JWAC air heaters

[John]

After a couple of days of real cold weather this past October in Rhode Island, with ice on the deck of the boat, tried to start engine (270 HP 6BTA JWAC CPL 2956) and noticed the voltage cycling for the grid heaters wasn’t happening. Engine very hard to start, and when it finally did, a lot of white smoke poured out of exhaust. Engine finally settled down and warmed up. OK. Something going on with the grid heater. Check grid solenoid and ECM, and I see that the short cable jumping 2 posts (referred to as “contactors 1 and 2” in wiring schematic) at the ECM are rusted and the rubber post caps have melted over the nuts. OK. Bad contact and rusted nuts at the posts caused this problem. Attempt to remove nuts and clean up contacts. Power cable and nut on right contactor removed. Nut on left contactor (circled in photo) is firmly frozen to the post and the post is spinning with the nut = post broke, this component is toast. Fortunately, I have a block coolant heater on engine (Fleetguard 3825424). I plugged it in, and on subsequent cold starts, engine fires right up. I hauled the boat for the Winter November 6th, so now I’ve got to resolve this issue.

Based on research, the grid heater solenoids and ECM’s are subject to problems and failures. Tony’s recommendation is to remove the solenoids and ECM and wire a manual switch to grid heater. Yet another solution is to disable the grid heater (pull fuse) and install a Wolverine oil pan heater. My coolant heater serves that purpose. I should point out that I seldom need air heaters to start the engine. I’m aware of the drain on battery and alternator (I have a beefed up 160 amp Delco). Until really cold weather shows up, I would always start the engine without waiting for the voltage cycling to end. Just run the RPM’s up a bit (800 rpm) for a few minutes to keep alternator current strong enough to feed the air heater. Schematic shows a magnetic pickup measuring RPM that’s part of the ECM heater system, and a higher RPM will shutdown heaters (I think).

My plan is to pull power cable from starter to contactor, and to remove the ECM plate and contactors. I will replace that with a console ON/OFF switch to control the heater element, and cycle the switch for cold weather starts.

So, here’s my issue and question… Where the heck are the air heater elements on a JWAC 6BTA engine ? There are no grid-type heaters around the turbo. Cummins manual representation shows turbocharged air to JWAC manifold which sucks air into intake valves. There’s a thermistor, a component of the air heating system, measuring intake manifold temperature, plugged into base of JWAC. Schematic shows 2 heater elements with power coming from the ECM contactors (solenoids).

The attached picture shows my attempt to disconnect wires from solenoid and ECM. Post on right is power cable from terminal on starter. Post on left is the frozen nut and broken post. In the picture, the 2 larger red wires above the contactor posts should be source of power to heater elements. Wire harnesses and access on this engine make it difficult to trace. On the other side of the engine (port) there’s a thin 2-wire connector with label tape on wires. Wire label tapes around the engine are difficult to read from heat and age, with some blank and others barely legible. Red wire labeled “Preheat amp”, and black wire labeled “Heater module power”, as best I can determine.

So, again, where are the air heater elements, and is it as simple as to wire a fused on/off switch to the heater elements?

Topic

[John]

Corey,

I assume Tony’s “this may help” was a reference to Tony’s Tips. I was able to find a couple of articles on air heaters. More than likely he’s referencing the “5-minute Twist Timer or Momentary Switch” schematic and the picture of a contactor mounted to the JWAC.

For now, I’m going to remove all the components and wiring from the ECM and contactors. I’ll mount a switch on my console to activate the heater during startup. Do you guys sell the magnetic switch contactor for this fix?

[Corey Schmidt]

Tony Athens wrote:

This may help.

Tony, are you missing the attachment?

[Tony Athens]

Picture of Air Heater Grid

This may help.

[Justin Riege]

I just looked at that article that Rob posted. I have installed a few wolverine heaters and they are a snap and work really well. I would strongly recommend that route if possible.

If you do do the switch thing. It sounds like you have some corroded components wiring etc.

To me it seems the best thing would be to remove all the control apparatus for the air heater just get rid of it. Especially since its corroded and causing some problems.

Once you gut all the old stuff get a good contactor (mag switch) that can handle some decent amps. Grab power from a good source for the contactor, and send power to coil of the contactor with a timer switch that is fed from the ignition switch so the key has to be on to run the heater. Between the timer and the key switch, and a little caution, you can avoid leaving the thing on too long in the wrong conditions draining your battery. Its simple but it works. Only do this if you aren’t the forgetful type.

How many amps does that heater draw Rob?

[Justin Riege]

As usual Rob be me to it. Hehe,

Here is a pic of one we have in the warehouse. The arrows pointing to the positive posts.

[Rob Schepis]

John wrote:

Where the heck are the air heater elements on a JWAC 6BTA engine ?

Nice pics. Your second picture captures it at the top of the pic. My attached pic should help. And here’s a link as to wiring to a control switch.

https://www.sbmar.com/articles/electrical-instrumentation/dealing-with-the-cummins-marine-air-heater-circuit/

[Author]

Replies