RPM engages clutch fan?

[Andyrv6av8r]

Its in the valley of the engine near the injection pump and throttle cable area. It has a little white plastic wheel that is part of the switch.

What about the four speed engines? I don't have that on mine?

 

[fpchief]

Little switch on IP pump is two fold. On the 3 speed transmissions (I don't have experience with 4 speed rigs) it controls the kick-down solenoid AND triggers the TDM to DISengage the fan to go for a swim.

Should give you about 20 seconds to get wet before comes fan back on.... IF the engine is above 190 ish ++ and fan temperature switch (in water crossover) is working properly.

(Note) fan temp switch is an OPEN switch when 220 ish hot or fan is running. Closes at 190 ish and below so fan should be off. This is the only switch that cycles fan on and off while happily going down the road.

OR

The kick-down switch (side of IP) triggers (momentary 24 volt pulse) to start the TDM to begin the 20 second +/- swim feature applying power to the Cadillac valve which disengages fan even if the engine is hot, overriding the temp switch. Confusing as heck, but it works.

To pass grand-ma, the kick-down switch needs to be fully engaged, peddle to the metal to HOLD the solenoid engaged on the valve body in the transmission. Added bonus TDM get the trigger pulse too and off you go with a little more HP. All things working properly of course.

Those kick-down switches do go bad or could be out of adjustment. Pull one of the wires to it to check if fan STILL follows throttle position.

Does the transmission down shift correctly at peddle to the metal?

Question for you. Have you been reading the little book? >https://hummerhuren.files.wordpress.com/2013/01/hmmwv_test-diagnostics.pdf

Taking a survey to better serve, CAMO

An after thought... saw a picture posted a couple weeks back with a new fan temp switch that looked like a knockoff. SS was having fan issues. Just wondering here. You can set you clock by the humv posts. FAN problems in the summer. Start boxes in the winter.

Just like they taught us in driving school....floor the accelerator prior to entering deep water. It will stop the fan. But that was in the 3 Spds.

 

[AAVP7]

What about the four speed engines? I don't have that on mine?

In the 4-speed trucks, the time delay switch is relocated to the rear of the engine valley. As far as I heard, it no longer activates transmission kickdown, that is done by the TCM in conjunction with the throttle position sensor.

 

[Retiredwarhorses]

In the 4-speed trucks, the time delay switch is relocated to the rear of the engine valley. As far as I heard, it no longer activates transmission kickdown, that is done by the TCM in conjunction with the throttle position sensor.

it’s on the rear of the engine on A2 4 speed trucks, it’s on the left side of the injector pump for turbo trucks.
uses a cam on the throttle linkage

 

[Ranchtruck]

I'm at a loss My humvee 94 6.2L if I Rev the engine up the clutch fan engages. And a get a huge air leak burst sound. No oil leaks what's so ever. It's clearly not temperature induced. I can start it cold and it will immediately do it from revs. Not sure where to look to find anything on the subject previously. Sorry I'm new.

I'm having the same issue. At high rpm's the fan engages then disengages when I let off on the pedal. Thermal switch is good, Cadillac valve resistance checked good. The fan clutch engages/disengages when I disconnect/reconnect TDM. Were you able to fix your issue? Any info would be much appreciated!

 

[mccullek]

I just went through this issue with my own truck. The switch is actually closed when temps are below 220 and opens above that temp until engine cools down to 190 or so, then closes again. The cycle then repeats when and if your truck reaches 220 degrees again.

So the switch operates backwards from what you would expect. An open switch sends 24 volts to the Cadillac valve and turns on the fan.

If your TDM or switch fail, your fan will run constantly. The fail safe is to remain open if the system fails, so that would keep your fan running at all times.

You may not be able to detect it has failed in the fan on position at idle, and will prob only hear it or notice it when you increase the RPMs.

That’s how my truck was reacting. I replaced the thermostat and thermostat switch and no change. Turned out to be the TDM. As soon as I changed that out, everything worked properly.

Even though my fan was in the always on mode, it was not nearly as loud until I changed out the TDM. The first time my system operated properly, I was going down the hwy at 60 mph and when the fan kicked on, it was so loud I almost had a stroke. I thought the motor blew up!

Prior to that, it was running and loud, but nothing like when it is operating properly! It is literally louder than the motor at high speeds/rpm’s! Seems like they could have had a better design, but these things were not build for comfort or quietness.

 

[Mogman]

[QUOTE=". An open switch sends 24 volts to the Cadillac valve and turns on the fan.[/QUOTE]

Actually an open thermal switch removes the 24V to the cadillac valve turning the fan on, it is a fail safe system.

The reason is seemed so much louder is because before the fan was running all the time so there was no reference to how quiet it is when off, the sound was the same.