SW 60k BTU Multifuel Heater, Not Working, Won't Light

[74M35A2]

Anybody have experience working with the SW 60k BTU fuel fired heaters? I have one that won't light. Power and fans are ok, but when held in start position, I don't see or feel the fuel solenoid clicking, and smoke comes from the fuel pressure regulating chamber, seems there is a heater in there? I don't think there should be smoke though...

I need to read the manual on it, but it covers all models, so I thought I would try to see if anybody has a really good understanding of how they work for pointers.

 

[cranetruck]

The fuel control valve does have thermostatically controlled heaters, but they should not get very hot, perhaps 70°F or so (not enough to produce smoke).
Not familiar with the newer models that are "transistorized" and use an on-off modulating control valve, the clicking noise you refer to.
How long do you keep the "ON" switch on, it usually takes minutes to get these things going?

 

[tractors0130]

How long are you holding the start button? On my M925A2 with a 30K btu fuel fired heater, I would have to hold it in the start position several minutes (seemed like a long time) before it would take off. It would stink and smoke before she would fire, once it started to sound like a little jet, I would then put it in run. The colder it is outside, the longer it took in the start position to warm up.

 

[gimpyrobb]

Sounds about right to me.

 

[m-35tom]

if it has not been used in years the fuel is likely sticking things up. use lacquer thinner. do NOT ever use air pressure you will destroy the regulator.

 

[74M35A2]

All good points. Thanks team. Have been reading the manual so now ready to try your suggestions as well as check components.

 

[cranetruck]

if it has not been used in years the fuel is likely sticking things up. use lacquer thinner. do NOT ever use air pressure you will destroy the regulator.

Be careful when selecting a solvent, tiny O-rings and rubber membrane(s) may swell and not recover. Gasoline is probably best, just be fully aware of the fire hazard.
If the control valve is not "clicking", the control circuitry may be at fault. I may have one, removed from a 60K BTU unit...will check in the morning.

 

[cranetruck]

This is what I have for the 60K BTU heater, PM me if interested.

 

[Wildchild467]

I helped 74M35A2 work on this heater also. I have the smaller (I think the 30,000 BTU) unit in the back of my M109A3 of which I put a new wick in it, so I have a little bit of experience with them. He originally sent it back to Stewart Warner to have them troubleshoot it but they said it needed a whole rebuild. The unit looks near new and does not look like it has had many hours on it. that bring said, I would think it would fire off. Now that SW looked at it, we found a wire that was not connected to the terminal block. After seeing that, it makes me want to double check all the wiring to make sure everything is correct before 74M35A2 and I move forward troubleshooting it. I dont think anything is really wrong with something being miswired, but its not too bad to check and it would drive us nuts if we are chasing around components when the real problem is something not being wired correctly.

Bjorn,

Do you think that heater on the "fuel metering block assembly" is needed? I noticed there is some other piece of circuit right next to the heater on the "fuel metering assembly" that looks like it might be the thermostat for it, is that correct? I looked in the manual briefly and that little electronic module was not covered. It is not that complicated, so I cant see where it would be anything more than a thermostat for the heater. Thank you for your help with this heater. 74M35A2 and I appreciate it.

 

[74M35A2]

Be patient, I am going throught it all now. I didn't want to be an expert on this, but it is heading that way. The fuel metering block has a heating element with a snap type thermostatic switch in series with it. The thermostat is supposed to open at 70F. It looks like that may not be happening, or that cavity is not filling with fuel.

The fuel solenoid was clicking correctly before I sent it to SW. I think just the flame detection switch was not adjusted correctly. But now that it came back from SW, the fuel solenoid is not clicking, and a wire was off of the terminal block. Wire re-installed, and still no solenoid clicking. Solenoid resistance measured 180 ohms, I need to compare that against spec and see if the pulse generator is sending the signal to open the solenoid next. Flame switch works correctly, and over-temp switch ohmed out ok. Blower motor works. We just need to get the fuel injection working, adjust the flame switch, and then riding in the 925A2 should never be cold again!

Dam it, I didn't want to know all about these heaters! The gentleman I bought it from is a scholar though. He heard I was having trouble with it, and he sent me all new replacement components. So, it is really just a matter of finding our what is not working, and replacing it.

Thanks all.

 

[cranetruck]

The parts shown in my previous post are for the older, simpler model, which has two solenoids, one for "HI" and one for "LO", so they won't be of much help. Sorry about that.
The newer single solenoid units modulate the on/off and thus control the fuel flow.
You may want to put an ohmmeter to the coil wires and check for continuity or isolate it and apply 24 vdc and hear it operate...

 

[74M35A2]

Got the fuel injection solenoid working. SW had 2 leads reversed on the electronics board. I didn't see detailed connection about this in the TM, but I reversed 2 that could easily be swapped mistakenly, and it atarted clicking, double rate on high, so I think that part is ok now.

Should be ready to test now. Stay tuned.

 

[Wildchild467]

Were you going to use this heater for the cab or the cargo bed? I forget. I'm anxious to see this thing in action. opcorn:

 

[Storm 51]

Do you guys only play with the newer heaters? And how do you define "new"?

Does anyone know about or have experience with the old SW 978 series heaters? Or maybe even a few parts?

Storm 51

 

[cranetruck]

With "new", I refer to anything after ca 1975. Ha Ha

I may have a manual for the 978 somewhere, I'll get back to you.

 

[cranetruck]

This is the Feb 2010 MVM issue article on the heaters, not the new and not the 1940's, but should help understand the operation, since it's similar for all.
If you find patent numbers on the labels like 2133103, 2150650 and 2191174 on the 978 units, do a patent search for very good info.

View attachment 2010 0201 mvm feb 2010 issue, Fuel burning heater article.pdf

 

[gimpyrobb]

The gentleman I bought it from is a scholar though. He heard I was having trouble with it, and he sent me all new replacement components.

I heard he was "not right" in the head!

 

[Wildchild467]

I heard he was "not right" in the head!

A couple injectors short of a multifuel!

 

[Wildchild467]

Will dyed diesel or dyed kerosene hurt these heaters? I know wick style lamps and heaters will not like the dyed fuel and it shortens wick life. Will that do the same to these units? I am just thinking if the vaporizer clogs up or goes bad, where do you get another? I would hate to keep working on these things. Although the heater in the back of my M109 does not currently work. I need to check it out and fix it. I think the wick burned up again. The wick for that 30,000 BTU unit was 1/8" fiberglass. Is it the same wick for the 60,000 BTU unit we are talking about in this thread? I would think it would be but thought I would ask.

 

[phil2968]

"Multifuel", the heater was made to burn anything the truck was built to burn. It all comes from the same tank.