M116A3 Build

[lfhoward]

Propex test fire!!!





Checked for propane leaks with soapy wooder (Philly / NJ accent, lol). Had one, tightened the joint and sealed it.
Next, I hooked up the 12 volt electrical with a 5 amp fuse. I turned up the thermostat, and turned it on.

What happened next was pretty much right on.
- Pause
- Fan motor starts
- propane solenoid opens
- multiple clicks of the igniter
- I can hear flames!!!

4-5 seconds later the propane solenoid closes and shuts down the flame. It goes out purposefully, not sputtering.

The question is, why? There are no error codes being generated with blinking leds on the thermostat.
Here are some of my ideas:
- thermocouple not sensing the flame?
- air to gas ratio or exhaust issues due to not having intake/exhaust pipes yet?
(The boards I have it on are separating the intake and exhaust from each other.)
- combustion chamber dirty/sooty?

Anybody with a Propex want to suggest a possible fix? Am all ears.

[lfhoward]

Ok this time I did get some sputtering. The flame went out before the solenoid turned off.

And we have an error code #2.



Sometimes it does this, other times it behaves like in the previous post. Either way the flame dies or is shut down by about 5 or 6 seconds.

[lfhoward]

Well, tinkered a bit. My Marshall gas regulator has a knob on it that allows the pressure to be changed. The stock position of the regulator would have been 11 WC. The British version of the Propex, which is what I have, calls for 15 WC (37 mbar). I have increased the gas flow a little at a time and have now gone 6 complete turns clockwise. I don’t have a manometer to measure the gas pressure but the flame sounds much healthier now. It never quits on its own and is now only shut down by the gas solenoid. Unfortunately that still happens.

Does the Propex have a thermocouple? I’d like to find it and test it.

[MickinOz]

You can make a manometer if you really need one.
Get yourself about 3 yards of 1/4 inch I.D. clear plastic hose and a 4 inch wide board about 2 feet long. Use 4 feet or so of one end of the hose to form a long narrow U shape on the board. Staple/pin/tape the U as straight as you can get it, taking care not squash the tube. Should have one end stopping at the top of the board, and one long tail for hooking up.

Hang the board as vertical as you can get it and about half fill the U with water and mark the level with a marker. Mark inch graduations either side of the mark.
You now have a U-tube manometer that is surprisingly accurate.
I once saw an engineer who found himself bereft of a commercial unit use such a device to find out which huge industrial fan was not pulling its weight.
"That one there boys, its way off the pump curve". And he was right.

Take the long end of the tube and hook it to your gas supply.
The water in the U should be pushed away from the zero mark.
Count the number of graduations between the high and low levels of the water columns. Or just measure the differential.
That's the pressure in inches of water column.
If you used about 4 feet of hose, and you managed to fill exactly halfway, you get to measure up to about 24 inches of water column before the gas blows the water out of the tube.

[lfhoward]

Thanks OZ. It would be interesting to see the actual gas pressure after the regulator and that would be a cool way to do it.

My working hypothesis right now is that the thermocouple is bad. (The light blue wire goes to it, and it’s located to the left of the burner. The right side is the igniter.)



I think the thermocouple may be bad for several reasons.
- The heater shuts itself down and closes off the gas as if there is no flame, even though there is.
- My multimeter shows the thermocouple sometimes makes less than 5 millivolts when I hit it with my butane lighter. What I am seeing online in my research is that a thermocouple should produce 30-40 millivolts, although that’s generic and not a Propex specific number. It jumps around and occasionally spikes higher (like 50-80 millivolts) but that’s intermittent and then it’s gone.
- I can occasionally trick the heater into running for longer than 6 seconds on the bench simulating a flame directed right on the thermocouple with my butane lighter. It’s really hard to keep it going this way though.

[elmo_cecil]

hey hey new to the forum... just wanted to say hi

great build... im working on a camper based off of an m116 right now... im also working on buying and putting a furnace in (but going with a diesel one)

any word from the wise for me?

[lfhoward]

hey hey new to the forum... just wanted to say hi

great build... im working on a camper based off of an m116 right now... im also working on buying and putting a furnace in (but going with a diesel one)

any word from the wise for me?

Hello! I just checked out your photo album and I like your trailer. Would the style be considered a Vardo?

A couple of things I've noticed building on the M116:
- All the angles on the trailer won't be perfectly square (due to usage by the Army, probably), so you have to adapt your plans accordingly. The bed on mine was actually bowed where it was tallest in the center above the axles. One side of the front was lower than the other.
- It's worth fixing the surge brakes and making sure they work. It's a heavy trailer and the brakes really help. Use Dot-5 silicone brake fluid, not the Dot-3 that your car/truck uses. Croft Trailer Supply has all the parts for the surge brake apparatus if anything needs replacing. (I have part numbers somewhere on my build that you can reference.)
- I replaced the military tires and rims with ones from a GMC pickup truck of the same era, and it lowered the trailer enough to make it easier to tow but also get into and out of.
- Anything you need that is military trailer specific can be found on the Steel Soldiers forum. You can download the Army's technical manual for the 101/116 trailer there, which has all the part numbers and maintenance procedures.

Hope some of this is useful! If you ever have questions just feel free to ask.
Lauren

[lfhoward]

Back to the Propex for a second. I had some snippets of time today where I could run a few tests. First I cobbled together a platform to mount it on with some scrap pieces of wood, which keeps the intake from sucking up exhaust gasses. Here are the results:

1. It's not a weak battery causing the issue. I hooked the battery up to the charger while running the Propex and verified we were above 13 volts. It still shuts down after 5 seconds.
2. I put my multimeter on the blue wire and a ground to measure millivolts from the thermocouple. It was all over the place. Not sure what it should read.
3. I found a little red LED on the motherboard that mimics the error light on the thermostat. It's much easier for me to see. We are pretty consistently getting the 2 blink code, even when the Propex shuts itself down (not just when the flame sputters out on its own). Code 2 is a flame sensing error.

[featherliteCT1]

So do you think you will be able easily to source a new thermocouple?

[lfhoward]

So do you think you will be able easily to source a new thermocouple?

That’s a good question. It doesn’t seem to be searchable on the web.

I have a conversation going with the support person for Propex heaters over at VanCafe in Colorado, and I contacted Propex UK last night also. Hopefully between the British home office and their US distributor, I will be able to get one. And then there is the next question, is that what was wrong in the first place and will it fix the heater?

It’s all part of the adventure of buying a known broken heater for a fraction of the cost of what a new one would be.

[elmo_cecil]

hey hey new to the forum... just wanted to say hi

great build... im working on a camper based off of an m116 right now... im also working on buying and putting a furnace in (but going with a diesel one)

any word from the wise for me?

Hello! I just checked out your photo album and I like your trailer. Would the style be considered a Vardo?

A couple of things I've noticed building on the M116:
- All the angles on the trailer won't be perfectly square (due to usage by the Army, probably), so you have to adapt your plans accordingly. The bed on mine was actually bowed where it was tallest in the center above the axles. One side of the front was lower than the other.
- It's worth fixing the surge brakes and making sure they work. It's a heavy trailer and the brakes really help. Use Dot-5 silicone brake fluid, not the Dot-3 that your car/truck uses. Croft Trailer Supply has all the parts for the surge brake apparatus if anything needs replacing. (I have part numbers somewhere on my build that you can reference.)
- I replaced the military tires and rims with ones from a GMC pickup truck of the same era, and it lowered the trailer enough to make it easier to tow but also get into and out of.
- Anything you need that is military trailer specific can be found on the Steel Soldiers forum. You can download the Army's technical manual for the 101/116 trailer there, which has all the part numbers and maintenance procedures.

Hope some of this is useful! If you ever have questions just feel free to ask.
Lauren

yeah the angles thing threw me for a bit of a loop.. but not too bad..

mine must have been older as it didnt have surge brakes only hand operated e-brakes and the old 5-lug bud split rims... tires dated 1960..

i replaced axle with a dexter 3500lb unit and no brakes saved a bunch of weight and also set it up to use same rims as my tow vehicle (same size tires too) so i only carry one full size and one compact spare.

what does your weigh in at?

oh and you might try mcmaster-carr or digikey for a thermocouple... my thoughts are "if its electrically equivalent... make it work"

[lfhoward]

Propex heater update.

I got it hooked up to my grill canister, and got the gas regulator dialed into exactly 37 mbar (UK units, 15 WC here) which is what the heater needs. It fires, burns strong, and then shuts down after 5 seconds.

I disassembled and extensively tested the components of my HeatSource 1600 and believe I have identified the problem.

I have ruled out:
- Gas pressure is in spec
- Gas solenoid works
- Fan blows strongly
- Air speed sensor spins fine
- Sparker works effectively
- The unit always lights, burns strong for 5 seconds, then shuts off automatically. It tries one more time, then shuts off. I get two flashes for the error code, which in the HS1600 model is a flame sensing error.

I carefully removed the thermocouple and tested it on the bench. This is the part I believe is faulty.
- Part of the ceramic insulator was damaged
- There is no continuity or resistance between the spade terminal and the mounting screw ring
- There are not any millivolts produced by the thermocouple when I heat the rod with a butane lighter





I wrote to Propex’s customer service in Britain (since this is a U.K. spec model) and asked them to send me a new thermocouple. Fingers crossed!!!

[lfhoward]

So with more research I figured out that thing in the photo is called a flame sensor not a thermocouple. It doesn’t have a ground. Flame sensors can be cleaned, so I polished the rod with steel wool and a scotch brite pad. Now I have conductivity between the rod and the spade terminal, and it makes millivolts when I put my butane lighter on it. It doesn’t register any milliamperes though. Still having issues keeping the heater running even having cleaned this, so the problem is not yet solved.

[lfhoward]

Ok I did some more experiments and this time I’m sure the flame sensor is at fault.

- I removed it and cleaned it again extremely well with a scotch brite pad. There was great continuity between the rod and the connector now. I noticed that the insulator was chipped and possibly has a small crack.



- I reinstalled the cleaned flame sensor and ran the heater, but with my multimeter in series between the flame sensor wire and its pin on the circuit board. No micro amps were detected at all, but I got .3-.5 volts, which seems kind of high. A working flame sensor should produce 5-10 micro amps based on my internet research.

- Going on the assumption that the heater was looking for a few micro amps to keep running beyond 5 seconds, I changed my multimeter to the ohms setting. The multimeter sends a tiny bit of current to check for continuity and resistance in this mode, but a tiny bit of current was all that was needed. The heater ran for 15-20 seconds this way and I turned it off manually. It got nice and hot.

Ah-ha! My conclusion is the flame sensor has to be bad because it doesn’t send any micro amps to the ECU. It could be possible a hairline crack in the porcelain insulator is allowing it to ground out. That chip/crack is suspicious.

I could be wrong about the sensor being bad if the flame is the wrong length and not contacting the flame sensor rod, but the rod is positioned in such a way that it must contact the flame.

I have at least ruled out the possibility that the problem was with the ECU/motherboard. That’s a relief!

[edit: I can’t use the multimeter in ohms mode on the bench to fool the heater into staying on in the absence of a real flame. Going to see it it was actually working and try to fire it up again tomorrow to see if it will stay on.]

I took some measurements of the flame sensor. I can’t find this exact one online, but I can find a similar one with a straight rod that I could probably bend to the correct angles. That or try harder to get the right one from Propex UK. Maybe I should give them a call, because I don’t seem to be getting through via their support email.

[lfhoward]

Learning things all the time. Here is a really good reference on how flame sensors work:

https://www.hvacrschool.com/flame-sensing-the-basics/

One thing I learned is that the direction the electric current should flow is from the ECU board to the sensor, through the flame, to the burner housing to ground. So me putting the multimeter in series between the board and the sensor should not have any effect on ohms mode except to connect the circuit through the flame. So there is a hope the flame sensor actually worked that time the flame stayed on and me having the multimeter there was a coincidence. Of course this circuit would not be completed with no flame and so there is no way to trick the ECU in the absence of a flame on the bench. This also explains why there is no current produced when I try to use my butane lighter on it - no connection back to ground.