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Old 06-02-2007, 07:44 PM   #1
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Default Problem with cooling fan mod

I was attempting a dual stage fan mod with a SPST relay and the thermosensor:

relay pin use
Pin 30 to A/C side fan black/blue stripe
Pin 85 to thermosensor
Pin 86 to driver side fan yellow
Pin 87 to driver side fan yellow

This resulted in the driver's side fan not coming on, so I disconnected my relay and still nothing. There was no voltage at the fan. The 30A fuse under the hood is good. The under hood cooling fan relay has 14V at the supply and coil pins. The coil ground pin has ground. If I jump 87 to 30, the driver's side fan comes on. This leads me to believe that my fan relay went bad.

Now the question is why it went bad, and what can I do to correct the problem.
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Old 06-02-2007, 08:49 PM   #2
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Exclamation Dual fan mod warning

Returned wiring to stock. Replaced relay. All is good.

Jumped the driver's side fan +12V to the pass side fan +12V. The fans turned on at a slow speed, then the fuse smoked.

Dual fan mod + MSPNP = BAD

<EDIT> Problem found. The +12V lead on the a/c fan goes to ground when the a/c is off.

Last edited by Ben; 06-03-2007 at 03:56 PM.
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Old 06-02-2007, 09:14 PM   #3
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Can you do something like this?

I did this on my 99 and it works perfectly.

http://www.fastforwardsuperchargers....6&postcount=32
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Old 06-02-2007, 09:23 PM   #4
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Something is possible. What, I don't know. The MSPNP runs the fans differently than stock.
I'll get with Jerry about it. Maybe he can come up with something similar to how the Hydra runs the fans (which is IMO the best way).

ALSO, apparently the fan fuse is also the wiper fuse.

At least I got to adjust my clutch pedal out today. Lack of working cooling fan ruined the rest of my miata plans.
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Old 06-03-2007, 12:19 AM   #5
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do they not both pull to gnd on the ECU / sensor side?
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Old 06-03-2007, 12:41 AM   #6
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Well it looks to me that the driver's side fan works by the MS supplying +12V on the coil of the fan relay. Looks like the coil always has ground. Interestingly, it also always has +12V at 87 regardless of key position. So a timer circuit to keep the fan on after ignition off may be in order too.

I'll get with Jerry after the weekend and figure something out. Perhaps a new pair of SPST relays with the power source from battery. There might be something better. I'll think on it.

Also, I was kind of shocked at the slow speed both fans ran at when I did the traditional dual fan mod off an oem relay. It's been stated that it isn't up to 2 fans, and I'm agreeing.
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Old 06-03-2007, 01:15 AM   #7
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All the more reason to hardwire that **** and run thermoswitches of toggles, if you are a serius enthusiast. But a higher rated relay should do the trick as well you might pull a thicker power wire for the primary feed when 2 on past 200 F so you dont lose fan speed do to a overlaoded wire. Or worse get some smokin results. Could you just have a switched bypass on the AC circiut for 200+ F running. You know just jump over the AC relay with your own. this way if it is switched to 200+ it comes on if the AC is on it comes on this might not be a bad idea my WI is wired kinda like that so i can do diagnostic with my boost gauge.
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Old 06-03-2007, 02:25 AM   #8
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so wiring the AC fan in parallel to the normal fan so that when one kicks on both turn on doesn't work with the MSPNP? the hanook way or whatever that dudes site is called.
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Old 06-03-2007, 03:14 AM   #9
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Well I woke up from a sound sleep and thought of the solution. Theory is semi tested, will get back to it tomorrow.

When the a/c fan is off, the +12V wire goes to ground. I just tested that. Explains why the fuse smoked.

I used a SPST relay. I'll try again with a SPDT, and I'll also bring power in from the batt or something....
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Old 06-03-2007, 01:46 PM   #10
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This basically can't have anything to do with the MSPNP--- it's just activating the relay. If the circuit that it's activating can handle the extra current you're telling it to pull (by adding the second fan) when the stock ECU activates that relay, then it will when the MSPNP activates that relay.

I think you're on to something with the AC + wire going to ground when it's not activated-- I think I recall that being mentioned in the writeup as well. Yep-- just looked it up-- apparently the AC Relay, when not active, grounds it's 12v+ wire. So you'd want to cut it's connection to the fan and not let AC activate the fan any more.
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Old 06-03-2007, 01:53 PM   #11
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As far as how the Hydra runs the fans-- how is that exactly? Two programmable temperature points? Is this feature completely plug-n-play? Anyone have first-hand experience with it on a 90-93 car? Seems to me it couldn't be completely PnP.... there is only one relay on the 90-93 cars that controls both the AC clutch and fan. Activate the fan by the relay and the AC compressor is coming on too. Unless you do some rewiring that is.

The 94-95 is different-- there are two relays, one for the fan, one for the compressor. We could theoretically allow dual staged fan control there at the expense of one of the few remaining outputs that we had left for DIYers to use for what they may want to. Though I'm not sure that's a good idea... It would reduce DIY expandability by taking away available I/O that some would consider more valuable used for something else... thoughts?
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Old 06-03-2007, 03:32 PM   #12
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Jerry, I have a great working solution.

The big problem with my initial idea was that the a/c fan +12v goes to ground when the a/c is off.
Here is what I did to make it work, and why I think it's the best way to go about it.

I used a SPDT relay instead of the SPST. This allowed me to connect the car side of the a/c wire into a NC terminal. I sourced full time +12V from an unused fuse position in the underhood fuse box. I crimped a spade connector onto a 14ga wire, and was able to plug it into the bottom side of the fuse box in the formerly unused position. Ground signal comes from the thermosensor on top of the thermostat.

So:
85 to thermoswitch
86 to +12V
87 to +12V
87a to car side of fan wire
30 to fan side of fan wire

Result:
Driver's side fan operates by MSPNP at set temperature.
Passenger side fan operates at 206F (thermosensor close temperature) or with A/C activation. This creates 3 seperate, independant fan circuits, each individually fused. If the driver's side fan fuse or relay fails, the passenger side fan will still work. If the A/C relay fails, the passenger side fan will still work at engine temps over 206F. This does not waste any outputs on the MSPNP.

I used full time +12V on the relay coil so that the passenger side fan could operate key off, if the motor is over the 206F threshold. This seems to work well, but I will monitor the duration of the on time to see if a timer circuit is warranted. So far, if the passenger fan was on at the time of engine shut down, it stops running within a minute or two.
If one did not want the fan to be able to run with the key off, they could use any switched +12V source on pin 86.

2 pics attached. The red arrow in the first shows where I put the SPDT relay. The arrow in the second shows the unused fuse holder I was able to use. I used a 30A fuse (fusible link). The fuse to the right is the fuse for the driver's side fan and is 30A.
Attached Thumbnails
Problem with cooling fan mod-fanmod1.jpg   Problem with cooling fan mod-fanmod2.jpg  
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Old 06-03-2007, 04:42 PM   #13
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That does sound like a pretty slick solution Ben... good work man. I like the fan staying on for a couple minutes after shutdown using the thermo switch-- as long as it's just a couple minutes and your battery can take it that's pretty 'cool'...
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Old 06-03-2007, 07:58 PM   #14
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yeah the hydra has enough outputs to spare so the two fans get separate temp points. then the A/C is dioded in to the circuit for the 2nd fan at the ECU harness.
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Old 06-04-2007, 07:20 PM   #15
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rewire them, have ms control a relay

and be done with it
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Old 06-04-2007, 10:01 PM   #16
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those unused slots in the fuse box are a great place to pick up power, that is where my DRL's are powered from.

I know some honda fans run for a few minutes after shutting the car off if the temps are high. It doesn't seem to be a problem for them.
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Old 06-04-2007, 10:42 PM   #17
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I've gone for 3 "mild" drives with the driver's side fan de-powered to stress test the a/c fan mod. It works.
When I turn the car off, it continues to run for 2-5 minutes. I didn't check current draw myself, but those who have claim the a/c fan pulls 6-7 amps.

So even 10 minutes (that's double my longest observed) of fan run time is no more than 1.2 amphours. I don't know what the battery is rated at, but it's probably 30-36 amp hours. So it's NBD.

Obviously leaving the fan on with the engine off isn't going to circulate coolant. But it's amazing to feel hot air being pushed out of the space between the fenders and hood, and also between the headlamp lids and the hood. When the fan shuts off, the passenger side of the hood in front of the power bulge is cool to the touch. The driver's side is still hot. I can only conclude this is a good thing.

So I don't have any REAL data on effectiveness, but it passes my super scientific "touch it and see if it's still hot" test.
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Old 06-04-2007, 10:44 PM   #18
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that's how i know my NACA suct works better then my old TSI

sounds like a cool idea, my parrell wiring seems over the top with my radiator...I've yet to see 182° CLT with my cooling mods, with 100° intake temps at cruise.
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Old 06-04-2007, 10:50 PM   #19
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I'm yet to see 100F intake temps at cruise

You wanna up headlamp lid for me?

But since adding a radiator cover plate and removing the front turn signals, temps have gone down 4-6F. Peak temps under boost are the same, but they recover much more quickly.

Oh, one of the dudes from m.net wants to de energize the cooling fan relay at speeds over 45 by tapping the VSS circuit. So I'll design a circuit to do that (eventually).
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Old 06-04-2007, 11:29 PM   #20
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If my dremel didn't burn up when I did Tom's I do it.
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