Stewart Warner Vehicle Multifuel Heaters

[Boathook36]

I recently bought a pair of Stewart Warner 10560 heaters. Mine are the 10560M24B1 type. This forum had the publication TM 9--25540-205-24&P that details a great deal of good information about the heater itself. The wiring diagrams are pretty lacking, however, and the control box itself is not detailed at all. The first heater I tried to start had no power to the blower or igniter because of a previous owner mixing up the wiring in the control box. I'll post pictures of my progress here. If anyone else has experience with these heaters I'd like to hear about it.

I'm especially curious to hear about the military application of them. It seems like this upright version of the unit with the integrated fuel tank above it was used in the interior of certain armored vehicles like the Bradley. As near as I can tell there was a HUMVEE 30K BTU version that's basically just my 60K BTU unit but just stuck in low range. Those seem to have mounted horizontally with their fuel pump and fuel filter separate. It seems like they might have been used in the 2.5 ton trucks but I can't tell if they were mounted underneath or if they used the upright unit like I have.

I was told that you should always start it in High range but don't see any mention of that in the documentation so far. I can see that the switch itself is a simple on off switch that is only energized when the light is on, which also indicates the flame sensor has closed, which also opens the power to the ignitor. As near as I can tell it doesn't matter what position the high low switch is in while starting it.

 

[Boathook36]

Here are my rough drafts for the electrical schematics. The ones on the side were damaged but between the two I think I have an exact copy. I'll make a CAD version once I'm confident in its accuracy.

 

[Guyfang]

If you are looking for parts, please start a "Parts Wanted" thread.

 

[Boathook36]

The purpose of this thread is discussing how to support these units, not to source parts. I will detail the interchange or availability of alternative parts that work in lieu of the original hardware here as I figure things out.

I already found an error in my previous posted draft of the control wiring diagram since the upper pins behind the "Run" position are actually the outputs for the "Start" position and vice-versa. The wires are correct as drawn but the Run and Start labels were reversed.

My goal is to rewire the control box to make the former "Run" switch position the "High" position and the former "High/Low" switch to be a "Run" switch. There is an awkward and sudden need to cycle from "Start" to "Off" to "Run" as soon as the bulb turns on. The bulb turns on with the Flame Switch hot enough to open the contacts to the Igniter. The blower motor runs off the Igniter until that switch opens and then it closes battery power directly to the blower. This means the Run switch doesn't actually control the Blower at all. It really just controls the Fuel Pump. That's why jumpers connect three of the six pins together. Half of the double pole switch is just dedicated to turning the fuel pump on. The reason they made the "Start" switch opposite the "Run" switch is to prevent the fuel pump running before the unit was hot enough to trigger the bulb unless someone was actively depressing the momentary switch and likewise triggering the ignitor to try to ignite the fuel from the fuel pump. I think I can change the feed to the alternative Run Switch to follow the same logic with easily reversible changes to the diagram.

I see quite a few Stewart Warner heaters that are missing their control box. The proposed changes would also make it easier to make your own control box from scratch if you come across a unit missing the original hardware.

Both of my heaters have bad flame detector switches. I have a third spare one that is also bad. It seems to be as simple as corrosion on the internal switch contacts. They seem simple to rebuild, tho I have to cut off the rusted bolt and replace the spring to get it open. I might just measure the prior adjustment gap and set it at the same gap. The manual references an adjustment procedure but I haven't found specifics yet. I'm currently cleaning off all the rust and putting never-seize on every fastener throughout the units.