Fan not cutting on

[kfrosty]

I've got my second Hmmwv out of 5 so far that the fan doesn't kick on at 215 or whatever.

The only things that effect this are the temp sensor in the water cross over, the Time Delay Module and the Cadillac valve, correct?

If I unplug the connection to the TDM, then the fan comes on and stays engage.

My understanding if one of the above was bad then the fan would stay engage. But it's just the opposite. So I thought it would be the Temp sending unit in the cross over. I've changed that out with a couple of others. (I just ordered to new ones to be sure.)

Has anyone had a similiar issue and it turned out to be the TDM or cadillac valve? I'm assuming it's not bad because the fan will come on if I unplug the TDM.

Thanks

 

[Mjvaden]

It is the temp switch or the TDM. the cadillac valve supply fluid to the fan clutching cuts the fluid to the clutch when the tdm says to thus engaging the fan. so if the fan engages when you default it (unplug) then the valve and clutch are good.

 

[kfrosty]

Thanks. Hopefully it's the temp switch.

 

[gcbennet]

I've recently begun to experience the same problem as well. I tested the temp sensor using the hot water method and it works as it should. I then swapped the TDM with another one I had, but that didn't solve the issue either. At this point out of process of elimination I believe the Cadillac valve is the culprit and, of course, it's the most expensive to replace of the three components. I'm going to pull the valve and fiddle with it a bit to determine if something is either interfering with the normal mechanical operation, or if it is an electrical issue with the solenoid itself.

 

[kfrosty]

Does your fan come on if you unplug the Temp sensor or TDM connector?

I'm not sure how it works but the fact you unplug something to get it to come on makes me think that there is a current that keeps the Cadillac valve closed. When the is no current, it opens.

That's why I have a hard time believing it could be bad if it works when you break the circuit.

 

[gcbennet]

Yes, the fan comes on when I unplug the TDM as it should. The system is designed to default 'on' if there's a problem to prevent overheating, but for whatever reason my system believes it's working properly even though the fan does not come on when it should. Obviously the Cadillac valve is operating since it still controls fluid flow to the fan when I plug and unplug the TDM connector, and the fan itself engages and disengages properly. I'm not sure what to do at this point short of swapping out components until the problem goes away.

 

[gcbennet]

Well, it happened. My truck has finally made up its mind and the fan has now defaulted to the full-time 'on' position. Since I've now lost a good chunk of my horsepower I'm motivated to begin troubleshooting the culprit. lol

 

[joeberg]

If fan is stuck on, I would short the wires connecting to the thermostatic switch. If the fan cuts off when shorted, replace the switch. If not, replace the TDM. May want to check grounds also if you haven't already.

 

[kfrosty]

I replaced the thermostat switch in with a new one in one of mine and now the fan started working. However, it's in the 90's, I think I like the fan running full time and the engine temp staying under 200.

I've had my radiator flushed and gone through and these do not run under 200 around here in 90 degree days.

 

[gcbennet]

I suspect the TDM is the culprit once again since I tested the temp switch using the hot water method and it's serviceable. However, there's some good electrical circuit tests illustrated in the 'Component Testing and Troubleshooting' leaflet (5715434) that cover all of these components and will prove to be helpful.

 

[papakb]

18 years ago when I got my HMMWV there wasn't anyone to talk to about problems and we basically had to solve our own issues. Now with the advent of great forums like this and the G503 we don't have to keep reinventing the wheel. This was my early solution to this exact problem. T

 

[papakb]

18 years ago when I got my HMMWV there wasn't anyone to talk to about problems and we basically had to solve our own issues. Now with the advent of great forums like this and the G503 we don't have to keep reinventing the wheel. This was my early solution to this exact problem. This is a 3 position switch that in the down position is in automatic mode. The middle position is the fan never on and the top position is the fan always on. After working thru the issues discussed here and resolving the problem I left it in place, mainly 'cause it looks kinda cool.

Kurt
KG6KMJ

 

[KRedd]

http://www.steelsoldiers.com/attachment.php?attachmentid=601025&d=1378950635&thumb=1