Fan not engaging at temps over 220

[mccullek]

With the warmer weather today, I took the M1097R1 out for a ride and today the temperature got well over 230 and the fan never kicked on.

I got out the TM and went through the steps. When I disconnect power from TDM, the fan kicks on, however, when I disconnect 458B from the thermostatic switch as described in the TM, the fan does not kick in, and the TM sends me to another set of checks.

I go through those step/checks and everyone of them checks out fine and it eventually stops and says “no fault,” but that can’t be true because the fan is not coming on and the test procedure to bypass the thermostatic switch does not kick the fan on.

I tested the temperature switch and it does close at around 220 degrees, so that switch is good. The fan also comes on when I disconnect power from the TDM.

What should I be looking at that would keep the fan from kicking on when I disconnect 458B from the temperature switch, which supposedly simulates a hot engine that should engage the fan, but it does not turn on the fan. I’m stumped!

 

[Mogman]

I would suspect a bad TDM.
BTW the temp switch should be closed at room temp, and open when it reaches around boiling point, removing the wire simulates the switch opening thus activating the fan.

 

[mccullek]

I would suspect a bad TDM.
BTW the temp switch should be closed at room temp, and open when it reaches around boiling point, removing the wire simulates the switch opening thus activating the fan.

Yes, I got continuity on switch when cold, and then no continuity when hot, so I had my description backwards.

 

[Coug]

If it isn't the temp switch, then it's the TDM.
The fan fails to engaged, so it has to have power to it to turn off.
Only two sources of power are temp switch and TDM. If it's not the temp switch, it's the TDM (provided everything is wired how it's supposed to be; I always feel the need to add a caveat like that because sometimes people do weird things with wires and electricity)

 

[mccullek]

If it isn't the temp switch, then it's the TDM.
The fan fails to engaged, so it has to have power to it to turn off.
Only two sources of power are temp switch and TDM. If it's not the temp switch, it's the TDM (provided everything is wired how it's supposed to be; I always feel the need to add a caveat like that because sometimes people do weird things with wires and electricity)

I’m gonna give the TDM a try, as the test steps had me testing all the wiring for continuity, ground and 24V and all of those wiring tests checked out good, and those test steps lead me to a no fault completion.

The no fault thing stumped me because obviously the fan isn’t kicking on. The only test that didn’t give me the expected outcome was unplugging 458B from the thermostat switch, as the fan didn’t engage as it should when disconnecting that connection.

I will come back and update this after trying the TDM for future reference.

 

[Coug]

I’m gonna give the TDM a try, as the test steps had me testing all the wiring for continuity, ground and 24V and all of those wiring tests checked out good, and those test steps lead me to a no fault completion.

The no fault thing stumped me because obviously the fan isn’t kicking on. The only test that didn’t give me the expected outcome was unplugging 458B from the thermostat switch, as the fan didn’t engage as it should when disconnecting that connection.

I will come back and update this after trying the TDM for future reference.

unplugging the cadillac valve engaged the fan, so that eliminated the cadillac valve as the problem.
Unplugging the Thermostat switch didn't make the fan engage, and you tested the switch itself and had continuity cold and open when hot, so it tested good.
The only other thing in the system that has 24V source is the TDM. From what I've read, it's the most common part to fail in the cooling system to begin with, but fortunately it's very easy to replace and not terribly expensive. Just make sure you order from a reputable supplier as I believe that's one of the parts that has a lot of chinesium knock offs on the fleabay and other less than reputable sources.

 

[mccullek]

unplugging the cadillac valve engaged the fan, so that eliminated the cadillac valve as the problem.
Unplugging the Thermostat switch didn't make the fan engage, and you tested the switch itself and had continuity cold and open when hot, so it tested good.
The only other thing in the system that has 24V source is the TDM. From what I've read, it's the most common part to fail in the cooling system to begin with, but fortunately it's very easy to replace and not terribly expensive. Just make sure you order from a reputable supplier as I believe that's one of the parts that has a lot of chinesium knock offs on the fleabay and other less than reputable sources.

Yep, the prices vary greatly and are about half price on the bay, so that leads me to believe there has to be a catch. I ordered from Hummer Parts Guy, so assuming he is a reputable source. I've purchased a couple of other items from him, so hoping he is considered a reputable source?

 

[Coug]

Yep, the prices vary greatly and are about half price on the bay, so that leads me to believe there has to be a catch. I ordered from Hummer Parts Guy, so assuming he is a reputable source. I've purchased a couple of other items from him, so hoping he is considered a reputable source?

Yes, he is definitely a reputable source.
MacMotors is another, along withKascar and genuinehumveeparts.com/
There are some more, but those are the main ones.

 

[mccullek]

I will just add that I ordered a fuel gauge from ebay and it was DOA. They sent me another one and I installed it and it is working, but it just felt lighter and much flimsier than the original, so I placed another order from another parts guy and it shows up today.

The new gauge was $20 more, but it looks and feels just like the original I took out. No comparison in quality, so you guys are so right about buying from reputable sources and paying a little extra! One thing I noticed that lead me to know it was a knock off is the casing has no way to let light through, so the gauge doesn’t even light up when you turn the gauge cluster lights on.

I’m embarrassed to admit it but I also bought a thermostat fan switch off eBay and it was DOA. That’s when I decided to stop buying from there. It is obvious I got a knockoff, so I just went back to the Hummer guy and bought another one that reads properly. I tested it to be sure before installing it! Going forward I’m not gonna worry about $20 or $30 differences as it’s not worth the extra hassle and need to replace it again right away.

Trust their advice on trying to save a few dollars and pay a little extra to get a good part when necessary.