A3 Fan Clutch

[B25Truck]

Gentlemen,

Our A3 was in a parade over the weekend (got lots of cheers as we drove by) but the only way to keep it from overheating was to open the side doors on the engine compartment and turn the heater on.

Figured it was the fan clutch or the actuator. With engine running the fan was no where near turning as fast. Freewheeling. And with engine stopped you can turn the fan by hand.

So I went looking here and have seen both answers: Air pressure locks the clutch and no air pressure locks the clutch.

Before i start taking things apart which is correct?

Thanks

 

[rustystud]

Almost all Air-Operated fan clutches use air pressure to "Apply" the clutch. Most air clutches have drilled and tapped holes to put bolts in, in case of loss of air-pressure. There are some air operated fan clutches that use air pressure to "release" the fan (Bendix/Kysor) but mostly Cat has used "Horton" fan clutches which are all air applied. Just to be sure check what make of fan clutch you have on your engine.

 

[Floridianson]

You would think in military application we would want no air then the fan is engaged. Air pressure then would disengage. Now the fan on my MTV 3116 Cat is like that it takes air to disengage so it is locked up till the air comes up in the truck. One would think if there was a problem in the field we might not want or be able to stop to put bolts in or make repairs. Get out of Dodge thing and not over heat thing. Been awhile for me working on the Deuce A3 but I believe it is air to disengage. You can check you shutter stat or just add air to the line that runs to the fan. The system can be set up ether way. If the shutter stat is N/O then the clutch would disengage when the air came up when the clutch is set up for that way. If N/C then it would in gage when the Temps went over the set point of the shutter stat or Temp. switch and the clutch was set up that way. My M920 was set to lock up without air and disengage with air because someone set up the shutter stat and fan clutch that way. You have to set up both shutter and clutch one way or another or they have too match.
If someone stuck a N/O where there should have been a N/C shutter stat or switch or N/C where it was called for N/O it would drive you crazy till you checked both shutter/switch and fan to see if they matched.

 

[B25Truck]

Thank you
Guess I'll be doing some digging this weekend.

 

[rustystud]

You would think in military application we would want no air then the fan is engaged. Air pressure then would disengage. Now the fan on my MTV 3116 Cat is like that it takes air to disengage so it is locked up till the air comes up in the truck. One would think if there was a problem in the field we might not want or be able to stop to put bolts in or make repairs. Get out of Dodge thing and not over heat thing. Been awhile for me working on the Deuce A3 but I believe it is air to disengage. You can check you shutter stat or just add air to the line that runs to the fan. The system can be set up ether way. If the shutter stat is N/O then the clutch would disengage when the air came up when the clutch is set up for that way. If N/C then it would in gage when the Temps went over the set point of the shutter stat or Temp. switch and the clutch was set up that way. My M920 was set to lock up without air and disengage with air because someone set up the shutter stat and fan clutch that way. You have to set up both shutter and clutch one way or another or they have too match.
If someone stuck a N/O where there should have been a N/C shutter stat or switch or N/C where it was called for N/O it would drive you crazy till you checked both shutter/switch and fan to see if they matched.

I was thinking about that last night after I wrote that last post. In todays vehicles with "Automatic fire suppression systems" you must have air apply. That way if a fire starts you won't be "fanning the flames" when the fire burnt through the air lines as it would go full force on. Well if he has a "Horton" then we know it is air apply and if it's a "Bendix/Kysor" then it's a air release.

 

[B25Truck]

Mystery solved: Air needed to release. Actuator has Kysor on it and with the injection of a drop or two of MMO (Marvels Mystery Oil, great stuff) actuator now appears to work. While still freewheels, feels 'looser' if air applied.

Read basic TM's for replacement and basically boils down to 1) remove brushguard, 2) remove radiator, 3) replace/rebuild clutch, 4) reassemble

Anybody ever done this without removing radiator?

 

[rustystud]

Mystery solved: Air needed to release. Actuator has Kysor on it and with the injection of a drop or two of MMO (Marvels Mystery Oil, great stuff) actuator now appears to work. While still freewheels, feels 'looser' if air applied.

Read basic TM's for replacement and basically boils down to 1) remove brushguard, 2) remove radiator, 3) replace/rebuild clutch, 4) reassemble

Anybody ever done this without removing radiator?

Don't try it. It's not worth the cost of a radiator just to save a few steps and a little bit of time.