Q: How does the Fan "Sensitivity Switch" Work?

[FlameRed]

Yet another question for the collective.

I did scan the electrical diagram I have for the M998 but I am not seeing this Fan Sensitivity switch.

After converting my TH400 to a 4L80, I moved the Fan Sensitivity Switch that was located on the throttle body, to the back of the engine. I used the old switch and other no longer needed parts into something that lookes like one of these:

The M998 has AC, and I used to hear the "helicopter" fans turn on. Now I don't hear them turn on.

How does this circuit supposed to work? I assume that when the throttle is at idle, or under low load, the fans should come on. This switch is supposed to prevent the fans from coming on at high loads preventing the engine being bogged down due to generator electrical demand from the fans.

So I put a VOM on the two leads, with engine on. One lead seems to have +24V with the engine on. The other lead seems to have two resistance readings. With the throttle at idle position, there is something like 12k ohms from the other lead to ground. With the throttle at WOT, this second lead seems to have infinite resistance to ground. Is that what is expected?

If I short the two leads, the fans still do not come on with the engine running (hot).

If so, what should I look at to figure out why the fans on top the AC condenser do not seem to come on whereas they used to come on before I tinkered with this switch?

It could be I somehow damaged the switch when I removed it from the throttle body shaft. How should this switch be tested?

Thanks in advance!

 

[Mogman]

The HMMWV never had electric fans.
The switch on the throttle was to put the fan control in delay so when you went into the water it did not rip the belt driven fan blades off, it may have also been designed to delay the fan when at WOT but never did that on my M998

 

[FlameRed]

Thanks - so I will have to trace the wiring on the condenser fans back and figure out how they hooked it up. Just coincidental they stopped working with that switch change.

 

[Mogman]

I suppose it is possible they connected it to kick off the compressor and fans under WOT but I would think the AC would not work at all.
Does it still blow cold air?

 

[FlameRed]

I suppose it is possible they connected it to kick off the compressor and fans under WOT but I would think the AC would not work at all.
Does it still blow cold air?

Well, I am fighting two issues at once. Yes, it can blow cold air but the Freon is low. It has a leak in the EVAP which I am going to swap out as soon as the part arrives. Confirmed with a Freon leak detector.

I would have also thought they should be on constantly with the AC on, but that is not how the condenser fan behaved before I changed the switch position off the throttle body plate. Those fans seemed to go on with the AC on, truck running full temp, and low throttle. The fans did not seem to run constantly with the AC on.

Perhaps I should change that so the fans run with the AC compressor on if that is how I find it wired when I trace the wiring.

EDIT: After a bit of wiring chasing, I found the relay that was installed which triggers the compressor and the fans. Looks like they used speaker wire!

I found that AC compressor wire was ok, but the fan wire was all corroded and disentegrated where it contacted a spot on the hot condenser. So a simple repair usning good wire, new relay, and the fans kick on with the AC now.

On to fixing the leak in the evaporator...