Disable electric fan at speed?

[Allan]

Although my aftermarket temp switch works well with my electric fan, I'd like to find a way to automatically disable it over 40 mph. My coolant runs cooler with the fan off at highway speeds.

The MN12's that come stock with electric fans have EEC drivers that control fan operation. Our 5.0 cars don't have any electric fan or its controls. I've thought about doing MadMartigan's Mustang ECU swap because it can control high and low fan speeds. Just not sure what else would be needed to make the fan part work (adding wires or rewiring the EEC fan outputs or adding an ICRM, etc.).

Any ideas besides EEC swaps?

-Allan

[RalphP]

Easier, use a stand alone controller.

One that pops up with Google is http://www.streetrodstuff.com/Products/1042/

Disclaimer: I don't use one, I've got the old fashioned "HP? We gots lots of HP!" metal fan on Sweetie's 5.0

RwP

[Allan]

None of these will cutoff the fan power when running at vehicle speeds.

A running fan is an air flow restriction over 40-45 mph. If your front air dam is functional, you'll get more air across your radiator than the fan is able to pull. At least that's the case with my fan (from a 95 LX) and my stock radiator. My temps rise on the highway. If I pull the fan fuse, I run normal temps on the highway, so long as I stay above 40.

Disclaimer: I don't use one, I've got the old fashioned "HP? We gots lots of HP!" metal fan on Sweetie's 5.0

I ran the stock fan for years until my fan clutch went bad.

[RalphP]

Use one of the ones that have the radiator probe.

That way, if it's cool enough, no fan.

Being stand alone, it would be driven by the temperature of the coolant ONLY, not by any other inputs to the EEC, so by using the adjustable one, you should be able to get the best of both worlds.

I'd STILL have the A/C override, so that you'd get fan action while the A/C is on, no matter what - but that's because I live in Louisiana, where 100F days are not unheard of.

Past that - maybe add a relay to the fans, so that you can disable them at your desire? Use the NC contacts, and wire the coil to a switch on the dash, with a big "NO FAN" light.

RwP

[bowez]

Tapping the VSS is the best way to do it if know the signal.

Other options include a simple switch or tapping the Speedo directly (at 4.0 will be doing ~40mph).

[91 XR7]

I think Painless now has a setup you are looking for..

It's a Variable Speed Fan controller that also has an input from the speed sensor that will disable the fan when the car is at a certain speed (Programmable) along with Manual override (3 position switch? Fan on all the time, Automatic, Fan off all the time??)

Click here to see it

Only system at this time that I know of that has a VSS input

[bowez]

If you have cruise I may have come up with a work around. Though need to do some testing.

Will shut the fan off at 30mph though.

[Allan]

Use one of the ones that have the radiator probe.

I'd STILL have the A/C override, so that you'd get fan action while the A/C is on, no matter what

Ralph,
The switch I installed has the probe mounted in the upper radiator hose. And I installed an HVAC fan-cycle switch on the high pressure refrigerant line access fitting. Wired that into a relay so when the refrigerant head pressure went past a certain setting, the fan would kick on. A bit extreme but hey, I was an HVAC tech at the time. And if the head pressure was low enough (defrost setting during winter) the fan would stay off. Helped the car warm up faster in the cold.

When the '92 Sport was a daily driver, I didn't have much of a highway commute. And it was always fun to blast down the winding back-roads home. So I never noticed the running fan restriction until I made a 50 mile highway trip. Thought about a bypass switch to shut it off manually but I'd like to try something automatic.

[Allan]

91 XR7, That Painless setup looks nice. Might be cheaper to swap ECU's though.

[Allan]

bowez, tapping the VSS sounds like a good idea. I'm not too EEC savy so I'm not sure what I would do with it. Another research project for me.

You have an SC. What do most of the guys do about fan control when they swap to a 5.0? I assume they are swapping in one of our 5.0 ECU's so they have to run the fan from an aftermarket controller like I am.

[bowez]

I'm thinking just use the stock CCRM which if the 5.0 has the connector would be the easiest solution .

I might try and take some measurements this week probing the VSS signal.

At $250 I'd ignore the painless system.

[91 XR7]

heh $250?? my god, never knew.. i just learned about it two days ago and never looked into it that far

Also Wonder if you can get a MSD window switch kinda thing to do the job?? I'm thinking if the signal can be register in the module that it can be Programed to turn off the cooling fan..

[Allan]

You know, I don't even remember where the CCRM is on the Sport. Probably in front of the air cleaner, but I don't think I was aware of its existence when I installed the fan. I learned about the CCRM when I got my '92 SC (cutting the #14 wire, using Dave Neibert's fan controller wiring, etc.). I don't have EVTM's so I'll have to see what's listed in the Haynes or Chilton wiring diagrams.

I should get a second adjustable fan switch so I can actuate the low speed instead of just the high. This way I'll keep from burning out relays and wires by always starting in high.

[Allan]

Also Wonder if you can get a MSD window switch kinda thing to do the job?? I'm thinking if the signal can be register in the module that it can be Programed to turn off the cooling fan..

Figured there's got to be something switched on or off at a higher speed that could be used to actuate a relay. I'll look into bowez's cruise control suggestion. I might just switch to a 94-95 GT or Cobra EEC. At least with the Cobra unit I could upgrade to 24Lb. injectors. But I might have to swap CCRM's too.

Next weekend I should be able to get to the car to poke around under the hood.

[bowez]

The main issue with the CCRM is it is receiving a switched ground from the EEC, but if you have the harness then I would assume the function is already there.

[94 Daily Driven 4.6L]

Just my .02, but I would install an small (maybe 4” x 4”) air vane/flap somewhere in front of the radiator (or a good place where there is good airflow) and have the vane open a NC switch that is in series with the ground side of the relay for your fans. It just has to be far enough away that the electric fan doesn't suck it back disabling the fan...

It would take a little trial and error to get the vane’s spring tension correct and where to adjust the switch, but it should be relatively simple. Same principle as VAF systems, but rather than looking to meter, just set for closed/open. And it could be mounted anywhere there's good airflow.

Basically, any time the air flow (pressure) forces the vane back to a set position; it opens the switch disabling the fans. When you slow down and the air flow on the vane decreases a spring pulls it forward, and the switch closes enabling the fan system. It would be directly dependant on vehicle speed, but independent of any electronics, VSS, etc..

Ok, so if you’re sitting at a stop light and have a 50 mph headwind your fans might not work.

Basically something like this, but more customized


I’m lazy and like things simple.

[Bradone]

Originally Posted by Allan

Although my aftermarket temp switch works well with my electric fan, I'd like to find a way to automatically disable it over 40 mph. My coolant runs cooler with the fan off at highway speeds.

The MN12's that come stock with electric fans have EEC drivers that control fan operation. Our 5.0 cars don't have any electric fan or its controls. I've thought about doing MadMartigan's Mustang ECU swap because it can control high and low fan speeds. Just not sure what else would be needed to make the fan part work (adding wires or rewiring the EEC fan outputs or adding an ICRM, etc.).

Any ideas besides EEC swaps?

-Allan

I did the EEC change. It is pretty much plug and play except you need to disable Pin #30 (clip the wire and move the female pin connector to #55 in the TBird harness). I used 2 40amp relays from Radio Shack and a 6 connector block. See pictures:

http://s204.photobucket.com/albums/b...Fan%20Install/

You will need to run the wires up through the fenderwell. Underhood you will need the main power (I used a 60amp Maxi Fuse and 6g wire) and a key on 12v supply lines. Using the wiring block made it easy. We built it on the bench and it gave an easy mount for the diodes. Total parts were only about $25 (excluding MAXI fuse).

As to the PCM switch, if you are not going to tune don't even think about it. The stock (94/95) GT (T4M0) does not even turn the low fan on until 204* and the Cobra (J4J1) does not turn it on until 208*. High speed fans don't come in until 220*. The tunes are "PIG" rich to counter this. I have been told this was to fuel the cats of the time. Though I realize this was the way at the time, it is not necessary today. I run 180* thermostat and bring in the low fan at 184* and my high speed on at 196*. I shoot for the 180-190* area. You can run a much crisper tune AFR wise at this temp range. Sorry for getting off subject.

Good luck
Brad

[bowez]

VSS signal at 40mph is 3.5v AC and 8Hz.

I'll try and come up with a circuit but if anyone want to help I'll gladly accept.

[David Neibert]

I don't see how the radiator is going to flow more air with the fan off. For that to be true, the air blowing through the core would have to be moving fast enough to make the fan blade spin faster that it would normally with the electric motor running. Not likely at 40 mph or even 80 mph.

The electric fan will move alot more air when being force fed from the high pressure area in front of the moving car, than when sitting still and having to pull all the air through the radiator core.

David

[bowez]

I have a design that will shut off the fan a ~40mph using the VSS if any one is interested. I still need to do prototyping.

If there is interest I can even have the fan come on at a predetermined temp--using the stock Engine coolant Temp sensor.

[Allan]

Don - The thing I miss most about HVAC work is being surrounded by the engineering controls manufacturers use, either on OE equiptment or retrofit devices. You get alot of ideas that can work for automotive purposes. Although I've installed many sail-switches and differential air pressure devices on gas-burner retrofits, I never thought to use one for this purpose. Thank you for the idea.

If I can't do it through the VSS, I'll try this. A local Grainger or Johnstone Supply catalog would have a switch that I could use. If I wanted to reinvent the wheel, I could also use a delay-on-break relay to keep the fan from short-cycling. Good stuff.

[Allan]

Brad - Good info on the EEC swap. I saved a copy of your switching diagram. As far as the PCM switch control for fan temps, the Super Coupes have a similar high temp turn-on. On SCCoA there has been a diagram around for years that enables you to use two relays and two aftermarket adjustable fan temp controls to set the high and low speeds for whatever temp you want. I think this might be David's diagram. It has the benefit of still allowing EEC control if the AC comes on or let's say, an adjustable switch fails in open position. It also allows the fan to shut off at speed. So I figured I would still need to wire the adjustable setup from my old SC.

[Allan]

Bowez - Is it an indepedent circuit or does it work with EEC logic?

If I can find it, I came across a circuit that uses two IC's to control high and low fan speed as well as high vehicle speed shut-off. It had hookups to the VSS and wires 14 & 17. When I find it I'll post it. Ironically, I believe I found it on a Mustang site dealing with swapping SC engines. Thanks.

[Allan]

I don't see how the radiator is going to flow more air with the fan off. For that to be true, the air blowing through the core would have to be moving fast enough to make the fan blade spin faster that it would normally with the electric motor running. Not likely at 40 mph or even 80 mph.

The electric fan will move alot more air when being force fed from the high pressure area in front of the moving car, than when sitting still and having to pull all the air through the radiator core.

David

David - I thought that the SC fans shut off because of restriction. If that isn't the case then maybe it was done to keep the fan from over-speeding or over-amping? Possibly 40 mph was enough although not ideal for highway cooling so the fan would last longer by turning it off? I guess there must have been some reason for the factory to set it up that way.

I probably have another cooling issue(s) if I'm the only one seeing this problem.

Out of curiousity, does anyone get there cars tuned so that the cooling fans stay on at higher speeds or with no high speed shutoff?

Thank you everyone for your info. When I get out to the Sport I'll check the obvious stuff first (air dam integrity, fan wires, etc.). I'll let you know what happens or what I find.

-Allan

[Velocityx7]

I found this :http://www.dakotadigital.com/index.c...rod/prd460.htm, you could simply use it to trigger the fan relay at a set speed! The only problem I see is turning it back on when you drop below 40MPH. If nothing else you could contact them and see if they have an idea.

[94 Daily Driven 4.6L]

Originally Posted by Allan

Don - The thing I miss most about HVAC work is being surrounded by the engineering controls manufacturers use, either on OE equipment or retrofit devices. You get a lot of ideas that can work for automotive purposes. Although I've installed many sail-switches and differential air pressure devices on gas-burner retrofits, I never thought to use one for this purpose. Thank you for the idea.

Yep. My best friend is a guy who designs/installs/troubleshoots control systems for large power generation systems (gas turbine, geothermal, diesel, hydro, etc.) and we're always comparing technologies between industrial and automotive applications. (Sorry bastard travels the world doing all this stuff as a private contractor.. )

It is amazing how similar all the technologies are and how they can be adapted between the two.

Let us know what you finally decide to do.

[bowez]

My design is totally independent of the EEC all you need is the VSS.

[David Neibert]

Originally Posted by Allan

David - I thought that the SC fans shut off because of restriction. If that isn't the case then maybe it was done to keep the fan from over-speeding or over-amping? Possibly 40 mph was enough although not ideal for highway cooling so the fan would last longer by turning it off? I guess there must have been some reason for the factory to set it up that way.

I probably have another cooling issue(s) if I'm the only one seeing this problem.

Out of curiousity, does anyone get there cars tuned so that the cooling fans stay on at higher speeds or with no high speed shutoff?

Thank you everyone for your info. When I get out to the Sport I'll check the obvious stuff first (air dam integrity, fan wires, etc.). I'll let you know what happens or what I find.

-Allan

Allan,

I've had that 40 mph shut off feature disabled for many years and the fans operate strictly on coolant temp now. I'm using a pusher and a puller fan with griffin radiator on both my cars.

David

[91 XR7]

Originally Posted by bowez

I have a design that will shut off the fan a ~40mph using the VSS if any one is interested. I still need to do prototyping.

If there is interest I can even have the fan come on at a predetermined temp--using the stock Engine coolant Temp sensor.

I'm just curious has to what you designed, So i'm interested

[Allan]

David, thanks for the response. I'm planning on adding a second fan switch to switch on the unused low speed and continue to use high speed, both without any high mph shutoffs.

Found that I need to resecure the flexible air dam going from the radiator support to the front crossmember. I need a new front air dam. I guess there will be better highway cooling if I get some air to the radiator!

Bowez and 91 XR7, this is the adjustable fan circuit that uses the factory ECT. I don't know where exactly I found it, but it is from a Mustang site. Haven't tested or even built it yet. I'm not sure if it will work, but somebody spent some time drawing it up. For your enjoyment:

http://forums.tccoa.com/vbpgimage.ph...7&d=1281244807