Hydraulic Fan Control - ‘99 Affinity

[Aroadracer]

I have a '99 Affinity with the Cat C12 motor. I'm trying to understand if my hydraulic fan is operating correctly or not as I have the classic dust cloud under the rear when driving on dirt roads.
Here is what I know:

The system has a Sauer Sundstrand thermostatic wax valve in the radiator in series with a Sauer Sundstrand two wire solenoid valve which control fan speed.
At idle, the fan turns approximately 780 RPM.
There is no power to the solenoid, even with the over the road AC on. (5 amp fuse may be blown but don't know where it is located).
If I jumper 12volts to the solenoid, the fan RPM drops to 190 RPM.
At this point, I don't know if the fan speed increases with either temperature or engine rpm.

My questions are:
1. Can someone explain how the system is supposed to operate?
2. What is the expected fan RPM at idle?
3. What is Max fan RPM?
4. What is the purpose of the Hydraulic solenoid?
5. where is the 5 amp fuse that is in the hydraulic solenoid circuit.

thanks,
Jim

[Ljwt330]

Originally Posted by Aroadracer

I have a '99 Affinity with the Cat C12 motor. I'm trying to understand if my hydraulic fan is operating correctly or not as I have the classic dust cloud under the rear when driving on dirt roads.
Here is what I know:

The system has a Sauer Sundstrand thermostatic wax valve in the radiator in series with a Sauer Sundstrand two wire solenoid valve which control fan speed.
At idle, the fan turns approximately 780 RPM.
There is no power to the solenoid, even with the over the road AC on. (5 amp fuse may be blown but don't know where it is located).
If I jumper 12volts to the solenoid, the fan RPM drops to 190 RPM.
At this point, I don't know if the fan speed increases with either temperature or engine rpm.

My questions are:
1. Can someone explain how the system is supposed to operate?
2. What is the expected fan RPM at idle?
3. What is Max fan RPM?
4. What is the purpose of the Hydraulic solenoid?
5. where is the 5 amp fuse that is in the hydraulic solenoid circuit.

thanks,
Jim

Here is a generic explanation of how the system should operate. The specifics of min/max rpm may not be exact but the relative changes are clear.

The purpose of the solenoid and wax valve are explained as well.

https://www.centralstatesbus.com/wp-...s/a3hydfan.pdf

[Aroadracer]

Thanks Larry, that is a good explanation on operation. Now if I can find out why the solenoid is not engaging, that should fix it. My CC schematic does not make sense as it has the solenoid controlled by power to the ac clutch and fan relay. It makes more sense to be controlled by a charge air temperature sensor. I do know that the fan speed drops when I manually energize the solenoid (when cold) and that agrees with the Blue Bird manual.

[Ljwt330]

Originally Posted by Aroadracer

Thanks Larry, that is a good explanation on operation. Now if I can find out why the solenoid is not engaging, that should fix it. My CC schematic does not make sense as it has the solenoid controlled by power to the ac clutch and fan relay. It makes more sense to be controlled by a charge air temperature sensor. I do know that the fan speed drops when I manually energize the solenoid (when cold) and that agrees with the Blue Bird manual.

There is logic to the solenoid being wired to the A/C clutch and fan relay. If the A/C is turned on and there is inadequate air flow through the cooling stack, high pressure will build and the seals inside the A/C can fail. This can happen when the engine not warmed up, is at idle, and the fan motor is not turning rapidly enough to supply the needed air flow. By tying the controller to the A/C in your coach, it appears the solenoid will activate to increase the speed of the fan motor under those types of conditions.

[Aroadracer]

Originally Posted by Ljwt330

There is logic to the solenoid being wired to the A/C clutch and fan relay. If the A/C is turned on and there is inadequate air flow through the cooling stack, high pressure will build and the seals inside the A/C can fail. This can happen when the engine not warmed up, is at idle, and the fan motor is not turning rapidly enough to supply the needed air flow. By tying the controller to the A/C in your coach, it appears the solenoid will activate to increase the speed of the fan motor under those types of conditions.

Well, maybe my solenoid is not working right. When it is activated (12V applied), the fan speed drops to 190 rpm. I can’t find anything on line about the solenoid. It is a Sauer Sundstrand B5531-10294-12
I may try removing it to see if it can be cleaned and/or serviced.

[Ljwt330]

Originally Posted by Aroadracer

Well, maybe my solenoid is not working right. When it is activated (12V applied), the fan speed drops to 190 rpm. I can’t find anything on line about the solenoid. It is a Sauer Sundstrand B5531-10294-12
I may try removing it to see if it can be cleaned and/or serviced.

Please understand that my explanations are generic and may not apply directly to your coach. My response about the fan speeding up when A/C is turned on is a general statement. The way yours is wired and the operation of the solenoid is likely correct but without a schematic, this is all a guess.

Applying voltage to your solenoid with a resultant drop in fan rpm is consistent with the proper operation of the the control valve. The control valve is normally closed when without power and being closed, pressure is increased in the pilot circuit resulting in more fan speed. When you put 12v to the solenoid, it will open, reducing pressure and lower fan speed. That is just what you did and the fan slowed, as it should.

Don't let me mislead you. I don't have access to the wiring schematic, but from what you describe, the solenoid is working properly when energized and your issue is why is it not being energized at start up and a cold engine?

Is there a charge air temperature sensor shown anywhere on your diagram?

Here's a thought, again, without access to a wiring diagram. Perhaps the A/C and fan relay supply power to the control solenoid when the A/C is OFF. If the relay is a five terminal relay, it may default power to the terminal that is wired to the control solenoid, supplying power that opens the valve and reduces fan speed. When the A/C is turned ON, the relay switches that power to the A/C fan or clutch, de-energizing the control valve solenoid which causes the fan to speed up.

If the above is correct, a faulty relay at the A/C could be stuck in the position which cuts power to the control solenoid, resulting in the failure of that solenoid to open when it should.

[Aroadracer]

Larry, you have been very helpful and I really appreciate it. I now have a good understanding of how the system should work. What I found out today by tracing circuits is my schematics are not correct. It is wired, however, to have the Hyd. fan solenoid energized with the AC off, key on; and switched off with the AC on. This makes sense as no ac = low fan speed when cold (solenoid energized). When the ac is turned on, the solenoid relay breaks the ground to the solenoid and it drops out = high fan speed. Now the remaining problem I have yet to sort is there is no power going to the hyd. fan solenoid. From the schematic, power is supposed to come from the alternator and the same circuit goes to the kill switch relay. However, there is no continuity between these wires. I may have to find an alternate 12V source or run another wire from the kill switch relay to the hyd. fan solenoid. Making progress!

[Aroadracer]

Larry, I re-read your post above and realized that what you proposed was exactly how it is wired to operate. Thanks again for your input!
Jim

[Aroadracer]

Update: I found a contact strip in the engine compartment with unused 12V circuits. Connected the yellow (power) wire going to the fan solenoid and it works! When the engine is cold, the engine fan now runs at 190 rpm. When the OTC AC is turned on, the fan speeds up to 780. The wax valve should speed the fan up as the engine heats up. I still have to verify this.

[Ljwt330]

Originally Posted by Aroadracer

Update: I found a contact strip in the engine compartment with unused 12V circuits. Connected the yellow (power) wire going to the fan solenoid and it works! When the engine is cold, the engine fan now runs at 190 rpm. When the OTC AC is turned on, the fan speeds up to 780. The wax valve should speed the fan up as the engine heats up. I still have to verify this.

Sounds very encouraging!

Question. The fan solenoid to which you connected the wire, is that the solenoid or the relay for the A/C fan? I'm trying to visualize the wiring from your posts.

[Aroadracer]

The 12V power wire went directly to the solenoid valve which is hydraulically in series with the wax valve. The solenoid is switched on and off by a relay which applies a ground leg in the normally closed position. So when the relay is “off”, the ground is connected, the solenoid is activated opening up the oil passage and slowing the fan. The fan relay is energized by power from the ac relay which also engages the ac compressor clutch. When the fan relay is energized, it breaks the ground to the solenoid and it closes. The reduced oil flow with the solenoid closed speeds up the hydraulic fan.

[Ljwt330]

Originally Posted by Aroadracer

The 12V power wire went directly to the solenoid valve which is hydraulically in series with the wax valve. The solenoid is switched on and off by a relay which applies a ground leg in the normally closed position. So when the relay is “off”, the ground is connected, the solenoid is activated opening up the oil passage and slowing the fan. The fan relay is energized by power from the ac relay which also engages the ac compressor clutch. When the fan relay is energized, it breaks the ground to the solenoid and it closes. The reduced oil flow with the solenoid closed speeds up the hydraulic fan.

Thanks, that's how I envisioned it. So the power to the hydraulic control solenoid is now supplied by the yellow wire connected to your new source, and the A/C relay opens the ground connection of the control solenoid, closing off oil flow.

Next question, where was the yellow 12v wire to the control solenoid originally connected?

[Aroadracer]

The schematic showed it coming from the alternator but there was no continuity. So I couldn’t trace the source.

[Old Scout]

Interesting discussion--Larry is right on track--IMHO.....our vintage Alpines have just the mechanical wax valve that links fan speed to engine temp--but no dash A/C interface....later Alpines have an electronic fan controller...our manufacturer recommended installing an after-market solution with a solenoid valve in series with the wax valve, controlled by AC compressor clutch circuit....curious as to whether your solenoid valve is OEM or after-market...knowing that might help you find the source of the problem...curious, assume the dash AC is working and compressor clutch is cycling?