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Old 05-14-2015, 08:00 PM   #11
Bus Crazy
 
Join Date: Feb 2012
Location: Salt Lake City Utah
Posts: 1,328
Year: 2000
Chassis: Blue Bird
Engine: ISC 8.3
Is the time-to-shutdown consistent from one test cycle to another? Can the blowers be re-started immediately? Myself and cowlitzcoach are understanding your question to mean the blowers on those water-to-air heaters are shutting down; if something else is meant please say so..

I'm not so sure about the lazy relay theory. I'm trying to think of a time when I heard of relay contacts opening unexpectedly, ie without the coil current being interrupted, and I just can't come up with anything. There's some self-heating inside the relay, and I guess since copper has a positive temperature coefficient its resistance goes up (and relay coil current goes down) as it heats, but it also takes much less current to hold a relay than to pull it in..

What about a circuit breaker? My Blue Bird has a panel of a dozen or so self-resetting circuit breakers. These are thermal-operated breakers -- current through the breaker causes heating, and sufficient heat causes the breaker to open (bimetallic strip internally, probably?). If the overcurrent is extreme it'll open pretty fast, but if it's only slight it could take minutes or even hours before it opens. After some time it cools and recloses automatically.

It isn't unheard of for motors to develop shorts in their windings. A partial short could cause a motor to still run but at higher current than it should and could in turn trip supply protections like a breaker or fuse.

OP probably will need to trace wires from the fan switch and test with a light or meter to find out whether the switched output changes even without throwing the switch, and if not, then continue downstream to see what comes between the switch and the motors and find where things open up on their own.
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Old 05-14-2015, 08:19 PM   #12
Skoolie
 
Join Date: Mar 2015
Posts: 231
I think I have found an operating manual for your heater, if not you may be able to go to the vendors website and find the one you need.
http://www.nelsonsbusservice.com/dow...structions.pdf

you may have issues with multiple parts of this heating system, you will need to take it one step as a time and figure out each piece.

the good news is this is how you get to know your machine and learn and in the future will know what the likely issue is because you are failure with so much of it.

good luck
Cliff
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Old 05-14-2015, 08:36 PM   #13
Bus Crazy
 
Join Date: Jul 2011
Location: Winlcok, WA
Posts: 1,607
I when I called them lazy relays what I should have said was resistors.

In some buses, Thomas comes immediately to mind, instead of having multispeed motors they used resistors to step the voltage up or down to vary the speed of the blower motors.

Those have been known to fail and will allow the blowers to run for awhile until they warm up and then they lose contact.

After a period of time they will be cool enough for the blowers to start working again.
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Old 05-14-2015, 08:43 PM   #14
Bus Crazy
 
Join Date: Feb 2012
Location: Salt Lake City Utah
Posts: 1,328
Year: 2000
Chassis: Blue Bird
Engine: ISC 8.3
Ah, now I understand what you mean. That's a very good idea to look for something like that. The same resistor trick is common in passenger cars too. In cars I've seen them mounted in the air handler box so that the resistor (often a bare coil of wire, easily mistaken for a spring) is cooled by the air that's blowing through. If it's broken, self-heating could cause the resistor to bend until finally the cracked spot separates and then the motor stops just like you described.

Where does Thomas hide them? Somewhere in the blower housing, I guess... or buried in the big wiring panel?
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Old 05-14-2015, 09:05 PM   #15
Skoolie
 
Join Date: Mar 2015
Posts: 231
Quote:
Originally Posted by family wagon View Post

Where does Thomas hide them? Somewhere in the blower housing, I guess... or buried in the big wiring panel?


I am not sure if this is relevant to this conversation, but I have some resisters soldered inline right at relays on my bus. it is a 95 year model

thanks
Cliff
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Old 05-18-2015, 06:30 PM   #16
Mini-Skoolie
 
Join Date: Jul 2014
Posts: 46
Quote:
Originally Posted by cowlitzcoach View Post
Idling your bus, even at fast idle, for 20 minutes is a recipe for engine failure.

With no load the engine will never really get warm. When the engine does not get up to operating temperatures you don't get full fuel burn on each cycle of the piston. The unburned fuel tends to wash past the rings and will start to dilute your lube oil. It will also tend to coke up your exhaust system reducing your turbo efficiency.

If you want to run the bus then every month or so take it out on the road and give it a work out. Ten miles would be the minimum if the route included a good hill where the engine would get a workout or several miles at highway speed. For that matter, take it camping and use it as a tin tent if you can. But don't just run it in place!

If the blowers blow and then just shut off that tells me you have a relay that needs to be replaced. So that the full load of the appliance doesn't go through the switch relays are used to carry the full load of the appliance. Over time they get lazy and will shut themselves off. If you waited ten more minutes they would probably start right back up again.

Find a good hot lead that is full of juice and put it directly to the fan wiring. If the blowers keep blowing longer than they do now you will know you have a bad relay somewhere between the blowers and the switch. If the blowers cut out then you will know you have a bad set of blower fans.
I did not realize this. Thank you for the heads up. I don't have it registered right now, and even though I have it out in the middle of nowhere I really don't want to go drive it around unregistered and uninsured. I've been trying to start it up and let it run every few months for 30 minutes or so just to make sure it gets a little use.


Quote:
Originally Posted by c_hasbeen View Post
you should have a wiring schematic on the inside of your access door, you may study it for a little bit and figure out wire colors and circuit numbers that will help chase down a relay.


now that I think about it the schematic will not show the wiring diagram for any thing other than the heater fans inside the cabin, the separate webasto wiring schematic will not be on that access door cover.
good luck
Thanks, I'll check it out.

Quote:
Originally Posted by family wagon View Post
Is the time-to-shutdown consistent from one test cycle to another? Can the blowers be re-started immediately? Myself and cowlitzcoach are understanding your question to mean the blowers on those water-to-air heaters are shutting down; if something else is meant please say so..
I didn't keep trying it too many times, but it seemed that it ran for 5 minutes, then shut down, and would restart every time I flipped the switch, but then die within 30 seconds. And yes, it's the blowers on the rear heater (not Webasto) and the blowers in the front (drivers heat).

Quote:
Originally Posted by c_hasbeen View Post
I think I have found an operating manual for your heater, if not you may be able to go to the vendors website and find the one you need.
http://www.nelsonsbusservice.com/dow...structions.pdf
Thanks, Cliff!
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