LMTV cabin fan not working

[derpschitz]

Cabin fan won't work anymore. Attempting troubleshoot. Manual says it's on CB8, but that doesn't exist on the breaker panel. Is there another panel hidden somewhere?

 

[Ronmar]

Exactly what vehicle is this on? A M1079 habitat fan? what are you using for an AC source to the box and where/how is it connected? CB8 for that fan would be in the enclosure power panel in the M1079 box.

Now if you are referring to the heater blower in the cab that should be ignition 24v from CB23 in the cab power panel...

Again, all tech questions should include exactly what vehicle you are working on, so we can all start out on the same page.

 

[derpschitz]

Exactly what vehicle is this on? A M1079 habitat fan? what are you using for an AC source to the box and where/how is it connected? CB8 for that fan would be in the enclosure power panel in the M1079 box.

Now if you are referring to the heater blower in the cab that should be ignition 24v from CB23 in the cab power panel...

Again, all tech questions should include exactly what vehicle you are working on, so we can all start out on the same page.

M1078, sorry should have specified. It is the blower in the cab. Also it seems the engine-driven radiator fan is stuck "engaged" again, may be related. Had worked fine before after I replaced the air solenoid.

 

[Ronmar]

A0 or A1?
yea the diagram you showed is for the m1079 habitat box... the dash heater blower is powered from CB23 in the dash. 24v from power panel ignition relay to breaker, to dash switch, to fan motor and back to TB2(ground TB) in(under) the power panel to complete the circuit.

CB22 provides power for the engine fan circuit. removal of power disables solenoid to engage fan. On an A0 the thermal sw in the upper rad pipe removes this power. On an A1 the ECU does it.

What happens when you use the fan disable/fording switch upper left on the dash? This should provide CB22 power directly to the solenoid bypassing the thermal sw/ECU control to energize the solenoid and release the fan..

 

[derpschitz]

A0 or A1?
yea the diagram you showed is for the m1079 habitat box... the dash heater blower is powered from CB23 in the dash. 24v from power panel ignition relay to breaker, to dash switch, to fan motor and back to TB2(ground TB) in(under) the power panel to complete the circuit.

CB22 provides power for the engine fan circuit. removal of power disables solenoid to engage fan. On an A0 the thermal sw in the upper rad pipe removes this power. On an A1 the ECU does it.

What happens when you use the fan disable/fording switch upper left on the dash? This should provide CB22 power directly to the solenoid bypassing the thermal sw/ECU control to energize the solenoid and release the fan..

Fording switch has no effect on stopping the radiator fan.

 

[Ronmar]

Fording switch has no effect on stopping the radiator fan.

well then it is either a power source issue or perhaps the solenoid is not working. what solenoid did you put in it?

 

[derpschitz]

well then it is either a power source issue or perhaps the solenoid is not working. what solenoid did you put in it?

The solenoid is the one from callmecolt. I'd guess power source issue considering the cabin fan is not blowing either. Gotta dig some more.

 

[Ronmar]

The solenoid is the one from callmecolt. I'd guess power source issue considering the cabin fan is not blowing either. Gotta dig some more.

That solenoid has a LED indicator in its plug that shows when it is receiving power. It and the solenoid itself should cycle on and off with the ignition sw.

If there is more than ~85PSI in the wet tank the solenoid should send that air down to release the fan clutch when energized…

 

[derpschitz]

I tested CB23 with a 30A fuse, no joy. Fuse was fine. Need to test and see if there is power to that breaker.

 

[Ronmar]

I tested CB23 with a 30A fuse, no joy. Fuse was fine. Need to test and see if there is power to that breaker.

Yep. CB23 feeds right to the control switch for the heater. With a volt meter you should see 24v on one terminal of the CB23 socket with the ignition switch turned on.

What year is this truck? be careful overfusing, especially on the A1's with the circuit board power panel. fuses are intended to protect the circuitry and bigger is not better, unless you like smoke...

 

[derpschitz]

I don't plan on overfusing, just troubleshooting to see what works and what doesn't. Truck is 1998

 

[Skyhawk13205]

My cab heater fan wasn’t working when I got it from auction, I did a voltage check and I was getting about 12v to the fan switch, found the plug behind the heater was corroded, I replaced with a deutch type plug.

 

[derpschitz]

Finally got around to addressing these issues. Fuse block is fine. Breakers are fine. Proper voltage is running to the pins. No joy on the cabin fan but I do hear something click and hiss in the radiator fan solenoid area when I play with its breaker. Maybe something is disconnected in there. Will look deeper.

 

[Ronmar]

well if the cooling fan solenoid is clicking and hissing that is a good sign. the wet tank needs to be above 85PSI in order for its protection valve to send any real airbeyond leakage) to the fan solenoid or CTIS. If you start the truck and get to full air pressure when you shut down the ign sw, that cooling fan solenoid should give you a good woosh as it releases the air holding the fan clutch disengaged. if after shutdown, you turn the ign sw on then off, you should get another woosh as it first charges the fan clutch with air(ign on), then releases that clutch air(ign off). you should be able to do this till the wet tank once again drops to ~85 PSI...

Do you have an Ohm meter? From that cabin fan connector you rebuilt, with the fan switch on high, you should be able to measure the circuit resistance thru the fan switch and motor from that connector...

"Voltage is not considered good until tested under load"!

The problem with simple voltage checks is that they do not take into account poor connections. A bad/high resistance connection will deliver full voltage unloaded to the end of the circuit, but resistance resists current flow, not voltage, so as soon as you try and pull current thru that bad connection, like a kink in a garden hose, the resistance will still let full pressure build at the end of the hose, but once you open the valve at the nozzle, the kink will restrict flow and cause a drop in the voltage(pressure) felt at the nozzle on the end of the hose...

 

[derpschitz]

Popped the cabin and found some "interesting things". RATS. Engine covered with turds, air line to radiator was chewed off. Also found similar air lines on top of engine that lead to a couple of whatchamacallits, not sure what those are but I need to replace at least one of those lines because they are chewed to hell. Just melted the plastic out of the flare fitting for the radiator, will patch that up shortly and see how that does.
What size is this tiny air hose so I can do a fix? Thanks!

 

[derpschitz]

Do you have an Ohm meter? From that cabin fan connector you rebuilt, with the fan switch on high, you should be able to measure the circuit resistance thru the fan switch and motor from that connector...

I didn't rebuild my cabin fan connector, that's a different guy on a different thread. I'm still trying to diagnose why the fan won't come on at all. I'm good with volts and amps but ignorant on ohms, I do have a really good voltmeter with ohmmeter. Considering the other stuff that happened, my first guess is the wiring is rat-chewed somewhere. I don't know where to look though.
Those SOBs trashed my motorcycle AND my LMTV this winter.

 

[derpschitz]

Radiator fan airhose fixed, it's all working as it should. Cabin fan still a mystery. Is there a diagram somewhere how it's put together? I got all the screws off the case and nothing will budge, I don't want to force anything because I don't want it to break. What would be the easiest way to get the fan speed knob out, or at least get access to its rear wiring?