LMTV radiator fan stuck

[derpschitz]

My LMTV radiator fan is stuck in the "engaged" setting, not sure where to begin troubleshooting so hopefully I can get started with a few questions for those who know these things better than I do. I'm guessing one of two things-- either the clutch is stuck or there is something borked electrically. It worked fine last time I drove. The switch to disable the fan does not appear to have any effect (light comes on but no difference, fan remains loud and spinny).

1: is the default state of the radiator fan "engaged" and it gets disengaged when the system is working properly, until it needs to kick in?
2: what breaker or relay is responsible for this circuit?
3: is it possible to short connectors in the electrical panel to test whether or not the clutch is stuck?

Thanks!

 

[Suprman]

See if the solenoid is stuck and and if its working properly then manually send a squirt of 150psi air to the clutch theres a fitting over the shroud.

 

[coachgeo]

first step.... search and read discussions on the fan.... plethora of discussions on them and their clutch.
second step.... get and fiddle thru the TM's (or is that first?) They can be found via the first page of Steel Soldiers. Very first forum.

yes as a protective measure the fan defaults to engage.
air solenoid is found inside the passenger kick panel; under the fuse box, technically called the PDP (power distribution panel)

 

[Awesomeness]

The default state of the fan is engaged. When the coolant switch is below the temp (215°?), it closes the circuit, engages the air solenoid, and air disengages the fan clutch.

There is more info about it in the Common Issues & Fixes document, here in my signature links...

 

[Ronmar]

What truck is this on?
On an A0 CB22 sends 24v thru a 205F normally closed sw to power the solenoid. The solenoid provides air to release the clutch. When the temp goes over 205, the switch opens, solenoid releases the air and the fan engages. The fording sw bypasses the temp sw to feed power from cb22 directly to the solenoid.

If this is an A0. Since the sw also doesnt work, i would start with CB22. You can power the solenoid under passenger dash directly with 24v to test it.

On an A1 the ECU provides power to the solenoid to disengage. CB22 provides the fording sw power, so if neither disengages the fan I would problaly start at the solenoid...

 

[NDT]

FMTV Fan Clutch Repair | SteelSoldiers

Issue I had long ago.

 

[derpschitz]

What truck is this on?
On an A0 CB22 sends 24v thru a 205F normally closed sw to power the solenoid. The solenoid provides air to release the clutch. When the temp goes over 205, the switch opens, solenoid releases the air and the fan engages. The fording sw bypasses the temp sw to feed power from cb22 directly to the solenoid.

If this is an A0. Since the sw also doesnt work, i would start with CB22. You can power the solenoid under passenger dash directly with 24v to test it.

On an A1 the ECU provides power to the solenoid to disengage. CB22 provides the fording sw power, so if neither disengages the fan I would problaly start at the solenoid...

1998 M1078A1. I've checked CB22 and it's fine. Checked the sender with a boil test and it works properly. The fording switch does not disengage the fan. I also tried shorting/unshorting the sender cable and it makes no difference. So either it's the solenoid failing, or the clutch is stuck. Will need more daylight to do more testing.

 

[Suprman]

Generally a 98 is a first gen truck. Fan clutch gets stuck from sitting. Air connection over shroud disconnect and use a compressor to give clutch a blast of 140 psi air see if it frees up

 

[Ronmar]

Well if there is more than 85 PSI in the tanks. You should hear the solenoid send air to release the fan clutch when it is energized, and it should cutoff supply and vent the line to the clutch, releasing the air and engaging the clutch. You can also disconnect the airline right on top of the fan shroud and apply air there, which should release the fan clutch and allow you to spin the fan by hand…

sounds like you might have an A0.5 if you have a thermal fan switch on the upper radiator pipe. The full A1 uses the engine coolant temp sensor and a programmed temp setting in its ECU to control the power to the fan solenoid…

 

[derpschitz]

Couldn't leave it alone so I did some more troubleshooting. I think it's the solenoid. Plenty of pressure supplied on the manifold side, but none coming through the pipe to the fan clutch after starting up and letting it run for a while. Photos forthcoming...

 

[derpschitz]

So, this guy here I assume is the line going to the fan. I disconnected it as shown to see if it would push air after start. Engine cold, idled until brakes, CTIS, etc were well pressurized and the air dryer was honking periodically. Nothing happened here at the solenoid. I tried the fording switch, nothing. Knowing that CB22 is fine, the sender is fine, even if the clutch was stuck I should still get air pushing through from this nozzle, right? When I disconnected the other air line to remove the solenoid it about blew me out of the cab so I know it has air.

 

[derpschitz]

I guess at this point the next thing I can test is "what is happening on the solenoid wires?" so what should I look for here? Assuming 24v power? What is the default vs activated state (ie: does power to the solenoid open or shut the valve?)

 

[GeneralDisorder]

Check for 24v/ground at the solenoid connector. When the solenoid is de-energized it does not send air to the fan clutch - the line to the fan clutch is vented on the solenoid's vent port. It has to receive power to send air to the clutch and disengage the fan. So you may still have an electrical issue or the solenoid could have failed electrically and is just dead and unable to disengage the fan clutch.

 

[derpschitz]

I opened up the solenoid, looks like there was a bit of schmutz on the contact part of the valve. Maybe this is what was making it stick? The rest appears OK at least to me. I might have a 24v power supply around here somewhere I can test it with.

 

[GeneralDisorder]

These solenoids are known for having weak coils and being unable to actuate properly. I would replace it after checking for power at full operating pressure, etc.

 

[flyfishtrailer]

If you end up needing a new fan clutch switch, one of our SS members sells them on e--y (callmecolt)

 

[TomTime]

If you need the fan solenoid you order them directly from the distributor.
Ronmar and Callmecolt both have good videos and both, I believe, give you the part numbers for the parts you need.

 

[derpschitz]

If you end up needing a new fan clutch switch, one of our SS members sells them on e--y (callmecolt)

I ordered one from him, good thing anyways because this old one won't work despite being cleaned up, and I broke off one of the brass fittings reinstalling it.

I get 27v from the plug on startup and with the fording switch on. Is there a way to get it to "engage" thinking that the thermal sender has been tripped? Can I unplug the sender to simulate this?

 

[Ronmar]

Yep, unplug the sender or selenoid. To remove fan air and engage the clutch, that is of course with a working solenoid...

 

[derpschitz]

Yep, unplug the sender or selenoid. To remove fan air and engage the clutch, that is of course with a working solenoid...

I gotta make sure the electric stuff is functioning properly first, otherwise the solenoid won't matter.