Hydraulic fluid heat exchanger fans

Hydraulic fluid heat exchanger fans - Printable Version

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+--- Thread: Hydraulic fluid heat exchanger fans (/showthread.php?tid=5067)

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RE: Hydraulic fluid heat exchanger fans - mycbarnes - 07-11-2019

Attached is a picture of the heat exchanger fan relay on my coach as promised. The Bosch relay is in rear engine compartment cabinet drivers side. Bosch 75 amp relay is the black unit bottom center of picture. To the right is a small circuit breaker can that auto resets. On the relay, power from the 12v buss is the red wire via the breaker. Green wire goes to the 12v heat exchanger fans. Orange wire on relay is the 12v positive control lead for relay coil. Black wire is ground for relay coil. The control circuit for the this relay goes up to the remote starter switch. I have not ringed out this part of the circuit yet. So the answer is that on my coach, the fans are supposed to come on when ignition is on. newer coaches move to a thermostat circuit. Which saves wear and tear on 12v fans and power hog. Having no dash hydraulic fluid temperature gauge in a coach to indicate that this early type circuit of 12v heat exchanger fans system is not working properly makes me suggest to all that it's something to make sure is working properly. The fans when on are pretty easy to hear, key on, engine not started yet.

RE: Hydraulic fluid heat exchanger fans - RegaNewell - 01-05-2022

Well I was told when I bought my Coach from an Individual, that the heat exchanger was for extra transmission cooling. I was also shown were the switch was located to turn it on and only needed it when pulling a heavy trailer. So for the last 10 years, until I read this thread this morning, this is what I thought to be true. I had to pull this unit out a couple days ago to get to an air leak above it. I lowered the unit, and broke the fitting loose and out came red fluid, that I just assumed was transmission fluid. I assumed since the transmission was lower then this line that it would suck air and not siphon out all the fluid from the transmission. So I walked away and let it drip. About 30 minutes later, Pam hollered and told me to look under the coach. I immediately started crying and was hollering for the kitty litter. Everyone that knows me understands, that I am still trying to realize the world still turns, even when you stain your concrete. After putting down 200 pounds of oil-dry, I got back underneath and tightened both lines back up. Then I thought the best thing to do, since I was completely soaked in fluid was to work as fast as I could and get both lines unhooked and pushed up to the Coach floor (higher then the transmission). I now had fluid running down both arms, chest and face, after about 5 minutes the fluid stopped flowing. I am so happy that I stumbled upon this thread. I now know that this is not a transmission cooler and that my hydraulic tank is now completely empty. The only time I have heard these fans on the unit come on, is when I manually turn them on with a switch mounted in the very top left corner of the wiring bay inside the engine compartment. I now realize that I am going to have to completely understand how this system is supposed to work, and why mine has to be manually switched on. I am including pictures of the mess, the unit and wiring relays. What type/weight fluid is used in this unit? I also have a non-labeled switch mounted on my dash, next to the HWH unit. I was told this was used to switch the main hydraulic fan in low or high. It also looks like I will have to learn how to attach pictures correctly and in the right order.

RE: Hydraulic fluid heat exchanger fans - Richard - 01-05-2022

I don’t know if this will help you figure any thing out. The 95 I owned, Coach 390, was like Terrie Barnes. Those hydraulic cooling fans came on when the ignition was turned on.

On the 99, Coach 512, they do not come on when the ignition is on. I assume they are thermostatically controlled since I have never overheated the hyd fluid.

The point is, some of those extra switches you have may have been added to customize the operation of the engine cooling fan, and the hydraulic cooling fan.

And I hate taking baths in ATF or coolant.

RE: Hydraulic fluid heat exchanger fans - RegaNewell - 01-05-2022

Richard,

It was a big mess!! Everything I touch starts out small, and ends huge! Does this system take an 80W,90 Gear Lubricant?

Jeff

RE: Hydraulic fluid heat exchanger fans - bestgenman - 01-05-2022

Oh my gosh NO heavy oils! Mine uses synthetic transmission fluid with a classification that escapes me just now. Contact Newell, ask Mike or Cresslie. Maybe other Guru’s know.

RE: Hydraulic fluid heat exchanger fans - House Divided - 01-05-2022

Jeff,

Your fan control system appears to be the same as mine - at least your pictures show all the same hardware. Fan theory is pretty straight forward - the fans will have power available with ignition on, but will only energize if the thermal switch (the largest round black sensor closest to the engine in the back of the reservoir- 4th picture) reaches 160 degrees or so
and closes the control circuit to the large relay in the rear compartment, sending power to the fans.

My thermal switch failed, and since draining the tank didn't sound like fun at the time, I simply bypassed the failed switch allowing the fans to be controlled by the ignition until I could do a proper repair. I would guess maybe your extra switch is a work around for a failed thermal switch.

As far as fluid, I refilled my system with what the original owner used for many years- Napa 75206 ATF 4. Which is a synthetic transmission fluid - I believe a Chrysler specification.

RE: Hydraulic fluid heat exchanger fans - Richard - 01-05-2022

ATF

RE: Hydraulic fluid heat exchanger fans - RegaNewell - 01-06-2022

Thank you all for the information. I thought it smelled and had the same skin moisturizing effect as ATF, lol! I am going to run through the electrical system now and get it operational as designed. Does anyone else have the switch mounted in the dash for two speed operation on the main cooling fan? The location and installation of my switch looks like an after thought from someone in the past. I always run it in high speed, not sure when I would switch it to low speed unless we were driving in very cold areas. Maybe the system is supposed to run in low speed until it reaches a certain temperature, and automatically switch to high speed?

RE: Hydraulic fluid heat exchanger fans - Richard - 01-06-2022

Yes the main fan is controlled by the DDEC. On the lower left side of your engine, you should see a gold colored manifold with hoses going to the fan motor. The solenoid on that manifold is what changes the speed. When the solenoid fails, the default is to high speed.

By running at high speed all the time, you are giving up about .5 mpg.

RE: Hydraulic fluid heat exchanger fans - RegaNewell - 01-10-2022

Still trying to get my main Hydraulic fan working correctly. Richard, The solenoid for the main fan is working. you are correct the valve fails to high speed. When I apply 12 volts to the solenoid, the fan slows to low speed. I have found that the switch on my dash does nothing. It does not change (apply or remove voltage) to this solenoid. Right now I do not have 12 volts present, I will have to trace it back and see what all is involved in this circuit. David, our coaches are step sisters, I'm sure they were both on the floor at the same time. I was wondering if you have an extra breaker that is not labeled below the Hydraulic #2 cooling fan breaker. The installation looks factory but there is no label. I found this breaker to be bad, there is no information on it anywhere. It gets it's power from the bus bar that feeds the first 3 breakers. It feeds a purple wire that I have not tried to trace out yet. My book has all the information on every electrical, fuse, and breaker panel except this compartment. Richard, does this signal come directly from the DDEC? I do believe that we had to replace the DDEC a few years back. Maybe I need to have it looked at and make sure this fan circuit is actually programmed. I really think we used to get better mileage too, 6.8 to 7.0mpg. Now we average 6.3 to 6.4mpg. I may owe Pam an apology, I thought the drop in mpg was due to her right foot.

Jeff