fan not kicking on

[ken]

TCM was my typo. I should have typed TDM for time delay module. The little black box by the caddy valve. You are correct the transmission control has nothing to do with it.

 

[suzukovich]

There is one more way to check the Thermostatic switch. Pull it out and clean it up.. reinstall it.then see if it opens.

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[papakb]

Take the thermostatic switch out and put a multimeter on any resistance scale across it. Heat it with a hair dryer and see if it switches. It should change from open to closed and back when heat is applied and removed. Remember to test the right switch. The one behind the alternator is only for the temp gauge.

 

[Recon1172]

I had an issue where the fan always ran. The prior owner said the TDM was just replaced so I went the route of least money. I checked to make sure the fan was able to disengage first using 90 psi of air. It did. Then I unplugged the TDM the fan didn’t disengage. I pulled the Cadillac valve and ran air through it, but the fan still wouldn’t disengage. Then I replaced the cadillac valve first. Now the fan disengaged but wouldn’t engage when the temp climbed. Next I replaced the sensor in the crossover since it was also cheap. Still no joy. It ended up being the TDM. I replaced it and the fan engaged at 215 like it should. Everything with the fan operation revolves around the fan clutch, the crossover sensor, the Cadillac valve and TDM.

 

[1993]

Make sure all the air is out of the coolant lines. Since truck sat higher then the back. Sounds like there might be an air pocket near the thermostat. Next if been realy cold and the truck been sitting. Take a hair drier and run it blowing on the Cadillac valve. There is a possibility that it's stuck.. Next check the connections from the themostaic switch and or the switch is bad. One other thing. It wouldn't be unusual for the truck to have the wrong thermostat installed. This seams to be a common issue with former NG trucks. Also check the power steering fluid level. Fan clutch is activated by theCadillac valve when the Thermostatic switch sense the Temp is to hot and activates the the fan.. Also you need to really just drive the truck.

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OK
finally got around to getting insurance and registration, drove it on the road for the first time and the fan kicked on every time the gauge needle pointed straight up(I think that's about 220deg).
My thermostat might be ok, need to put new batteries in my laser thermometer.

I'm guessing that suzukovich was right about needing to "just drive it".
previously I had mostly just let it idle for 10-20min once a month(for about two years) with maybe a short drive around the yard. usually the fan would kick on if I let it idle long enough.
I'm definitely going to keep a close eye on it but hopefully it was something caused by the circumstances.
might attempt a drive to the inspection station tomorrow...

 

[papakb]

The fan should kick in somewhere between 230 and 240 but military gauges are build by the lowest bidder so you never know exactly how accurate they're going to be. If the fan kicks in at the same point every time the engine heats up you're probably good to go.

 

[suzukovich]

Fan will kick in at 220. Mine usually kicks in at about 215. But yes my experience is mil gauges are not always accurate.

The fan should kick in somewhere between 230 and 240 but military gauges are build by the lowest bidder so you never know exactly how accurate they're going to be. If the fan kicks in at the same point every time the engine heats up you're probably good to go.

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[Milcommoguy]

"Fan kicking on" (clutch locked-fan working) is really a good Cadillac valve solenoid, de-energized (no 24 volts applied) The logic here is backwards for many thinking something on is energized to work. That's is why un-pluging Time Delay Module TDM locks up fan (must have good working clutch and valve)

Engine running, Cadillac valve solenoid always has 24 volts applied do to temperature switch in water crossover that is normal closed (feeds TDM) until it reaches about 230 F then switch opens, removing power to Cadillac valve and removing PS pressure to clutch... then the fan kicks on. This switch is normally closed below 190 F +/- hysteresis.

That said failure of Cadillac valve solenoid (common, shorted coil winding's (should be 58 to 78 Ohms), then excessive current, then fail / blown TDM,) then fan always engaged are common issuse. Clogged-up & stuck valve could do it too.

Fan disengage also can occur when the "Kick Down Switch" at right side of injector pump (Peddle to the metal) is triggered to start a timed fan disengage... to enter a stream or get a boost of power from HP hogging fan.

Simple test measure resistance of coil 58-78 Ohms. If less, it is shorted! DO NOT connect TDM. If more, likely open. Any low resistance (<10k Ohms) from either lead to ground, toss it. Time for a new valve, test and then maybe new TDM. Also note coil and valve run warm to more than warm at coil.

Failure of any of these fan system controls / components assures that fan is engaged.

CAM

 

[1993]

"Fan kicking on" (clutch locked-fan working) is really a good Cadillac valve solenoid, de-energized (no 24 volts applied) The logic here is backwards for many thinking something on is energized to work. That's is why un-pluging Time Delay Module TDM locks up fan (must have good working clutch and valve)

Engine running, Cadillac valve solenoid always has 24 volts applied do to temperature switch in water crossover that is normal closed (feeds TDM) until it reaches about 230 F then switch opens, removing power to Cadillac valve and removing PS pressure to clutch... then the fan kicks on. This switch is normally closed below 190 F +/- hysteresis.

That said failure of Cadillac valve solenoid (common, shorted coil winding's (should be 58 to 78 Ohms), then excessive current, then fail / blown TDM,) then fan always engaged are common issuse. Clogged-up & stuck valve could do it too.

Fan disengage also can occur when the "Kick Down Switch" at right side of injector pump (Peddle to the metal) is triggered to start a timed fan disengage... to enter a stream or get a boost of power from HP hogging fan.

Simple test measure resistance of coil 58-78 Ohms. If less, it is shorted! DO NOT connect TDM. If more, likely open. Any low resistance (<10k Ohms) from either lead to ground, toss it. Time for a new valve, test and then maybe new TDM. Also note coil and valve run warm to more than warm at coil.

Failure of any of these fan system controls / components assures that fan is engaged.

CAM

Thanks for the detailed write up milcommoguy.

the issue seemed to have cleared up(at least for a little while) after I added power steering fluid(which was a bit low).
however, the problem seems to be back. but it really does seem to come and go.
can the cadillac valve or TDM fail intermittently?

Cadillac valve is at 64.1 ohms

When the system does work(as it did just now when I let it warm up), the fan kicks on at exactly 180degrees(gauge arrow pointing straight up).
Also, there is a hissing sound coming from under the dash area, this sound goes away when the fan turns on or when the steering wheel is turned all the way left or right.
The hissing also seems to go away after the truck has been driven for about 20min.

 

[papakb]

I just wanted to mention here that most failures with the Kysor-Cadillac valve are from failed coils and usually not the valve internals and that coil can be easily replaced for considerably less money than a new solenoid valve. Google "24V solenoid coil" and you'll find plenty of them under $50. If the valve itself fails it's usually due to crud in the system (like teflon tape) that can be cleaned out by disassembling the valve body.

 

[Thecaptain]

For what it’s worth, I was getting intermittent unusual fan on/off behavior. After a lot of troubleshooting (the tsm have good guides for checking each part of the system) my thermostatic fan switch was the culprit - it eventually failed so the fan was always disengaged.

The hissing noise is common, from my understanding, when the fan is disengaged and pressure is being applied to the system. I think bulldogger did something to minimize the noise.

Cap

 

[1993]

I just wanted to mention here that most failures with the Kysor-Cadillac valve are from failed coils and usually not the valve internals and that coil can be easily replaced for considerably less money than a new solenoid valve. Google "24V solenoid coil" and you'll find plenty of them under $50. If the valve itself fails it's usually due to crud in the system (like teflon tape) that can be cleaned out by disassembling the valve body.

What about the question I just asked?
intermittent...

 

[papakb]

The hissing sound your hearing is the power steering fluid moving through the Kysor-Cadillac valve. The easiest way to remedy that is to wrap a piece of an inner tube rubber around the valve inside the hose clamp.

There's always a chance that the valve is intermittently failing and they do wear out eventually. They aren't that difficult to disassemble. If you do that look for scoring on the solenoid plunger or possibly a broken spring.