Radiator Coolant Fan Runs All The Time

[GlennLever]

Noticed my hydraulic radiator fan is running all the time.

Gillig tells me that there is a sensor to control the fan solenoid.

Gillig sent me a circuit diagram for a 1994 bus with rear battery box an run box (I am a 1996 chassis for a 1997 Motor Home)



The color codes on the wires at the fan solenoid are not correct.



If I feed 12V and ground to the fan solenoid the fan slows down right away, remove the 12 v and it speeds up.

This is the fan solenoid



It control hydraulic pressure to the fan



Gillig supplied the sensor location.



Wire color codes are correct here. But the wires leading into the harness at the fan solenoid are different.

If I supply 12v to the yellow and ground to the black nothing happens.

Ok, I have heard back from Gillig with a new diagram.

Color codes on this diagram are correct.

There is an additional sensor between the coolant temperature sensor and the fan solenoid. (Air Inlet Fan Temp REF 51-15885-000)



I have asked the parts guy, Rick, to give me the location of this sensor, and part availability?

I suspect that as a temporary fix I could tie the Yellow and Red wires running into the Air Inlet Fan Temp together (no cutting, I have the weather pack connectors and can make a shut plug).

The fan should then operate as depicted in the earlier circuit diagram.




I could get this done before the trip to Bowling Green and install the part when I return.

I would feel much better with this working correctly.

I believe this symbol is for a diode, but have forgotten how to read it, I believe the current flows in the direction of the arrow inside the symbol??? Help??? That does not make sense as as there are arrows pointing in both directions.

[Ivylog]

In the second diagram of your first post there is no inlet temp sensor and with your jumper you are back to that design... so yes it will turn on the fan when the engine temp gets high enough... assuming the engine temp sensor is not faulty. Thanks for the update.

PS: I'm not just another pretty face.:B :B :B

[GlennLever]

Ok...I'm sure everyone is waiting with batted breath.

I did find the Air Inlet Temperature Sensor



and it did have the correct color coded wires.

I have said this before, I love weather pack connectors, you can make up what ever you need, they can be taken apart and rebuild another way. In this case I needed to connect the red and yellow wires to test if the Air Inlet Temperature Sensor was the problem.

This is the shut plug I made up.



And now for the test, I fired up the engine with the sensor unplugged, the fan ran full speed, I plugged in my shut plug and the fan slowed right down.

Success.



So now is the question will the fan run up to speed when the coolant reaches 195?

Strangely enough I cannot answer that.

I ran the engine at 1,500 RPM for 30 minutes and the temperature gauge never went above 170. I let it run while I greased every grease fitting under the Motor Home, still never went above 170. I loaded the Motor Home with stuff for our trip to Bowling Green, still did not go above 170.

I took the Motor Home for a drive all the way around the outer loop of Rochester (30 miles) still did not go above 170.

I started to suspect the gauge was bad, drove to my home and got an infrared heat gun, and went all over the engine. The highest temperature I got was 175.

I have said in the past this radiator and fan are huge. Apparently on a 75 degree day the fan running at slow speed moves enough air to keep the engine cool.

The real test will come when we drive to Bowling Green pulling the trailer.

It is a simple fix to get the fan to come back on if it does over heat, just remove the shut plug.

[Bend]

Flyback diode - used to protect electronics powering DC motors, +:

https://en.wikipedia.org/wiki/Flyback_diode

[K_Charles]

When you drop power to a magnet, the magnet produces a voltage that backwards to the voltage that was energizing the magnet. Not much but still enough to make funny things happen in other places. We used diodes a lot in construction equipment also.

[Ozlander]

It's common to have diodes across relays and solenoids for spike suppression.
On aircraft, all relays, big and small, will have a diode across them.

[GlennLever]

Vulcan Rider wrote:

GlennLever wrote:

I agree, to me the diode does not make sense, why is it there?

The way the diode is drawn is non-standard but I think the only "arrow" that counts is the big one in the middle.

Then......the fan probably is supposed to run all the time that the A/C is ON.

And even if it is running all the time, sometimes when it doesn't need to, that should NOT be a problem unless you are driving in VERY cold weather.

The motor home has a separate electric fan for the A/C and it runs whenever the A/C clutch is engaged.

Ivylog wrote:
In the drawing of the engine it shows a sensor in the side of the pipe (intake air after the turbo) near the intake manifold of the engine. If it has three wires (R, G, Y) then that's it. On that vintage engine the turbo boost is a tube running to the back of the injection pump, not an electric sensor.

Fantastic eyes, I never saw the sensor in the top left corner of the drawing, I will check it THANKS

[Ivylog]

In the drawing of the engine it shows a sensor in the side of the pipe (intake air after the turbo) near the intake manifold of the engine. If it has three wires (R, G, Y) then that's it. On that vintage engine the turbo boost is a tube running to the back of the injection pump, not an electric sensor.

[Vulcan_Rider]

GlennLever wrote:

I agree, to me the diode does not make sense, why is it there?

The way the diode is drawn is non-standard but I think the only "arrow" that counts is the big one in the middle.

Then......the fan probably is supposed to run all the time that the A/C is ON.

And even if it is running all the time, sometimes when it doesn't need to, that should NOT be a problem unless you are driving in VERY cold weather.

[GlennLever]

Ivylog wrote:
The good news is it's not a Sauer Danfoss controller... $$$. I believe your sensors are normally closed so you get 12V to the fan solenoid which slows it down until needed. Looks like the air inlet temp sensor keeps the fan off when cool air is coming into the engine intake so bypassing it should not hurt anything... in fact I'm not even sure why it's needed. The Sauer Danfoss complicated system only senses engine temp which is what you've done in the last diagram.

*At some point (first diagram) they did not feel the need for a air inlet temp sensor. I do not think you need one now but if it's a reasonably price sensor... why not as it may sense the need for more cooling sooner than the engine temp sensor.

I agree, to me the diode does not make sense, why is it there?

I suspect that as a temporary fix I could tie the Yellow and Red wires running into the Air Inlet Fan Temp together (no cutting, I have the weather pack connectors and can make a shut plug).

Any idea where the sensor would be. The red wire goes into a harness at the rear that is about two inches in diameter, I have traced it across the rear of the engine, but then lose it.

[Ivylog]

The good news is it's not a Sauer Danfoss controller... $$$. I believe your sensors are normally closed so you get 12V to the fan solenoid which slows it down until needed. Looks like the air inlet temp sensor keeps the fan off when cool air is coming into the engine intake so bypassing it should not hurt anything... in fact I'm not even sure why it's needed. The Sauer Danfoss complicated system only senses engine temp which is what you've done in the last diagram.

*At some point (first diagram) they did not feel the need for a air inlet temp sensor. I do not think you need one now but if it's a reasonably price sensor... why not as it may sense the need for more cooling sooner than the engine temp sensor.

[Dick_A]

Current flow is against the arrow i.e., electron flow through the arrow of the diode to ground.