Good morning Having a problem and at a loss on my 1989 m998 I’ve been trouble shooting a problem with my fan always engaged and have got to a point where the psi going to the fan is 30 and the psi from the rack is only 35? the power steering works great Any ideas Thanks
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Fan clutch low psi, not disengaging
- Thread starter Stevev
- Start date
Still Having a problem and at a loss on my 1989 m998 I’ve been trouble shooting a problem with my fan always engaged and have got to a point where the psi going to the fan is 35 and the psi from the rack is only 35? the power steering works great
Any ideas?
Thanks
Any ideas?
Thanks
- 2,102
- 30
- 38
- Location
- Delta Junction, Alaska
There are several answers, not to mention download the manual & read. Next is take it to a commercial truck shop. OTH trucks use one of several methods to control the fans/shutters. The military didn't invent something new here & probably most of the parts are some version of the civi parts. Often, air pressure holds the fan "Off" (disengaged) & the shutters "Closed". Springs hold the fan engaged & the shutters open - in default position. Then there are temperature/electric controlled switches or valves controlling the air. Keep in mind that the switches & valves may be nominally open or closed. Its best to have the Truck up to normal temperature, after you note the fan & shutters position before truck is started & still cold, but that's my preference. Main tools are grounding test light & ac/dc Fluke Clamp Meter.
I want to say, Good Luck, & its not in Jest. Its really pretty simply, but its best to understand how things work first.
I want to say, Good Luck, & its not in Jest. Its really pretty simply, but its best to understand how things work first.
- 585
- 585
- 93
- Location
- Evansville, IN
cadilac ?
Wire Fox
Well-known member
- 1,252
- 161
- 63
- Location
- Indianapolis, Indiana
The fail-safe/default operation mode of this fan is always on. If there's an electrical failure, the fan will run. If there's a hydraulic failure, the fan will run. If there's a clutch or valve failure, the fan will run. One question to answer that will greatly help us to help you:
Has the fan operated correctly before and has suddenly failed, or is this a new-to-you truck that you're going through and fixing problems as you find them?
If it's either new to you OR has sat for a long time, one thing to consider is if the fan clutch is simply stuck. They often seize in the engaged position while sitting around and it can be tricky to free them. What I did on my unit was get an air compressor up to about 90 PSI with a rubber-tipped blowgun attachment. I disconnected the hydraulic line that feeds into the fan clutch, then pressed the nozzle into the fitting. Then, I just would shoot bursts of high pressure air into the fan clutch for about 3 seconds on, 1 second off. The cycling of the high pressure eventually broke the seized clutch free and I could watch the fan clearly pop in and out of engagement position (you can see it move about an inch forward and back). Once freely moving, I reconnected everything, bled the power steering system, and then test-ran the truck and found everything worked fine.
If that doesn't cut it or doesn't fit your scenario, just remember those basic principles. You've tested pressure. You can still test the time delay module (TDM), the cadillac solenoid valve, and lastly the voltage coming to the TDM. Still no good? Check that all hoses are routed correctly. If all that still fails, get on the market for a new fan clutch.
I believe that the TM details all of the troubleshooting I just mentioned, save for using compressed air to free the stuck clutch (but actually, that might be in there, too...). Using those troubleshooting guides is really awesome and useful to take the lead on all your repairs.
Has the fan operated correctly before and has suddenly failed, or is this a new-to-you truck that you're going through and fixing problems as you find them?
If it's either new to you OR has sat for a long time, one thing to consider is if the fan clutch is simply stuck. They often seize in the engaged position while sitting around and it can be tricky to free them. What I did on my unit was get an air compressor up to about 90 PSI with a rubber-tipped blowgun attachment. I disconnected the hydraulic line that feeds into the fan clutch, then pressed the nozzle into the fitting. Then, I just would shoot bursts of high pressure air into the fan clutch for about 3 seconds on, 1 second off. The cycling of the high pressure eventually broke the seized clutch free and I could watch the fan clearly pop in and out of engagement position (you can see it move about an inch forward and back). Once freely moving, I reconnected everything, bled the power steering system, and then test-ran the truck and found everything worked fine.
If that doesn't cut it or doesn't fit your scenario, just remember those basic principles. You've tested pressure. You can still test the time delay module (TDM), the cadillac solenoid valve, and lastly the voltage coming to the TDM. Still no good? Check that all hoses are routed correctly. If all that still fails, get on the market for a new fan clutch.
I believe that the TM details all of the troubleshooting I just mentioned, save for using compressed air to free the stuck clutch (but actually, that might be in there, too...). Using those troubleshooting guides is really awesome and useful to take the lead on all your repairs.
Thank you so much for such a detailed response
I’m at the point with diagnostics that if I pinch the return like I get 90+ psi and it works perfect
Even tho the Cadillac valve ohms out o think it’s mechanical bad so I ordered one
I have 27v going to it from the tdm box so I hope a new one does the trick
She is new to me
I love do this thing
Just working out all the little issues
Thanks again bud
Really appreciate the help