How the fan/cadillac valve/time delay modules work

papakb

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I just posted this on the G503 site and thought it might be a fitting addition to SS for all those New-to-Me HMMWV owners.

This is one of the circuits in the HMMWV that is probably the most misunderstad because it works backwards from what your common sense tells you. The gold colored valve is referred to as the Kysor-Cadillac valve and when the engine is cool it is powered all the time to pass power steering fluid to the clutch on the front of the fan. This in itself is an oxymoron because the power steering fluid used is actually Dexron ATF (yes really!). This disengages the fan and allows the engine to come up to operating temperature. When the sensor in the crossover manifols detects the engine has reached ~230 degrees the Cadillac valve de-energizes and this allows the fan clutch to engage, cooling the engine down to around 190 degrees and then the cycle starts all over again.

The Time Delay Module (TDM) passes the power to the Kysor-Cadillac valve when the truck is turned on. After the engine reaches operating temperature if you momentarily floor the accelerator pedal it sends a signal to the TDM to disengage the fan for about 20 seconds. This is done so the fan isn't powered when the truck enters the water during fording operations. If the fan was powered the blades tend to snap off from the resistance of the water.

The TDMs are a common failure item and the general "fix" is to disconnect the 4 pin connector on it and this causes the fan to run all the time to cool the engine. When the fan is running it sounds like you have a 747 in the engine compartment but other than losing approximately 10 horsepower in a pathetically underpowered truck it won't do any harm to the engine, only your top speed!
:shock:


With the line from the Cadillac valve disconnected you can test the fan clutch operation by blowing ~90 psi air into it. When you do this you should see the fan move forward and backwards about 1/4". Beware of fluid blowing out of the hose if you release pressure too quickly.

If this is a new to you truck I strongly suggest you get online and download a copy of the Operators Manual, TM 9 2320-280-10. This has a lot of stuff you should know about the HMMWV before you get on the road. Download sites are all over the web and the manuals are free.


While part of the cooling system the temperature gauge is a seperate circuit and it isn't related to the fan system. The gauge sender is located in the left front of the engine block behind the alternator and drives the gauge directly.
 
Last edited:

Smckerigan

Member
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Scottsbluff nebraska
I just posted this on the G503 site and thought it might be a fitting addition to SS for all those New-to-Me HMMWV owners.

This is one of the circuits in the HMMWV that is probably the most misunderstad because it works backwards from what your common sense tells you. The gold colored valve is referred to as the Kysor-Cadillac valve and when the engine is cool it is powered all the time to pass power steering fluid to the clutch on the front of the fan. This in itself is an oxymoron because the power steering fluid used is actually Dexron ATF (yes really!). This disengages the fan and allows the engine to come up to operating temperature. When the sensor in the crossover manifols detects the engine has reached ~230 degrees the Cadillac valve de-energizes and this allows the fan clutch to engage, cooling the engine down to around 190 degrees and then the cycle starts all over again.

The Time Delay Module (TDM) passes the power to the Kysor-Cadillac valve when the truck is turned on. After the engine reaches operating temperature if you momentarily floor the accelerator pedal it sends a signal to the TDM to disengage the fan for about 20 seconds. This is done so the fan isn't powered when the truck enters the water during fording operations. If the fan was powered the blades tend to snap off from the resistance of the water.

The TDMs are a common failure item and the general "fix" is to disconnect the 4 pin connector on it and this causes the fan to run all the time to cool the engine. When the fan is running it sounds like you have a 747 in the engine compartment but other than losing approximately 10 horsepower in a pathetically underpowered truck it won't do any harm to the engine, only your top speed!
:shock:


With the line from the Cadillac valve disconnected you can test the fan clutch operation by blowing ~90 psi air into it. When you do this you should see the fan move forward and backwards about 1/4". Beware of fluid blowing out of the hose if you release pressure too quickly.

If this is a new to you truck I strongly suggest you get online and download a copy of the Operators Manual, TM 9 2320-280-10. This has a lot of stuff you should know about the HMMWV before your get on the road. Download sites are all over the web and the manuals are free.
Fantastic info! Thanks so much.
 

Milcommoguy

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Rosamond, CA
This should be at the top of the 'sticky" notes for new owners or anyone fussing with the cooling system. My little note is don't get confused with dash temp gauge or its sender. Separate system. Know where / how your kickdown switch works into the TDM.

Here's a very good video of how it works. Should clear up most problems. Take notes and pop some corn >
.

Been over this more than once, CAMO
 
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