Boost Lee

iTrader: (3)

THIS POST IS SPECIFICALLY AIMED AT THOSE STILL USING THE STOCK ECU.

I just learned something kind of critical today about fan switches in our cars after reading the wiring diagram for waaaay too long. What I learned is replacing the fan switch with one like the FC switch that is triggered at 95C instead of 105C only assists in cooling if any one of the other fan triggers has been turned on.

In other words, an upgraded fan switch does not turn the fans ON sooner. It only makes the fans spin faster if they're already on.

Look at the attached diagram. The fan switch relay is #3 on the far right. Notice that the switched side doesn't have a pole that comes from a 12V source. The switched side provides an additional ground to the fans. This means the fans would have to already have 12V going to them in order the completion of this circuit to get them turning when the fan switch is triggered.

But below 105C, the fans don't have 12v going to them from any of the the other 3 relays so they remain off. Each of the relays only provides a 12v source to the fans when triggered (A/C = Relay #1, coolant temp > = Relay #2 & #4

What this effectively means is there isn't anything that can be done to get the fans (with a stock ecu) to be triggered by temp to turn on sooner than 105C.

Yes, A/C can be turned on but then the fans efforts are being directed @ coolant AND the a/c condenser.

I think what could be done is de-pin wire at the ECU that provides ground to trigger fan relays #2 and #4 and run it up to the wire from the fan switch. This should start the fans at 95C @ middle speed. I guess I have a project for tomorrow night.


If I'm mistaken on my interpretation of the manual, please correct me and let know where I screwed up.

Mps_hell

Don't think I have seen that diagram before...... It's a good one lol. For a 2 speed fan, maybe try the fsm one

It loops back on its self and would blow if it would even run

DaleClark

iTrader: (55)

Very interesting! I think you may be on to something there.

I still think the FC thermoswitch is a good idea regardless. I can't remember what the temp is the stock ECU kicks the fans on, though.

Dale

Boost Lee

iTrader: (3)

Now that I've had some sleep, a couple more things.

In order to test this (at your own risk), run out to your car and disconnect the 4 relays. Don't worry they're all the same. The A/C connector is different, but I'm going to omit it for this test because I'm too lazy to explain how to test it AND the other 3 separately. With the KEY ON, Test the voltage across the larger wires in each of the remaining 3 connectors. You'll find that one of them doesn't have 12V (NOTE THIS CONNECTOR, IT IS THE FAN SWITCH CONNECTOR).

At any point during this test, you can turn on your A/C and get another fan input for additional speed.

Now create a jumper and jump the two larger wires on any one of those connectors (at your own risk). This simulates the relay being triggered and turns on your fan. Now that any one (or both depending on which connector you choose) of your fans is on, check the voltage across that terminal that didn't have 12V (fan switch). It should now have 12V, but that isn't high amperage 12V. It is the residual left over after your fan or fans have "taken their drink" from the 60AMP lead feeding them. Jumping the large wires on that connector will lead to a speed increase, because you're providing a path for that 12V with whatever current is left in it to go to ground. If you then jump the 3rd terminal, this will give you a larger speed increase than what the fan switch provided because it provides a 12v from a circuit before anything else has had a chance to "drink from it".


I also realized that even PowerFC users can't use that trigger to turn on their fans. The fan control the PowerFC provides is for relay #2 and #4 which are individual triggers for each fan. If those are triggered @ 85deg and the FC thermo is installed, the end result will be:

Low speed fans from 85C
---> med speed fans at 95C


I think the only way to trigger the fans sooner without having programatic control from an ecu or having to use A/C is to simulate the electrical load input at the temperature that you want. The alternative would be modification to the temperature sensor signal, but that would result in timing and fuel changes.


More to come if i figure out another trigger.

Boost Lee

iTrader: (3)

Based on temperature, the fans come on at 105C
The fan switch triggers at 108C but that only helps because the fans are already on.

00SPEC

iTrader: (9)

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Mps_hell

Makes me feel better about ripping all the cooling relays out last year and going after market

jmadams74

Your post highlights the importance of being able to set the "fan on" temperature with the PFC. Once the fans are on, then the lower temperature control switch (as well as a/c or other electrical load) can kick them up to higher speeds at lower temps.

wstrohm

IMHO this subject was pretty well covered in DaleClark's thread... but read all the posts for a complete understanding of the effect on overall cooling and the effect of Mazda's "cooling fan mod."

Sgtblue

iTrader: (16)

IMO, there are only a few good reasons for doing that. Very few that I can think of. My bet is that your consonance is premature.

Boost Lee

iTrader: (3)

What specifically about Dale's thread are you referring to?

Julian

iTrader: (14)

Been years and years ago since I traced the relay functions, but what I remember is that the cars had a recall where Mazda changed the wiring setup, don't think the manuals portray as-modded. Only recourse is to test circuit logic.

Boost Lee

iTrader: (3)

Actually in the 4th post, I describe testing the actual logic of the circuit and it matches the diagram that was included in the first post. What would be "fan"tastic is if another member would, in the interest of proving or disproving a statement, take a few minutes and go through the exercise of independently testing the proposed theory.

See the pun I made there? Yea, I'm pretty funny!

00SPEC

iTrader: (9)

I am 90% sure that I can hear the fans come on BEFORE 220F. unless my temp gauge is off by 20 degrees.. unfortunately my baby's at my mom's house until I finish this clutch job, but definitely will test this.

EDIT: running FC thermoswitch

2slo4my7

iTrader: (3)

Just went out for a drive and my fans were turning on at 205-208F just before 210F with fc thermoswitch. Fans used to turn on at 220F before so not sure what your looking at but I think you could be wrong. Didn't have anything else on either like AC.

Boost Lee

iTrader: (3)

Thanks a bunch you guys. Just to confirm, where is your temp sensor located AND you're running with the stock ECU?

2slo4my7

iTrader: (3)

I have the Pettit ECU which I don't think is any different for fan temps? Correct me if that's wrong.

Can't remember exactly which line the temp sensor is on but its located along the firewall behind intake/throttle body. Always been pretty accurate since, as I said, I used to see the fans kick on at 220F before FC thermoswitch.

Someone also once told me that fans would kick on a couple degrees sooner if you turn the dash lights on.(not turning lights on completely but just one click on the light switch)

Is there any truth to this?

Boost Lee

iTrader: (3)

I'm asking where your temp sensor is at because I think we should be measuring at the same point. Measuring at different points can yield different readings. My sensor is in the upper radiator hose.

Yes turning on the parking lights activates the electrical load circuit which turns on the fans, but I don't remember where in the FSM it says how much sooner

2slo4my7

iTrader: (3)

It is possible that we would have different readings. I hope my temp gauge isn't off by 10-15F though!

Was reading this thread again. Seems as though racerx7 is saying the same as you.
Fan thread

According to Dale's first post, turning on your parking lights would also only increase the fan speed and not make them turn on at a lower temp.

So if you are both correct, can we simply not send power/ground from the thermoswitch to the proper relay in order to make the fans turn on at 95C? fooling it into thinking it is getting a reading from the ECU

Seems odd since I'm pretty sure I remember a difference in temp when I did the thermoswitch mod. I could be wrong since it was 4-5 years ago.

KevinK2

I see what you are saying, OP, but as usual, Mazda is correct. Based on the FD wiring manual (Z42 B-2), as well as the summary you copied, there are 3 connections to each motor to control speed (motors run in parallel, as a single fan motor ). The catch is one of the connections is a gnd, and the 2 others are 12V inputs. That leaves the 4th connection as a permanent gnd. Also, three of the relays have 12V supplies, vs relay 1 for the AC input ... it has an ignition hot for the relay's coil.

SOoooo, when the fan switch is closed / grounded, it provides a gnd to the motors by way of relay-3, resulting in med speed. The voltage for the motors comes from relays 2 & 4, with a gnd from the fan control module or the ecu.

I have the "fan switch mod", where I have an extra switch that grounds the test lead of the fan-control-module, which is like closing the FC switch to gnd. I just went out and turned the ign on (AC off), and engaged the switch and the fans came on at medium speed, per the Mazda manual test proceedure. If you run them for more than 150 sec, and turn off the switch, the speed drops to low. This is all done by the fan control module, that was added in 1993 models so fans could stay on after the ign was off.


This is my post from a 2005 thread about the FC switch:

https://www.rx7club.com/3rd-gen-arch...6/#post4607146

------------------------------------------------------------------------------

"However, I am perplexed as to why I have a 115 degree switch? Maybe because of the automatic tranny?"

Me -> This is a separate trans switch for autos, located where one of the plugs normally resides in the fill neck hsg. If coolant hits 240F, atx logic engages torque converter lock-up more often, to reduce heat from torque converter.

You still have 108C fan switch, behind t-stat. Replacing with FC-or-miata switch means, with ac off, fans come on 1st at 207F at med speed, vs 221F (ecu controlled) at slow speed then 226F at med speed. Note this may only change med speed trip to 221F for some.

Alternative is to run with parking lights on, or cabin fan at 3 or more, in hot traffic. This trips fans on slow at about 200-210F.

--------------------------------------------------------------------------------------

The previous link, by Dale Clark, describes correctly the sequence of operation.

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KevinK2

Correction, the fan switch grounds the coil for relay 3, which then provides grounds for the fan motor relays 2 and 4. With a stock fan thermo switch, it provides the lowest temperature (221F) where the fans come on low speed. The FC switch lowers that initial fan operation temperature. Then when the temp rises to 226F, the ecu uses another thermo-sensor to set the fan speed at medium. Not if the AC is ON, those speeds will be "up 1", so cold coolant results in low speed, fan switch triggers med speed, and the high temp 226F to ecu gets fast speed.


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Boost Lee

iTrader: (3)

This entire explain is with A/C turned off!!!


For the fans to get activated by temp, the thermosensor (only 1 on the car) not thermoswitch (also only 1 on the car) has to report 221F like you said.

I'm sorry, but the way I read that diagram is that the fan switch (thermo switch) provides a ground for the coil on relay 3 (you and i agree here). This then provides an additional ground for both FANS, not the fan relays. Look again at the diagram in the first post. The right side of relay 3 only serves to connect the bottom right leg of each fan to ground (no connection to a relay).

So if you consider the fans in an off state at 220F. At 221F the ECU simultaneously triggers relay #2 (which provides 12V to fan 1)and #4 (which provides 12V to fan 2) based on input from the thermosensor. That is speed input 1. At 226F the stock thermoswitch activates providing ground for the coil in relay 3 which then provides a ground to both fans (not their relays). This is speed input 2.

Now, if you consider the fans in an off state at 94 deg C (201F) and the FC thermoswitch activates at 95 deg C (203F), providing a ground to the coil on relay 3 which then provides a ground to each fan. Realize that at that moment each fan has 0V coming in on each of its two inputs (top left and top right of each fan in the diagram) because the relays #2 and #4 won't get triggered until the thermosensor reports 221F to the ECU. Remember, relay #3 only provides a ground, not a 12V source to the fans. So the fans will stay off. But when they do get activated by the ECU when the thermosensor finally reports 221, the fans will engage at speed 2.

I didn't make any claims about Mazda being wrong. I just stated that we've (the FD community) been reading the FSM incorrectly and assuming that putting in an FC thermoswitch makes fans come on sooner. It most certainly does not.

KevinK2

No, the last sentence of what you quoted is about AC-on. My bad typing put down "Not" instead of the "Now" to start off that last sentence. It about ac on, and makes more sense that way.


I had stated it correctly, ground to motors, before I made the correction you quoted. I also had it correct in the link I provided. That correction by me was just brain fade.

I'm not sure where you find that ecu logic that does not allow the motor relays to be actuated by grounds. The ecu sends voltage to the motors by providing a gnd to fan relays 2 & 4, and that is for all operating modes. The thermoswitch for medium speed at T2 closes to allow an extra ground to the motor.

What I have written, and tested, is that by adding the FC temp switch, you LOOSE the slow speed function, and what was the control for the higher temp (fan switch) is now the control for the lower temp. I just tested with my cabin fan switch, in parallel with the water thermo switch. With eng cold, ign on, I turn on switch and fans come on at med speed. Turn on AC too and I got high speed.

So I disagree with you, in that the fans will come on at a lower temp with the FC switch. You just loose low speed.


I have read the FSM correctly, imho, unless you do some testing to prove me wrong. You can make the fans come on sooner. I think your mistake is thinking the motors are voltage controlled for the fan switch speed, vs ground controlled, which is what the fan switch controls.


In the FSM, there is a test for the oem thermo switch. At 214F, .5 ohm max (closes). At 226F, 1 Meg ohm min (open ! ). Something to think about ... don't need relay 3 for fan control if temps above 226F.


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Boost Lee

iTrader: (3)

Kevin, when you post a correction, I take that as meaning that the reader is supposed to ignore your previous statement, right? Well, I did that and addressed the statement that you said was the "correct one". Now you're correcting the correction... there's a bit of clutter here man!!!

Ok, with that said, let's move on.

My first statement in my previous post

"This entire explain is with A/C turned off!!!"

was to indicate that I was describing the behavior of the car with the A/C off. I wasn't commenting on your previous post.

I never made claims that the motors were not activated by grounds. I actually stated multiple times quite clearly that the relays were activated by grounds (in agreement with you).


I'm not sure what you're referring to in this statement.


Instead of debating how the rest of the fan system works, focus on the heart of the matter which is:

With all other fan inputs turned off, do the fans turn on at lower speed or when the FC Thermoswitch provides a ground to relay #3 at 201F instead of 226F (stock thermoswitch activation temp)?

I say no, you say yes.

If you agree the above statement is the issue, please walk us through the wiring diagram for what happens when the thermoswitch is triggered.

KevinK2

Again I apologize for my disruptive "correction to a correction". No excuse,
guilty as charged.

We agree on most of this, but the key to the discussion is as you just said in bold.

But before that, you had questions about my last post, with two quotes in your last post:



1st quote, This was about your prior statement that when an FC switch is about to turn on a fan, you said "Realize that at that moment each fan has 0V coming in on each of its two inputs" .

I questioned how you knew there was zeo volts at the 2 motor inputs. Yes, one input is for AC-on only, but the other one will see voltage if the ecu provides the relay's ground. There is nothing in the FSM-wiring that suggests the ecu will not provide the relay ground in this case.

As I said before, I have a new switch parallel to the fan-switch. With engine COLD and off, ign on, I could turn the fans on medium speed with that switch on. And when I turned the AC on too, fans went to fast speed.

That test supports what I have been saying ... there is voltage at the non-ac motor input most/all the time ign is on.



2nd Quote, With more explanation: (AC off) The OEM thermo-switch for the call for medium fan speed at the 2nd tempeature point (226F), closes at that temp to allow the variable ground at the motor to close. The other motor ground is permanent.

I hope that clears it up for you.




Now for your question in "bold" text:

"With all other fan inputs turned off, do the fans turn on at lower speed or
when the FC Thermoswitch provides a ground to relay #3 at 201F instead
of 226F (stock thermoswitch activation temp)?"

As I said before, with the FC switch, the fans come on at med speed at about 202F, and apparently override the normal ecu low speed on at 221F. And I never said yes to that question in any form.

But from your 1st post:

This is wrong, the FC switch does make the fans come on sooner, and it also eliminates the low speed fan mode .... I becomes a 2 speed fan.


I bought the FC switch, but did not install it. I felt that it would turn on the fans just as the t-stat was wide open, and needlessly cool the radiator contents to about 185F before it turned off, wasting the fan motor run time. If there were a 215F switch, I'd go with it. For now, I use my extra switch to turn on the fans when I know coolant is heating up toward 221F. I even put a resister in parrallel with the temp-sensor for the gauge, so it shoots up when the temp exceeds 226F. Handy at track events.


I just tested the FC switch, and it closed at 202F, and opened again at about 185F.

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