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Old 06-24-2024, 05:06 PM   #1
Mini-Skoolie
 
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Exclamation Hydraulic Fan Drive System

Okay so I am seeking a little info from hopefully some experienced users here in this wonderful community. Our bus uses a Hydraulic Fan Drive System- this system powers our charge air cooler(radiator fan) and also our power steering. We have recently ran into some high temp issues and have diagnosed the problem as a part of this hydraulic system-specifically the thermovalve which is a thermostatically sensitive hydraulic valve. Basically a fancy way of saying it is a coolant thermometer and a valve. It is mounted in the side of a main coolant pipe and has its own hydraulic oil lines in and out. When the coolant rises in temp it restricts oil flow which in return down the line makes the fan speed go faster. This valve which I will attach a picture of is being sold only by bluebird for $1800 cost. Im hoping somebody has some experience with this valve or scenario, maybe knows of some after market options or possibly a way to refurbish the part itself. 1800 would get me a new transmission so thats a hard pill to swallow, just hoping for some sort of work around as we are stuck in Arkansas until we manage this issue.

I have also attached the HFDS section of the service manual.
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File Type: pdf Hydraulic fan drive system manual.pdf (813.0 KB, 10 views)

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Old 06-24-2024, 07:23 PM   #2
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Have you tried to unplug your charge air over-ride solenoid? That should cause your fan to speed up. Another option to get you moving is to install a hydraulic valve in the control line to restrict the pilot flow.
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Old 06-24-2024, 08:22 PM   #3
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My bus also has a hydraulic fan drive. AFAIK, all such drives are broadly similar: usually there's a solenoid (i.e. electrically actuated) hydraulic directional control valve that when energized by 12V from a temperature switch will divert some of the oil flow back to the reservoir, therefore making the fan run at half speed until the coolant reaches a predetermined temperature. Upon reaching that temperature the temperature switch opens, breaking the flow of power, and the DCV defaults back to its normal mode of full-flow so the fan can then run at full speed. If you want to always run your fan at full speed, all you need do is disconnect the wire between the temp switch and DCV. Easy!

If your engine is overheating, check the following:
!) Is the fan running at full speed when needed?
2) If not, is the power steering working OK, or is it hard to turn the wheel? If so, maybe the PS/Hydraulic pump is bad, or the priority control valve is sticking.
3) Is the radiator clear of debris and clean?
4) Is any air leaking through gaps around the sides of the radiator and/or shroud instead of being pulled through the core? Any small gaps are easy to block.
5) Are there cold spots on the radiator, indicating internal blockage(s)?
6) Is there sufficient hydraulic/PS fluid in the reservoir?
7) If you have engine-driven A/C, does switching it on make the fan run at full speed?

A a temporary work-around, just switch on all the heaters and defroster, and this should drop temps by several degrees. My bus's heaters and front defroster have a combined output of 150,000 BTU/hour, so they will drop my temperature by about 4 or 5 degrees.

$1800 for a DCV is absurd. Find out who makes it (Eaton, Vickers, Danfoss, etc), then buy is through a hydraulic supplier, probably for less than half Blue Bird's price. Take the old DCV in to have someone identify its manufacturer and part number. Blue Bird does not make these valves: they just buy them from established makers. If it's still OK, it's prudent to buy a spare and keep it "just in case"; I did that when my old Danfoss valve died, and I bought the last three NOS valves in the country for dirt cheap!

If/when you get it fixed, consider installing two hydraulic pressure gauges, one to show the high pressure (1500-ish PSI) going to the fan motor, and one to show the return pressure back to the reservoir (much less than 100 PSI). They will make trouble-shooting much easier.

Good luck, John
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Old 06-24-2024, 09:31 PM   #4
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So unplugging the charge air override solenoid (COAT) the fan currently does not run full speed but it will go full speed if you increase the rpms. According to the testing procedures this is telling me the thermovalve is the problem in the system. We have discussed the option of installing a bypass around the thermovalve if necessary in the temporary till we can get to our destination. The thing I wonder about that is getting the right pressure. The pressure set by that valve is dictating the minimum and maximum fan speed correct? The service manual seems to state that the charge air solenoid will take the fan to a moderate setting only.

What would be the process for checking and/or removing the diverter valve on the pump?

I feel a bit better knowing Bluebird does not make that part. Im gonna take it off tomorrow and check in with some regional hydraulic shops.

Edit- I should add; the coolant system has been completely taken care of, new water pump and thermostat and its been flushed but we are gonna blast it out while we’re doing this current work. Also there is no cabin a/c or heat that runs on this system.
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Old 06-24-2024, 10:14 PM   #5
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Youtube feed had this when I logged on tonight. It has a part 2 which has an additional info and he refers to it as a wax valve.


I found this earlier today

https://www.irv2.com/forums/f115/fan...en-376611.html

This looks similar
https://coachparts.net/blue-bird-wan...vethermostatic
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Old 06-25-2024, 09:34 AM   #6
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Quote:
Originally Posted by BamaBus View Post
Youtube feed had this when I logged on tonight. It has a part 2 which has an additional info and he refers to it as a wax valve.


I found this earlier today

https://www.irv2.com/forums/f115/fan...en-376611.html

This looks similar
https://coachparts.net/blue-bird-wan...vethermostatic

Wow thank you, this is a lot of useful information. Ive read through so many pages of this already! Now I find myself wondering when everybody is replacing these wax valves how do they make sure they dont leave air in the system??
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Old 06-25-2024, 09:58 AM   #7
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When you read pages 5 and 6 of your manual it explains how this works. Disconnecting the charge air solenoid gives you medium speed fan. Restricting the thermo valve circuit increases the fan speed until you reach maximum speed. Yours is a modulated fan speed system. Some are on-off. Either way adding a hydraulic needle valve in the thermo valve hydraulic line you should be able to up-regulate your fan to full speed and move on to home base and then fix it. If you can't find the thermo valve at a reasonable price you can make a system that will do the same thing.
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Old 06-25-2024, 09:58 AM   #8
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Whatever you do, DO NOT tamper with or change the pressure setting of the valve itself. If you change its pressure setting there's a very real probability that the fan motor will burst due to a pressure spike. After I completely rebuilt my entire cooling system (new radiator, new fan, new fan motor, new hyd/PS pump, new t'stats, etc etc) a few years ago, I also installed a Prince RD-1875H pressure relief valve to absolutely prevent any pressure over 1500 PSI, even brief spikes, from reaching the fan motor. So far, so good.

John
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Old 06-25-2024, 03:15 PM   #9
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interesting issue, glad it's not my issue !

I found this "conversion" kit.
not sure if it will work for you but hey, it's free info for now...


https://sourcerv.com/conversion
Quote:
If you have a coach with the Sourer-Danfoss hydraulic fan drive and have experienced failures related to the electronic control unit known as the "FDCA" we have an economical answer to the problem. When these controllers fail, the fan typically will go to full speed and will not modulate; creating several undesired effects.

The pilot valve (wax valve) system in this kit is time tested, extremely reliable, and more efficient than the electronic FCDA.
Installation instructions

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Old 06-25-2024, 05:38 PM   #10
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Okay so we went to the local hydraulic shop and built up an inline work around with a valve and a pressure gauge on it. Installed it and boom! Looks like we were wrong, well right in a way because the thermovalve is not working but thats because the whole pilot circuit doesnt seem to have any pressure. The guage is not registering anything.

Now this is where I need to step back and regroup, there was oil in the lines so Im guessing theres not a blockage. My first thought is the valve in the back of the fan motor? I only say that because Im thinking the hydraulic pump and priority flow divider are okay only bc the fan speed will increase with the rpm but only when the solenoid is de-energized. In my head that shows me that the pump is in fact pushing hydraulic oil and the flow divider is sending it to the fan motor.

Im thinking the problem is in the fan motor and its control valves but I would love if somebody could walk me through this a little. Ive read this service manual so many times Im seeing it in my sleep but it still doesn’t fully make sense to me.

Is the pilot circuit always under pressure? Or is it an only while driving situation?
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Old 06-25-2024, 09:56 PM   #11
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Okay okay sorry for the double post but I keep coming back to this question and I cant figure it out.

Why does the fan increase with the engine rpms ONLY when the solenoid is de-energized?
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Old 06-26-2024, 08:23 AM   #12
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Remember the hydraulic system is biased to your power steering with some type of priority valve. That is a safety thing. If you have low pressure or flow the fan motor will be starved. But you wont know until you pressure test it.
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Old 06-26-2024, 08:48 AM   #13
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Quote:
Originally Posted by s2mikon View Post
Remember the hydraulic system is biased to your power steering with some type of priority valve. That is a safety thing. If you have low pressure or flow the fan motor will be starved. But you wont know until you pressure test it.
Is there any chance you know what sort of pressure I should be looking for. If I test the line coming off the diverted how many psi should be on it? Is there a range for each component or is it a consistent psi throughout the whole system? Also do I need the hydraulic fittings for each size line or could I get away with something from the hardware store? The hydraulic place was a decent drive away and took most of the day yesterday, if I could use an alternative that would be more helpful
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Old 06-26-2024, 09:23 AM   #14
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If you look at the last page of your manual it gives fan rpms and pump pressures. If you have a hand held tachometer (I highly recommend having one) you could test fan speed and be accurate and compare your data to the manual. A pressure gauge on the system should show as per the manual is 1994 psi. So that is your pressure relief setting. It also states that it has to be at 205 degrees to test fan speed. So if the thermo / wax valve is not working I don't think you can test it. The thermo valve is designed to as as a restriction to the pilot circuit to effect higher pressure to the fan motor. The charge air solenoid bypass allows the fan to run at 50-60% so 1100 to 1300 rpm. There is a test point. You will have to bring the engine rpms to about 2200. These hydraulic fan systems are also used on water well drilling rigs too. They work very well until they don't.
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Old 06-26-2024, 09:31 AM   #15
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[QUOTE=Mollymolasses;511546]
My first thought is the valve in the back of the fan motor? I only say that because Im thinking the hydraulic pump and priority flow divider are okay only bc the fan speed will increase with the rpm but only when the solenoid is de-energized.
[quote]

The way I read it....

When the charge air temperature reaches 150° Fahrenheit, the charge air override sensor will open, de-energizing the solenoid valve. The closed valve will make a restriction, increasing pressure in the pilot operated circuit. The pressure increase will force the bypass valve toward the closed position, increasing the fan speed.

Quote:
Originally Posted by Mollymolasses View Post
Is the pilot circuit always under pressure? Or is it an only while driving situation?
Only under pressure when the engine is running....If the "Pump" don't spin then there is no pressure to be had.

Pressure will continue to increase in the pilot circuit, until the relief valve setting is reached. The valve will open, maintaining a moderate pressure against the bypass valve, while maintaining a moderate fan speed.

You have 2 components that are in-line (series) with each other and both are temperature dependent.
The air charge open up at 150 degrees and the thermo valve will begin to operate around 190 degrees. the thermo valve will adjust the flow/restriction based on coolant temp,


The thermo-valve is a thermostatically sensitive hydraulic valve that monitors
engine coolant temperature. This is the second valve in the pilot operated circuit.


You were right in saying this "Basically a fancy way of saying it is a coolant thermometer and a valve."

I really don't see an easy way to bypass this other than by either using a toggle/button to manually operate a valve in it's place (no thermal but straight electrical).

You could go fancy and build a new vale circuit if you can find a thermal sensor at the correct temp ranges, attach a relay and electrical valve replacing that system altogether with something you can repair later with more available parts.

I would test your air charge sensor for correct operation, hot water, laser temp reader. test the sensor cold for restriction then heat up to 150 and see if it opens.

try to do the same for the thermovalve and see if it swings open and closed based on temp.
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Old 06-26-2024, 09:45 AM   #16
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The older systems had a Kysor thermoswitch that was set at 210 on 205 off. That could operate a electric over hydraulic valve through a relay with a wire going to the drivers panel to have a fan over ride function.
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Old 06-26-2024, 02:46 PM   #17
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Only $360 bucks !

https://www.nwrvsupply.com/product/s...3-1-09857-200/

553/1/09857/190
553/1/09857/190 THERMO

HYDRAULIC VALVE






EBAY-> $120 bucks
https://www.ebay.com/itm/275932586645
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Old 06-26-2024, 05:36 PM   #18
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Quote:
Originally Posted by ewo1 View Post
Buy both of them right now! You should always keep a spare of critical-but-hard-to-find small items. That's why I now have two spares of my even-more-unobtainable Danfoss 7WA110-2 valves.

John
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Old 06-26-2024, 06:34 PM   #19
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Seems that there are multiple part numbers possibly referring to different operating temps. The pdf gives an operating range of 185° to 200°, but that may not be correct since no specific vehicle was mentioned, that I saw. Hopefully there is a temp on the valve itself, if that is what is needed.
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Old 06-28-2024, 07:52 PM   #20
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Okay everyone, thank you for all the helpful responses. So this is where we’re at. We replaced the fan motor bc it seemed to be leaking badly and on the test drive afterward it seemed to be doing better, regulating itself at between 200 and 220 which for a cummins Im told is ideal operating temp. Now once we finally did a few good pushes up some hills in this lovely 90-100 degree weather it seemed to finally push that 220 threshold. Took it immediately back into the park. The in line valve we installed to bypass the thermovalve still wasnt registering ANY pressure so Im thinking we maybe didnt build that bit right. Took it out and attached the lines back to the ‘presumed busted’ thermovalve bc unfortunately anything Im finding isnt matching part numbers for me so we were trying the temporary bypass. But we reconnected in hopes of better diagnosing the system failure. Now, currently after the fan motor replacement the fan speed will increase at all times with the revving of the engine. However when I unplug the charge air override sensor the fan does not go any faster? I assumed from everything Ive read that the solenoid can only fail in ‘fan full speed’ position. Is it possible for it to have failed in the opposite direction? And if not what do you all think is going on?


Also I am rechecking the in line valve to make sure I put it together correctly. I will attach a picture. Please feel free to take a look and tell me if I reversed the pieces or anything really.

The original Bluebird part number for the thermovalve is - quoted from a Bluebird email-
“ 01964964 - THERMOVALVE,HYDRAULIC,CUMMINS ISB – $1562.05 Each 5 available at bluebird”
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