. She'd get over 250 in traffic with the A/C on. Cool as a cucumber now.



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Old Jun 17th, 07, 10:01 PM   #6 (permalink)
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Re: Manual Switch for cooling fans

SLP makes a fan switch for around $60....
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Old Jun 18th, 07, 04:02 AM   #7 (permalink)
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Re: Manual Switch for cooling fans

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Originally Posted by JimM View Post
You can do 2 things here. You can connect the ground side wires together. This will turn both fans on at 220, and cool things off in a hurry. You can also run your switch from this wire. Ground the other temrinal of the switch.
I wouldn't think the 220*F relay driver of the PCM could handle twice the current to run both relays in parallel. The resistive load has been cut in half.

By placing a body ground on the return wire to the PCM, wouldn't this be commanding the relays to be ON all the time? My thoughts are the relay has coil has two terminals, one with battery voltage all the time, the other terminal is connected to the PCM driver. When not commanded ON, battery voltage is at both teminals. Placing a ground on the PCM side would activate the fan all the time.

I'm thinking when the PCM commands the fan(s) ON, the PCM wire goes low, 0.5 vdc, and relay energizes under normal wiring. If the wire is grounded, and the relay driver turns on, and it is connected to ground, wouldn't this action eventually break the relay driver? Max current for the relay drvr?

Looking for an education here on LT-1 control for future use, thanks.
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Old Jun 18th, 07, 04:21 AM   #8 (permalink)
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Re: Manual Switch for cooling fans

Manually grounding those wires won't hurt the relay drivers. They are intended to pul 12v down to ground thru the relay coils, pulling ground down to ground... they'd be doing nothing, no current.

Yes it's true tieing them together would double the load on the main fan driver. I haven't tried it myself, but over in the C4 section of the corvetteforum, it's a pretty common thing to do.

Also do some double checking on the flashrom thing, just because vette's went to that in 94 doesn't mean (for sure) that Camaro's did.



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