has anyone figured out how to turn the engine fan on in the 2005 ctd, its computer controled, there should be a way, really need it when backing a trailer.

 

Were it is controled by the computer. It will come on when it needs to. I wouldn't worry to much about it. Unless it is overheating.

 

at what temp does the fan come on anyway

 

Turn the AC on and see if it comes on.

 

If I sit at a stop for more than a couple of seconds the fan comes on. Temp is under the 200* mark on the gauge also.

 

On my 05 2500 ctd it appears to be a thermostatic fan clutch that ingages. (IMO) Although I havnt spent time looking at it, it would be really interesting if it was a electronic or computer controlled clutch. From what I have seen when the AC pressures start to rise after turning on the AC it is not acting like a computer controlled clutch in that it will engage after the condenser temp. has risen to over 200 deg. ( or will burn the heck out of your hant if you touch it) . Instead of when the pressure reaches a set figure. Like many vehicles I have seen with ecm controlled electronicooling fan. These trucks have amazed me and disapointed me ( like the lift pump issue or the blend door problems) while the engine is so well made and the over all design is great. Anyone know the design and all?

 

You have an auto, don't you?

 

I have a 30 ft. camper that weighs around 8500 lbs. that I had the same problem with when backing up . I read a thread that said to put it in 4low and it would help with overheating. I had to back up my camper yesterday in 100 plus heat and it didn`t heat up at all, plus it backs up an incline much easier. Hope this helps .

 

Not sure on a 2005 but the Light Blue with White stripe on a 2004 sends +12v to the viscous fan clutch.

Go to http://www.hemitruckclup.com download the 2005 shop manual, and find the wire color for a 2005.

Setup a switch and relay to send +12v to that wire. Or use the reverse light voltage to fire the relay and omit the switch.

 

The fan clutch has a ignition switch on +12v. The fan speed is controlled by the ECM using Pulse Width Modulation. That's the wire that needs to be tapped for fan speed. But a diode will be needed to to protect the ECM from the voltage backdrive when the fan speed control is being powered from another source.

MikeyB

 

This is what I have been wanting to do since I bught mine. Remember, Its easier to keep an engine cool than it is to try to cool it down. Dont let it get too hot and you should be able to keep it from getting hot, unless there is something wrong.

I would love to have manual control of the fan. The class 8 trucks have the fan switch so they can turn them on before a hard pull and when running at high idle while sitting still. That is just what I need to be able to do with mine and when some one figures it out let me know.

 

Why not install a electric pusher fan in front of the condenser? Be Cool 16" Thin Line will fit between the grill and condenser. You can have the fan controlled by a thermostat or just manual control depending how you setup the fan.

MikeyB

 

Why spend the money on a pusher fan when I have a very nice factory fan that I can set to come on at my demand and will only cost me a few bucks?

 

I'll have to admit the shop manual is confusing. According to the wiring diagram the fan clutch is getting either +12v or nothing through the condenser fan relay. However, according to the verbage it implies the fan is variable speed and electronically controlled. So putting 2 and 2 together the fan clutch is probably activated by both heat and an electric clutch. The ECM knows the fan speed through a speed sensor and I assume it just switches the relay on/off in relatively rapid sequence to get the speed it wants (to compensate for the heat-activated portion of the clutch).

Using that logic, if you send +12v down the Light Blue with White Stripe wire (on a 2004) you'll get the electric clutch fully engaged but the fan will spin according to the heat portion of the clutch?

Again, according to the manual, the fan clutch gets its power through a relay and the relay gets it's power source directly from a 30 amp fuse (+12v) and there are only 2 wires going to the fan clutch.....the +12v wire and a ground wire. That means it's either getting +12v or it isn't.

Any DC engineers out there know if the fan is modulated in a different manner?

Lacking any proof that the fan is modulated in a different manner, you can send +12v down that wire and you'll have full fan (depending on the viscous portion of the clutch).

 

Our Macks use the same style electronic viscous fan clutch and it works something like this. There is a speed sensor inside the fan clutch that monitors speed of the fan in relation to the drive hub. It uses ambient air temp, engine coolant temp, and ac head pressure and adjusts the speed accordingly. It adjusts the speed by means of restricting and allowing viscous oil to flow into the clutch portion of the fan clutch. It gets its variable speed ability by how much fluid that it allows in. If you look at the plug at the bottom drivers side corner of the radiator I think you will see there are about 5 wires going to the clutch, If its like the BEHR clutches on the Mack.

Which relay is the fan clutch relay and I will jump it to see if I get full lock up.
It should be pins 87 and 30 if its like all other relays???