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Topic: '94 U280 Hydraulic Fans (Read 510 times) previous topic - next topic

'94 U280 Hydraulic Fans

8.3C experts: Dual hydraulic fans should default to high speed with bypass solenoid disconnected. Mine do not change speed. It ran hot at 215 on a trip. I replaced the solenoid and the valve cartridge. No change in speed. Any ideas?

1994 U280, Build 4490
Deming, NM.

Re: '94 U280 Hydraulic Fans

Reply #1 –
Fluid level?
Condition of fluid and filters?
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: '94 U280 Hydraulic Fans

Reply #2 –
Quote from: wolfe10 –
Fluid level?
Condition of fluid and filters?
Not a cooling issue. It's a fan (hydraulic) issue. They should default to HIGH speed with or without coolant. Mine do not. They do run on low speed.
1994 U280, Build 4490
Deming, NM.

Re: '94 U280 Hydraulic Fans

Reply #3 –
There is a pressure regulator in the system that is used to control the maximum fan rpm. This is not the solenoid valve. This could be bypassing back to tank. Also motors have a case drain line, the small ones. Motors can bypass back to tank. The pump can also be at fault. Foretravel didn't install any pressure taps for testing.
  Do you have a copy of the hydraulic diagram?
1994 U280
Build #4451
"If everyone is thinking alike, then somebody isn't thinking"

Re: '94 U280 Hydraulic Fans

Reply #4 –
Quote from: Hammer2100 –
There is a pressure regulator in the system that is used to control the maximum fan rpm. This is not the solenoid valve. This could be bypassing back to tank. Also motors have a case drain line, the small ones. Motors can bypass back to tank. The pump can also be at fault. Foretravel didn't install any pressure taps for testing.
  Do you have a copy of the hydraulic diagram?
Well. Where is the pressure regulator located? I've not heard of this. In the past, I have disconnected the solenoid and the fans ran on high speed. There is no variable speed control. It's either low or high. What motor? Since the fans run on low speed, I assume the pump is good. I do not have a diagram. Thanks for your help.
1994 U280, Build 4490
Deming, NM.

Re: '94 U280 Hydraulic Fans

Reply #5 –
Twig,
  Sorry I work on heavy equipment. Fans are hydraulic motors.
I have a diagram and will try to post it for you. I will also take a picture of the regulator on ours. Build 4451 hopefully the same.
I think this has been brought up before.
1994 U280
Build #4451
"If everyone is thinking alike, then somebody isn't thinking"

Re: '94 U280 Hydraulic Fans

Reply #7 –
Quote from: Ralph –
Said another way:
HYDRAULIC fluid level?
Condition of HYDRAULIC fluid and HYDRAULIC filters?
Done FIRST.
1994 U280, Build 4490
Deming, NM.

Re: '94 U280 Hydraulic Fans

Reply #8 –
Twig,
    Here is a picture of the relief valve, which is on the bottom of the tank. A #8 hose goes to it. This could have stuck open.
  Also the system diagram of ours. I'm getting ready for a trip and I think I'm going to check my fan speed tomorrow.  ^.^d
1994 U280
Build #4451
"If everyone is thinking alike, then somebody isn't thinking"

Re: '94 U280 Hydraulic Fans

Reply #9 –
Interesting. Great help. I've reworked under the sump already and don't remember that fitting but I'll look tomorrow. If it's there, of course my next question would be.........now what?
1994 U280, Build 4490
Deming, NM.

Re: '94 U280 Hydraulic Fans

Reply #10 –
IF (yes, a large IF) the relief valve serves the same purpose as on the "upgraded" fan control Foretravel engineers designed when the cooling hydraulics on our 1993 U240 failed it is very easy to adjust PSI.

On the right side of the picture you will see it mounted on the frame rail.  On our setup, it was easy to adjust (lock nut and screw) and take hydraulic PSI from zero to over 2000 PSI.

So, if PSI at cruising RPM with fan bypass set for high is below spec, adjust it.  You will see the pressure gauge immediately "upstream" of the relief valve. This redesigned system had no hi/low-- much simpler, but did run the fan unnecessarily high when not needed.  My solution was to set the PSI lower in winter, higher in summer with the adjustment taking less than 2 minutes.

Certainly worth investigating.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: '94 U280 Hydraulic Fans

Reply #11 –
Twig,
    I checked my fan speed at low idle today. Fans are 650 RPM and with solenoid unhooked they go to 900 RPM. I didn't see what they were at high idle as I by myself. I used a cheap photo tach from Amazon. It's gonna go in the toolbox on the joey.
1994 U280
Build #4451
"If everyone is thinking alike, then somebody isn't thinking"

Re: '94 U280 Hydraulic Fans

Reply #12 –
Quote from: Hammer2100 –
Twig,
    I checked my fan speed at low idle today. Fans are 650 RPM and with solenoid unhooked they go to 900 RPM. I didn't see what they were at high idle as I by myself. I used a cheap photo tach from Amazon. It's gonna go in the toolbox on the joey.

High idle can be set with your cruise control when by yourself. I found the pressure regulator so how do I test to see if it's the problem or not?
1994 U280, Build 4490
Deming, NM.

Re: '94 U280 Hydraulic Fans

Reply #13 –
I've been thinking about that already. I think the easiest, maybe the best is to install a jic tee in the #10 line that goes to the solenoid from the pump. That so you can watch the pressure change. I'm thinking of adding one to ours. I may have a tee at work or the hydraulic shop nextdoor will. I'll try to post a picture.
1994 U280
Build #4451
"If everyone is thinking alike, then somebody isn't thinking"

Re: '94 U280 Hydraulic Fans

Reply #14 –
Quote from: Hammer2100 –
I've been thinking about that already. I think the easiest, maybe the best is to install a jic tee in the #10 line that goes to the solenoid from the pump. That so you can watch the pressure change. I'm thinking of adding one to ours. I may have a tee at work or the hydraulic shop nextdoor will. I'll try to post a picture.

Said another way, since the regulator has not gone out of adjustment I'm thinking that if it's the problem the most logical conclusion would be that it is stuck because it controls HIGH speed and replacement would be the answer (after a hammer adjustment is tried). Since it is......you know.......old, how would one find a replacement? So far, I think you're a genius.
1994 U280, Build 4490
Deming, NM.
 

Re: '94 U280 Hydraulic Fans

Reply #15 –
Twig,
    Here my idea. Part # are hydraulic industrial, most any hydraulic shop or even NAPA can cross them. Even online.
Jic tee 60473-1010
Adapter 60420-1004
Jic to fnp 6506-0604
Cap 60401-0010
A oil filled 3000psi gauge
This should be about 1 coach buck.
    I didn't have time to test this out but I plan on installing the tee soon. We are going on a trip next week. I wouldn't leave the gauge on driving, that's why I showed the cap. I've been thinking about have this installed for a long trip next year, guess it's fortuitous  :o
1994 U280
Build #4451
"If everyone is thinking alike, then somebody isn't thinking"