Mishimoto cooling fans

[71-73modstangs]

ok,just bought the mishimoto dual cooling fan set up. I'm going to run these in an 04 gt. If I've done my research correct,The oem CCRM has a relay to control the fan during normal operation(low speed) and one for when a/c is on(high speed). So,the oem single fan runs at 2 speeds. In which I'm assuming voltage must be cut down a bit during low speed operation by that little resistor/speed controller mounted up top of the oem fan shroud.
Since I'm using two fans,should I seperate one fan for low and the second for high. Or should I parallel them together and use that little resistor/speed controlled from the oem fan? My only problem with that is,I'm not sure what the output or cfm would be on these fans is the voltage is cut below 12.5v. They may not even come on at anything much lower. however,If I seperate the fans,will a single fan do the job when the a/c is not running. Or does the fan speed get controlled by engine temp differences. I have heard that the fan comes on at 190 degrees at low speed and kicks up when engine reaches 218 degrees or something. If thats the case,then I'll seperate them. any info appreciated!

 

[wmburns]

Your understanding is NOT completely correct.

The GT/Cobra does use a two speed fan. It does this with a tap on the fan motor itself. The CCRM sends +12 volts to the RD/OG wire for the LS mode. For HS mode, +12 volts goes to the OG/LB wire. Ground is via the BK wire.

The PCM selects the LS speed fan at a certain coolant temperature. As the temperature rises above a certain higher point, the HS fan is selected. The temperatures quoted in the OP seem about right.

The LS fan goes through an aux circuit breaker with a lower amp rating. If the high speed fan is run through the LS circuit, this breaker will trip.

The PCM ensures that either the LS or HS fan is runnng all the time the AC is on AND the car's speed is less than 45 MPH. Above 45 MPH, the fan shut off completely. So it is not completely true that the HS fan is forced when the AC is on.

If you tie the LS and HS together, this will feed back through the other circuit. The idea of installing a ballast resister depends upon if the circuit kills power to the LS leg when the HS is selected. Which is a detail I do not know.

I suggest that you disconnect the fan and find out if power is seen on the other connector when the fan is in either LS or HS mode. This will determine the best way to adapt the circuit to work.

Consider that if one fan is simply connected to the LS circuit and the other to the HS circuit, then one fan will run in LS mode. When the PCM switches to HS mode then one fan may stop and the other start working. This will result in the same amount of air flowing and an eventual over heat.

If both fans are wired to the LS circuit, then both will run when the PCM calls for LS fan. But when the PCM calls for HS fan, then BOTH fans will shut off. Overheating will result.

If both fans are wired to the HS circuit, the neither fan will run when the PCM call for LS fan. This will result in high head pressure to the AC compressor. There is a back up circuit that would force HS fan, but this will cause the AC pressure cycle between high head and low head. This will shorten the life of the compressor and reduce the cooling inside the passenger compartment.

If you would like some help with this, the results above will be needed.

Why are you doing this swap? Are you having overheating problems?

 

[71-73modstangs]

well,here is the deal,I have the 4.6 2v going into an older stang. I bought a mishimoto aluminum radiator for the 95 stang because it fits better and wanted the filler cap on the radiator. The 99-04 radiators use that sealed system that requires filling the system through the reservoir on top. I didn't want to bother with all that. They also offered a dual cooling fans with aluminum shroud for that radiator so,I bought it because I liked they way they looked. I am running all the oem wiring,ccrm,pcm,etc from the 04 mustang gt so,right now,I'm trying to figure out how to wire these fans. The oem single fan,has three wire connection,the RD/OG Wire coming from the ccrm,connects to some kind of resistor/coil etc. mounted on the top of the shroud,before heading to fan. I'm not sure what that does. It doesn't show anything in my wiring diagram about it. I assume its cutting the voltage in LS mode to create a slower fan speed.

I guess my options are to use sell these and use oem fan. Or,I could bypass all the pcm and ccrm controls and use a stand alone setup. Use a derale dual fan thermostat controller which also controls fans during a/c use. I would probaly have to run a seperate relay,using the clutch engage signal to trigger the relay to cut on fans. But,not sure how the pcm will react if the oem fan is unplugged. Its may have some failsafe that won't allow a/c to work if,fans are inoperative.

 

[wmburns]

You didn't answer the question about how the CCRM works and selects between the two modes and how it presents to the fans. I am confused by your reply because it seems to indicate there is only one wire from the CCRM while I am confident the 96-04 GT has two. See the attached wiring diagram.

Just wondering. Based upon my original reply, how would you access my electrical knowledge?

If I asked for it, could you supply the power requirements of the fans? This information would be needed to compute the wattage of a ballast resister.

Do you have a preference on how you would want the fans to work? For example, have one fan kick on LS mode and both on HS mode? Or have both fans run slower in LS mode?

If you needed to add some external diode or relay to prevent feedback, could you wire it in?

I do have an 2003 and a 2000 Mustang and may be able to answer the questions by experiementing on my own car. I am just not sure I will be able to get around to it.

When did you plan on wiring this up?

 

[71-73modstangs]

I guess the real question is,does the LS circuit cut off when HS circuit is engaged? you look at acual fan shroud in the car,there is a 3 wire(LS+,HS+,Ground) connection for the fan. The device I'm talking about on the fan shroud contains a ballast resistor and fusible link. The link will open if the resistor overheats, and resets when it cools. This component is not shown on the wiring diagram because its considered part of the fan assembly. Its mounted inline between the LS+ wire(RD/OG) and the fan motor. Each LS and HS relay inside the ccrm gets their own seperate signal fron the pcm. If the LS mode is triggered by a lower temp and HS triggered by a higher temp,you would think the LS mode would continue to stay hot until temp comes back down.
Problem is,I am building a car with parts from another car so,I can't just turn a key on and check wire voltage,etc. If you get a chance to check your car out,let me know if the LS+ wire switches off when HS+ wire is engaged.
I would like one fan to come on during LS mode and both during HS mode. So,I think I'll use RD/OG Wire to one fan and OG/LB wire to to second fan and do away with the ballast/resistor. If you look on mishimoto website,they have an aluminum shroud,single 14" fan for the 99-04 gt mustangs. The cfm's are 954.5 at 12v,which means cfms will be alot less during LS mode. so,if thats enough to cool the 99-04 gts,then these 12" fans rated at 933.5 cfms each,should be fine in LS mode and more than enough at HS mode. Now,if the LS fan turns off when HS fan turns on,then I'll have to run HS leads to both fans to trigger both during HS mode. But,that would require diodes on both fan hot wires to keep power from running back into the ccrm,correct?
EACH FAN:
CFM: 933.5
Fan Diameter: 280mm
Fan RPM: 2095
Number of Blades :10
Current: ~8A
Volts: 12.25V
Amps: 5.7
Velocity Ft/Min: 724
Inlet Pressure While Tested: -0.04
Air Temp While Tested: 62.6 (degrees F)

 

[wmburns]

I been thinking about this and believe this will work based on the numbers posted. I have done some tests so that I know there is natural feed back from the fan motor itself. So it is not necessary to prevent back feeding the CCRM.

Go to Radio Shack and get:

6A, 50V Rectifier Diodes (4-Pack) Model: 276-1661| Catalog #: 276-1661 $2.49
http://www.radioshack.com/product/index.jsp?productId=2062591

Each diode supports 6 amps. We will need to parallel 2-4 together to get enough current carrying capacity. 2 would give 12 amps which should be enough to run one fan.

It may be possible to find some larger diodes with greater current capacity. But this should provide a proof of concept.

From the LS wire, go directly to a single fan. This is the fan to run while in LS mode.

From the HS wire, go directly to the other fan. This fan will run in HS mode.

Now here’s the tricky part. Use the diode group to jump between the HS and LS wires. The diode band will need to point towards the LS fan. The diode will prevent the LS current from back feeding the HS fan when only the LS fan is called for.

However, when the HS fan runs, the DC power will flow from the HS side to the LS side allowing both fans to run when HS fan is called for.

There may be a problem with diode heating. Perhaps consider spreading the diodes out to cool. Or stagger the units so that they do not touch. Again some testing under load should be done.

This can easily be bench tested using a battery charger (or battery) to drive the fan. In this way it would be possible to test without having to install on the car.

This could also be done with a simple 12 volt relay.

If the proof of concept works, consider getting diodes in a different packaging. Higher current carrying capacity is possible. Some packing may even have mounting tabs that will help in fabricating a mounting method.

Does this make sense?

An alternative is to tie both fans together and run directly to the HS wire, Get a suitible high wattage resister and insert between the LS wire and the two fans wires. This will make both fans run slow at LS and fast at HS.

This may require some expermination to get the resister size. We know the current draw (16 amps total) but we need to know what the target voltage/amp at the fans to get the desired motor speed. If we guess reducing the current by half, then the resister needs to be about 0.75/1 Ohm. The resister would need to have a fairly high wattage rating.

For a proof of concept, the following might work. It's only $2. However, it may not have enough wattage.

http://www.radioshack.com/search/in...s&filterName=Type&filterValue=Power+resistors

Disclaimer, I have no idea if this will give a reasonable speed in the LS mode. Experiment!

 

[71-73modstangs]

Thanks for taking the time to help figure this out....
One more question,you said here.......

"Use the diode group to jump between the HS and LS wires. The diode band will need to point towards the LS fan. The diode will prevent the LS current from back feeding the HS fan when only the LS fan is called for. However, when the HS fan runs, the DC power will flow from the HS side to the LS side allowing both fans to run when HS fan is called for."

Now,this would only be required if the LS mode turns off when HS mode turns on. If I insert a diode between the LS and HS wires to operate both fans in HS mode,shouldn't there also be a seperate diode on the LS wire pointed towards the fan,to keep feedback from going back through LS wire to ccrm during HS mode??

 

[wmburns]

Recall that I stated "reverse feedback through the CCRM is NOT an issue". The reason? Because it happens all the time naturally.

On my 2000 or 2003, if the fan is in LS mode and a test is done on the HS side, the tester will show +12 volts. It comes from the fan motor itself.

The reverse is also true. In HS mode, a test of the LS wire will show voltage from the fan motor.

So, the back feeding of the CCRM doesn't make any difference.