Boost Lee

iTrader: (3)

Hey wstrohm! Can you clarify if the FAN Mod you're referring to is an actual modification or if it's the Fan Recall implemented by mazda? If it's not the Fan Recall, please detail what needs to be done to implement the Fan Mod (just hoping to have it in one post rather than generate a bunch of searching for people)

adam c

iTrader: (2)

fan mod

Cooling Fan Modification

wstrohm

Page E-17 of the 1994 Workshop Manual gives a table of switch state vs. temperature for the OEM FD fan switch, which Mazda calls the "Water Thermosensor" on this page. At 101°C (214°F) it says the resistance of the switch should be 0.5 ohms max, and at 108°C (236°F) the resistance should be 1 megohm minimum. Unfortunately that indicates that the switch works opposite to how it really works, i.e. it actually closes at high temp. Assuming the error in the manual is just a reversal of the operation but the temperature range is correct, the average of 214°F and 236°F is 225°F.

I was writing of the Fan Recall; sorry if that wasn't clear.

(P.S. Still working my scanner problem, sorry.)

KevinK2

The 94 OEM schematic, w/o FCM, is shown on Post#1. It is the same as my 93 version. Both come from the Factory Wiring Diagram Manual.

There is also wiring info for the "cooling fan control" in section F of the Service Highlights, as you know. The 94 version is on Post#5, but it DOES NOT show the Engine Load Unit. My 93 version DOES NOT show the FCM. The complete diagram and table are in Post#56 and should look familiar ... you posted the same thing in 2005. It includes the ECM, FCM, and the Engine Load Unit.

The complete diagram and table are informative. Looking at just the "fan switch" it is clear that it is "on" when the coolant is above 226F. With AC off, relays 2, 3, & 4 are on, providing voltage and a gnd for the B-D side of the motor, and no voltage to the A-C side. This would be the "middle speed", per the circuit and the table.

With temps below 212F, no loads, and AC on, only fan relay#1 is "on", and the speed is low.

Soooo, with AC off, the coolant switch is for middle speed at 226F+ temps.
The A-C side of the motor is slow speed, and the B-D side is middle speed.

Correct?

I believe only the earlier 93's with the FCM added by the dealer, will have "instant on" fans with the "fan Mod" switch. Others will have about a 2 minute delay. See Notes on Post#57.

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KevinK2

If the Notes from my post about the FCM test sequence are correct, and the Pxxx numbers are part numbers, you could get the early version, with instant fan on like in my 93FD. This would allow a working "Fan Mod" switch to be installed.

Notes:

A) pre Apr 1 93, P0210660, fan operates by ign on

B) after Apr 1 93, P0210661, fan operates 100-150 sec after ign on

C) wait for 150 sec after ign on for both groups

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KevinK2

I looked at my spare waterpump, and think I know why you don't see the 185F stop point for the FC switch. Your gauge reads temp of coolant in the engine water jacket. The switch is located in the pump housing, where the cold end of the rad returns coolant, so 185F for the cooled water is reasonable, and you would have to put a sensor in the return line to verify this.

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wstrohm

The text with the lower red arrow in the diagram of Post #1 is misleading. The indicated circuit location will have +12 volts on it only if the fan relay contacts are open, which is only if the Fan Switch is open. In that case, if and only if there is +12 volts on the "B" terminal(s) of the fan motors, one would see +12 volts on the "floating" D terminal(s), fed through the fan coil winding(s). In this case the fan would NOT be running, unless at low speed, since no current would be flowing in the medium speed circuit.

KevinK2

In short, the red marking on that circuit labeled 12V is wrong. If a relay coil is not grounded by the grounding wire, that wire will be at 12V, if there is voltage supplied to the hot side.

In shorter short, a coil wire is a conductor.

I was hoping you would respond to my post #79.

So you also have the sequential turbos?

KevinK2

wstrohm, some questions on your set-up. You have the FC switch. Based on coolant temperature alone, do your fans come on at a lower temp, vs with the FD coolant temp switch? If so, what fan speed are they at?

And with your extra switch to gnd the FCM test wire (coolant fan mod), do the fans come on right away, or after about a 2 minute delay?

Thanks

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KevinK2

The FC fan switch ("Engine Coolant Temperature Switch" in the schematic above) closes Fan Relay #3's coil at 207°F instead of 221°F like the FD switch. Fan Relay #3 responds by connecting the "cold sides" (Terminals D) of the fan motors to ground. This is an "enabling" circuit for the medium-speed fan coils "B-D."

Medium speed cannot run unless Terminal D is grounded. But in order to run at medium speed, Terminal B, the power supply to the fan motor's medium speed winding must also be at +12 volts.[/quote]

I agree completely. For the following, I reversed the cases.

OEM Fan Control (No FCM )

Without the Fan Mod, the Fan Control Module does not exist. The fans cannot run after ignition is turned off. The schematic for that case (from the 1994 FD Workshop Manual, page B-2) is found on post #1, ignore the red markings. (Info there also required looking at page B1-b to determine ECM terminal 3D was the control for power to the fans.) EDITED by KJK to provide the post#1 reference.

You are suggesting that the fan motor's medium speed gnd "enables the circuit for when the ecm decides to supply voltage to the motor's medium speed hot input. I believe it's the other way around. The fan switch has a specific temperature when it closes, FC of FD, and the voltage supplied by the ecu enables the fan motor to run when the temp switch closes.

Here I think you just breezed by how the low speed is actuated. It's ON care of relay#3, when the ac cabin switch is on, grounding this relay's coil (to keep the condenser from freezing). But for when you need it on for the lower temperature, 221F, that same AC wire must have another ground from the ECU, based on thermosensor input.



That is likely true, but, that assumes the FCM takes over normal operation, before the engine is shut off. I can also see the ECM functioning like it did with no FCM, but using the FCM to control fan resonse after the engine is turned off.

The logic must be that, with AC off, FD fan switch in use, low speed comes on first at 221F-226F, based on the ECM and it's thermo-sensor. But then if temps rise high enough to trip the 226F+ fan switch, the low speed looses the voltage to the motors, but allows it for the 226F medium speed. ( if both sides of the motor are powered, that would create HIGH speed which is not possible, unless the AC is on. ) I learned early that no matter how hot the coolant gets, you will not see high speed at the fans, unless the ac is on.

OP's question: Does adding the FC switch cause the fans to come on at a 207F, vs slow at 224F, and medium at 226+F with the OEM switch? I think with limited info on the fan's slow speed operation, it is better to rely on owner's (with linear gauges) measurements of coolant temperature when the FC switch is installed.

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2slo4my7

iTrader: (3)

That would make sense a lot of sense!! Also probably why I'm seeing the fans turn on around 207F instead of 202F.

Thanks!

wstrohm

Since I have the stock temp gauge, which is highly non-linear around the normal operating temperature, I cannot see any difference in its operation between FC and FD fan switch in daily driving. The fan speed with A/C on is indeed normal low-speed (A-C with A/C!) and no B-D. When the fans come on without A/C on, they always run at medium speed.

I do not have an "extra" switch; once again, I was referring only to the Mazda Fan Recall, and I apologize if my usage of "fan mod" was confusing. My '94 fan operation was originally OEM (bought new), then had the Fan Recall added, after which we experienced run-down battery problems due to the fans running after shutdown. I then removed the "fan mod" (all Fan Recall circuitry) and replaced the FD switch with an FC, after which battery problems ceased.

I agree with your edit adding reference to Post #1, for me to add the OEM schematic here would be redundant.

As to your Post #79, I agree with everything you wrote. And, your interpretation of "enabling" is just as valid as mine... whenever two independent signals are required to activate a function, I tend to call them in chronological order: the 1st "enables" the circuit and the 2nd "activates" it. Just a personal thing.

KevinK2

Do you have a separate linear coolant temp gauge?
Could you tell if the fans came on at a lower temperature ( ~207F vs ~221F) with the FC switch?
What speed do they come on at, slow or medium?

I heard that deleting the FCM eliminates a lot of wireing harness length under the hood.

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KevinK2

>Could you tell if the fans came on at a lower temperature ( ~207F vs ~221F) with the FC switch?
>What speed do they come on at, slow or medium?

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KevinK2

In the quote above, you had already answered my later, repeated question in the quote below:

Sorry wstrohm, my bad.

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Mazderati

iTrader: (3)

Sounds like there are two takeaways so far.

1. In cars [/i]without[/i] the fan recall, using the FC thermocouple turns the fans on at the same stock temperature (221F) albeit at a higher speed (medium instead of low).
2. In cars with the fan recall, using the FC thermocouple turns the fans on at a lower temperature (207F instead of 221F) and at a higher speed (medium instead of low).

Seems like the fan recall, while not great because of the drain it puts on the battery after shutdown, is beneficial when used in combination with the FC thermocouple.

wstrohm

Not exactly. the 221°F temperature (actually 214°F - 236°F per the manual) is not relevant when the FD fan switch is replaced by the FC switch. All discussion about fan operation with the FC switch revolves around 207°F, because that is then the cooling system's medium-speed threshold. Yes, the fans will run at medium speed above 207°F (or so). Low speed by itself is operated by the A/C switch controlling the Cooling Fan Relay #1, as seen in the Post #1 schematic.

Mazderati

iTrader: (3)

If the factory fan-speed-to-coolant-temperature thresholds don't change with the addition of an FC switch, then we're back to the question of whether or not the FC switch helps in cars without the fan recall. Is that fair to say?

KevinK2

Correct on Q2, but the temp change is from 226F to 207F, not 221F. The 221F set point is programed in the ecm, which reads the temp fron it's thermosensor. Another set point programmed in the ecm include about 205F for specific Engine Loads (EL's).

Regarding Q1, the FC thermo-switch (not thermocouple) changes the first turn on point, based on the 207F FC thermo-switch, at 207F at med speed.

KevinK2

In my 93 FSM, the test gives a 214F closed (on) and 226F open (off) ... 236F?

I'll retest my FC switch, for high temp open. This spread is logical, as you don't want the A-C slow side of the motors on (via relay grounds from ecm 3D, or FCM E), when the fan-switch turns on the medium speed, which will result in HIGH speed as the first fan on speed based on temerature rise.

KevinK2

For me, LOW speed operation logic of the fans is not clear. Most/all diagrams show that relay#1 (also used for AC) must be "on" to supply voltage to the motor's A-B windings. The ground is fixed on that side of the motor.

But, the tables have a data-row for when the temp is between 221F and 226F. This would be the first temperature point for the fans to come on at slow speed (AC off). But, when you look at that row, with AC off, it shows the temerature switch is also off, it shows the "controlling" relays #1 and #3 are both off, yet the fan relays #2 & #4 are both on, with the fan speed at LOW.

That seems imposible with relay#1 off, that supplies low speed motor voltage. I can see it supplying MED speed to the fans, using the FCM and the ECM, and even the MED speed FD coolant switch.

Any help with this logic would be appreciated.

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KevinK2

....and, for the next step to MED speed at 226F+, based on the Coolant fan switch, the slow speed side of the motor must be "turned off" to avoid high speed. That would best be done in the ECM, where coil grounds for slow speed relay#1 could be opened at ECM 1E, when the fan relays #2 & #4 are energized by the coolant fan switch, by a ground at ECM 3D.

Then if AC switch is engaged, there is a different path for a ground for the slow speed, and with both slow and med speeds engaged, you get High speed.