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4/4/14 3:22pm - Original Message: 'Manual Fan Control'
cco
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, - Canada

Vette(s):
1994 convertible, Polo Green 2 1G1YY32P9R5114269 ---------- 2006 Monterey Red Vert 1G1YY36U665125919----

Joined: 8/16/2013
Posts: 191

My C4 goes in on Monday for a manual fan control (amongst other things)

For those who have done this is there a location for the switch that would be optimal?

Obviously near the d/s seat to make it accessible, maybe near the steering column or off to the side near the hood release.

Any suggestions? 


I'm also assuming that the cooling system will function as normal with the fan(s) cutting in and out as normal, unless I override with the manual control on.

If the fan control is left on, is the circuit cut by the ignition being shut off, or should it be wired directly to the battery for control when the ignition is off?


Thanks,

 Colin.



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4/4/14 10:02pm - Reply: 'Re: Manual Fan Control'
Adams' Apple
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Duncanville, TX - USA

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1985 Coupe-L98/Auto,Bright Red/Carmine. 1974 Coupe-L48/4speed, Medium Red Metallic/Black Deluxe.

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Not sure how you're going to be able to wire up a manual switch in the circuit without it being "seen" by the PCM, and setting a code. Also, sometimes wiring up one like that can cause a backfeed into the circuit, and cause more problems.
Why do you need to control the fan(s) manually, anyway? You scared of that 235* coolant temp? LOL

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4/5/14 11:12am - Reply: 'Re: Manual Fan Control'
396c4
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96 Vette with extensive list of mods, many one-off and custom.

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You're right about setting a code. I wired switched power to the control side of the relays and the ECM sets a code because it sees voltage when it shouldn't. It's OK as long as the ignition is "off" but easy to forget. I think the only way is to power the fans from separate relay(s) "Low speed" is sufficient for extended cool down but it becomes tricky to wire the fans in series to create the "low speed" operation without wiring issues for normal operation. Wiring a single fan on high speed from a single relay, on the other hand is relatively simple.

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4/5/14 1:51pm - Reply: 'Re: Manual Fan Control'
djsroknrol
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Altus, OK - USA

Vette(s):
1984 L83/MD8 coupe

Joined: 2/7/2011
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Don't you mean "early on" Colin?....The fans come on too late for some folks and they wire an override to the relay.




|UPDATED|4/5/2014 11:51:22 AM (AZT)|/UPDATED|


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4/5/14 2:35pm - Reply: 'Re: Manual Fan Control'
cco
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1994 convertible, Polo Green 2 1G1YY32P9R5114269 ---------- 2006 Monterey Red Vert 1G1YY36U665125919----

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Posts: 191
djsroknrol said: Don't you mean "early on" Colin?....The fans come on too late for some folks and they wire an override to the relay.







Yes the fans do come on late (for me) .... and I was hoping for a little manual control.


Sounds to me like a PITA if it generates a code. Have to see what the installer has in mind. Apparently he's done a few of these without issues.


A little beyond being "scared", Joel, No spring chicken any more [smile] -- but the high temps of the C4's are an eye opener for sure and I would prefer more control over that. But not at the expense of 'codes'.


I'll holler after Monday's day at the shop exactly what transpires.


Thanks for the input guys.


Cheers

Colin.



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4/5/14 2:37pm - Reply: 'Re: Manual Fan Control'
cco
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1994 convertible, Polo Green 2 1G1YY32P9R5114269 ---------- 2006 Monterey Red Vert 1G1YY36U665125919----

Joined: 8/16/2013
Posts: 191
396c4 said: You're right about setting a code. I wired switched power to the control side of the relays and the ECM sets a code because it sees voltage when it shouldn't. It's OK as long as the ignition is "off" but easy to forget. I think the only way is to power the fans from separate relay(s) "Low speed" is sufficient for extended cool down but it becomes tricky to wire the fans in series to create the "low speed" operation without wiring issues for normal operation. Wiring a single fan on high speed from a single relay, on the other hand is relatively simple.



That may be the way to go then, 396 -- and may even be what the installer has in mind.

I'll be checking that out on Monday.

Thanks,

C.



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7/7/14 6:46pm - Reply: 'Re: Manual Fan Control'
davep85c4
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...

|UPDATED|7/7/2014 4:46:02 PM (AZT)|/UPDATED|


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4/6/14 7:05am - Reply: 'Re: Manual Fan Control'
cco
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1994 convertible, Polo Green 2 1G1YY32P9R5114269 ---------- 2006 Monterey Red Vert 1G1YY36U665125919----

Joined: 8/16/2013
Posts: 191

Hi Dave -- your explanation is reassuring and sounds like the job is do-able. As I mentioned b4 the installer has done some C4's b4 and apparently knows what's up......


yes I've cleaned out the debris from in front of the radiator and from in front of the condenser.

There was some but not a lot of buildup like I've read about with other C4's. Airflow at the front is on my list of regular maintenance since cooling is so critical on our cars.


About being a "hybrid" --  Is there an OBD1 code-reader available?  I'm used to having a reader available to me but understand that this is an odd circumstance and that code reading is not so straightforward.

I know there's another way of reading codes thru the ALDL and have read about that -- Not done that method b4 and would feel much more comfortable with a reader if one is available.


Thanks, Dave, for taking the time to post -- You've set my mind to rest over this install.

I very much appreciate all the help available here with a very knowledgeable C4 crowd.

You guys are the best.


Cheers,

 Colin




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4/6/14 7:47am - Reply: 'Re: Manual Fan Control'
396c4
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Don't forget the thermostat still has primary temperature control and a high temp t'stat is going hold the temp no matter what the fans are doing. Interestingly, NASCAR engines are running much hotter than the "old days" and I understand they are using very high pressure caps to keep it from boiling. Some of it no doubt is to deal with drafting but a little higher doesn't seem to be a bad thing.

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4/6/14 12:23pm - Reply: 'Re: Manual Fan Control'
cco
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1994 convertible, Polo Green 2 1G1YY32P9R5114269 ---------- 2006 Monterey Red Vert 1G1YY36U665125919----

Joined: 8/16/2013
Posts: 191
396c4 said: Don't forget the thermostat still has primary temperature control and a high temp t'stat is going hold the temp no matter what the fans are doing. Interestingly, NASCAR engines are running much hotter than the "old days" and I understand they are using very high pressure caps to keep it from boiling. Some of it no doubt is to deal with drafting but a little higher doesn't seem to be a bad thing.



Right on 396 -- The stat was one of my first 'mods' -- putting in a 180.  I've heard that sometimes these 'stats can malfunction closed which will cause high temps .. I'm wondering what the best way is to check that the stat is functioning properly.

 The best time probably would have been b4 its install to watch it open in 180-185* water.


Can you watch the digital temp readout and garner enough info as to whether the stat opens or not?


ON a side note, the more I hear about these LT1 engines the more I realize just how tough they really are, and that they "can take quite a lickin' and still keep tickin'" ...

The higher temps seem to be normal for this engine and not as much of a stressor as I once thought.

You guys have made me much more comfortable with this engine; Now it's time to enjoy it.[smile].

C.



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4/9/14 2:24pm - Reply: 'Re: Manual Fan Control'
anthony.digirolamo
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If you wire the relay grounds to a switch or switches, if you have 2 fans,  the car will not set a code and they will switch off with the key.  I have had mine wired like this for a year and have never set a code.  I located my switches on the knee bolster. they are out of sight and reachable.  If you want to learn how to do this send me a message.  For l-98's.  Mine is a 90. 

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4/9/14 2:42pm - Reply: 'Re: Manual Fan Control'
cco
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1994 convertible, Polo Green 2 1G1YY32P9R5114269 ---------- 2006 Monterey Red Vert 1G1YY36U665125919----

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anthony.digirolamo said: If you wire the relay grounds to a switch or switches, if you have 2 fans,  the car will not set a code and they will switch off with the key.  I have had mine wired like this for a year and have never set a code.  I located my switches on the knee bolster. they are out of sight and reachable.  If you want to learn how to do this send me a message.  For l-98's.  Mine is a 90. 



Thanks Anthony -- the job is now done and seems to be ok -- tho it was explained that a code would be set but no CEL. So I'll see how it works out as it is.


Speaking of codes: I'm very interested in obtained a reader. I understand that my '94 is somewhat of a 'bastard' system being somewhere in between OBD1 and OBD2. My installer says there is a shop reader available but I need one that more affordable.

A reader for me would be more convenient that reading these codes thru the ALDL panel.

If anyone has any info on an available reader, I'd appreciate hearing about it.


BTW is my '94 a standard 12 pin connector such as this:

12-pin ALDL connector pinout:
F E D C B A
G H J K L M

Thanks,

 Colin.



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Colin
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7/8/14 7:47am - Reply: 'Re: Manual Fan Control'
cco
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1994 convertible, Polo Green 2 1G1YY32P9R5114269 ---------- 2006 Monterey Red Vert 1G1YY36U665125919----

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Adams' Apple said: Not sure how you're going to be able to wire up a manual switch in the circuit without it being "seen" by the PCM, and setting a code. Also, sometimes wiring up one like that can cause a backfeed into the circuit, and cause more problems.
Why do you need to control the fan(s) manually, anyway? You scared of that 235* coolant temp? LOL



Yes the PCM can 'see' the MFC but it does not throw a CEL. The PCM stores a 77 and 78 code but that's no biggie.


Love the manual control for when things appear to be getting too warm.


C.



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7/8/14 4:57pm - Reply: 'Re: Manual Fan Control'
davep85c4
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How about unplug the A/C high pressure switch located adjacent to the RF shock absorber? One grn/wht, one blk/wht wire. The fans will run whenever the engine is running, but still turn off at 45MPH.

Would be a good compromise for summer weather. Fans will run all the time, except in excess of 45 MPH when they're not needed, but set no codes, nor is any wiring cut or modified.  During the winter, or cooler weather, plug it back in. Fans will operate normally.

Sometimes the easiest solutions are the most elegant, because they cost nothing, are effective, do no permanent damage, and are simple to reverse.

This is all old news. The OP modified his car months ago.


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7/8/14 5:20pm - Reply: 'Re: Manual Fan Control'
davep85c4
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anthony.digirolamo said: If you wire the relay grounds to a switch or switches, if you have 2 fans,  the car will not set a code and they will switch off with the key. For l-98's.  Mine is a 90. 


Cooling fan control circuit  DTC's 77 and 78 do not exist prior to Model Year 1992. So no, your 90 will not set a code, because it "isn't in there".

DTC 77 and 78 set when the voltage on the control wire to the relay is opposite of what the ECM is commanding.
When the fan is off,  the control is High. When the ECM commands fan ON, the control goes Low.

Grounding the control like you did in a 92-up for manual ON will set a code if the ECM sees the control Low, but is not commanding a fan-on.

There are several ways to wire the fans so codes aren't set. The method I came up with is to connect a 200 Ohm 1w resistors connected to 12volts to trick the ECM when I've run the control to ground to command manual-On. The ECM will see the dummy load as a relay, and not detect the difference. It can still pull the control voltage low, if it commands the fan on, and the voltage goes high when it turns the control off.

Again, this is old news. The OP modified his car months ago. I would have done it differently than he did, but he's happy, so that's what matters.


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3/27/15 1:38pm - Reply: 'Re: Manual Fan Control'
Rhysing
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1991 Coupe 1978 Coupe 1965 Convertible

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davep85c4 said: How about unplug the A/C high pressure switch located adjacent to the RF shock absorber? One grn/wht, one blk/wht wire. The fans will run whenever the engine is running, but still turn off at 45MPH.

Would be a good compromise for summer weather. Fans will run all the time, except in excess of 45 MPH when they're not needed, but set no codes, nor is any wiring cut or modified.  During the winter, or cooler weather, plug it back in. Fans will operate normally.

Sometimes the easiest solutions are the most elegant, because they cost nothing, are effective, do no permanent damage, and are simple to reverse.

This is all old news. The OP modified his car months ago.


Sorry to bump an old thread, but I'm experiencing the problem. My fans work (if I turn on AC or Defroster) but with those off they turn on much later than I would like, I've just replaced waterpump, thermostat, and all new gaskets put in.

Next will be new radiator and lower cooling fan switch, but for a temp solution I was intrigued by unplugging the high pressure switch. Part of this could be my gauge is off (possibility) but it nears the 260 mark before the fans come on.

I have a 1991, and there are 2 plugs near the right shock absorber, one as described here with green/white wire but unplugging it did not start the fans. I tried the smaller plug next to it and still nothing. I then unplugged both and still nothing would get the fans running. Both of these plugs on are the small metal line that run into the air conditioning unit.

There is another larger plug up near the firewall, but unplugging that one did nothing also.

If someone knows how to make this work on a 91 I would really appreciate it.


|UPDATED|3/27/2015 11:38:18 AM (AZT)|/UPDATED|
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4/8/15 1:01pm - Reply: 'Re: Manual Fan Control'
wolfuser
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1987 C4 convertible 350ci auto white / red / white top appx 18k mls

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I fitted a manual fan override myself. switch is under the dash, poking through the dash carpet thing. thus, it is invisible until you really look for it (probably climbing into the footwell ;) as I didn t want to disturb the original plastic dash or center console.
I rigged it so it would ground the fan relay, doing the same thing as the ECU or temp sensor would do. the small additional fan, by the way, isnt very effective, so one would suggest to go for the main fan.
btw...it s a pain in the .... to run the lead from the engine bay into the cabin....

cheers
Wolfram
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4/8/15 7:48pm - Reply: 'Re: Manual Fan Control'
bblazer2002
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phoenix, AZ - USA

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1988 corvette completely stock

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One thing I did for my 1988 was purchased from corvette central a lower temp fan switch. I am in AZ and temp gets hot here in the summertime after changing the fan switch the temps run 210-220 and does climb to 240 in stop and go
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