"In-Duct Electric Heater" - Dodge Cummins Diesel Forum
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post #1 of 57 (permalink) Old 11-18-2019, 09:03 AM Thread Starter
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"In-Duct Electric Heater"

Hi guys,

I read the press release from FCA on the 2019 RAM HD trucks. It states the diesel trucks have an "In-duct electric heater" which helps supply heat prior to the engine warming up.

It does not specify if it is standard equipment on all diesels or all trim levels. However, in the build and price feature of the website, I do not see it as an option anywhere.

Prior to this, only Ford offered a supplemental electric cabin heater, available since 2010. The heater used two 50A circuits up through 2016, and for 2017 to current was upgraded to three 50A circuits. This was optional equipment on the Ford, and required dual alternators because of the immense current draw. I had both the 100A and 150A versions on my previous Ford diesels and found it to provide lukewarm heat at best.

My 2018 Cummins warmed up exceptionally quickly and well with the exhaust brake switched on.

So I'm curious about this feature - if its standard, and how it works. I see nothing in the owner's manual fuse locations page showing such a heater, and my truck has a single 220A alternator. So call me suspicious.


2019 RAM 3500 Crew 4x4 Cummins H.O.
2018 RAM 3500 Crew 4x4 6.7L DRW Manual Trans - previous
2017 Ford F-250 Crew 4x4 6.7L Powerstroke
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post #2 of 57 (permalink) Old 11-18-2019, 09:59 AM
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I believe itís standard in the diesels. The relays for them are 1,2,&3 and the fuses are 4,5,&6 in the AUX PDC fuse box.
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post #3 of 57 (permalink) Old 11-18-2019, 10:04 AM
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believe the aux heater is standard on the 19 models. i know mine gets warm pretty quick. not as fast
as when i have it plugged in, but you can tell there's something going on

'19 2500 t'man
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post #4 of 57 (permalink) Old 11-18-2019, 10:30 AM
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Standard in 19 with CTD option

Jimmy07, thanks for the diagram.
The 2019's (haven't checked the 20's) has an auxiliary supplemental cabin heater as standard with the Cummins engine option, regardless of trim.

I have been testing it to see the effectiveness. Here is what I have observed. On a cold morning, below 35F, within about 2 minutes after start, when I place my hand over the windscreen defrost vent, I can feel very warm air. Everywhere else blows a small amount of cold air. After another minute I can feel warm/hot air out of the side window defrost vents. The floor vents and face vents now blow cool air. When the engine temps get to about 125F, hot air is available at all vents, and the entire cab is already warm. This is on my Laramie trim model, Auto climate on and set to 74F drivers, 73F pass. I had the same results last week when temps at startup were single digits.

So it seems like the heater kicks in to the windshield defrost vents first, then transitions to the side defrosters, until the engine can start to step up give heat around the 125F mark.

On a side note, my 2007 Mercedes ML diesel has the same heater set up, but the heater pushes hot air to EVERY vent and has the smaller cabin completely warm by the time I get to my first subdivision stop sign. The Ecodiesel Jeeps and RAM 1500 has also had this feature for years.
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post #5 of 57 (permalink) Old 11-18-2019, 10:45 AM Thread Starter
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It does seem to be working on mine, because stone cold I have warm air pretty quickly. What is the electrical draw on this? I know for European diesels, fuel-burning heaters are very common. Pure electric powered heaters are rare simply because of the required electricity.

The 150-amp Ford circuit produced 1200watts of heat, which is the equivalent of a hair dryer. That isn't going to heat your cabin very quickly. So I'm surprised that RAM has an electrical heater with only a standard 220A alternator. The grid heater, DEF heater, auxiliary switches, etc, etc could easily overdraw what the alternator can produce. With the Fords, dual alternators were required as I mentioned, producing 357A total.

I know a lot of older European vehicles used fuel burning heaters; I'm surprised your 2007 Mercedes would have the alternator capability back then to power an effective heater. Seems like in 2007 a 150A alternator was near the top of the game. Maybe they used a more efficient heater? I never was all that impressed with the output on the Ford electric heater, because at best you would get lukewarm heat at low fan speed. Even moderate fan speed would cause the air to become cold. The Ford heater was installed just downstream of the heater core. Maybe the RAM duct heater works better with less power because the heat element is closer to the exit? I dunno.

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post #6 of 57 (permalink) Old 11-18-2019, 11:30 AM
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The technology has improved The in cab heaters are known as PTC heaters and are ceramic. Very little power needed, works fine on 12V system, and they get to an exact temp and hold that based on the demand placed on the heater, by reducing current. Several automakers have been using this for years, especially the Toyota hybrids, as they need heat as you drive away until the engine starts.

I was skeptical like you, after the issues I had with the 220A alt on my last 13 RAM during cold weather and watching the grid heat cycle. So for the 19, I ordered with dual 220 alt's. I had lots of files and was actually building a pair of these PTC heaters to warm my 2013, but gave up and ordered the 19 when I saw the press release with standard ceramic aux PTC heat. Here is a link to a company that makes PTC heaters. I had a link to the OEM builder for VW/Mercedes/Jeep/RAM, but that page can't be found anymore.

The ML has a very sophisticated electrical system that was designed by engineers that got A+ in every class they took since birth. Starting with their placing the battery inside the cabin. The system uses the same ceramic PTC heater as others, not fuel fed, and that vehicle fortunately has never skipped a beat since it was delivered.

2019 RAM 2500 Laramie CTD, Crew Cab, 4X4 all options except rear air susp, Black Forest Green Pearl.
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post #7 of 57 (permalink) Old 11-18-2019, 11:43 AM Thread Starter
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Thanks for the info. I'm surprised Ford (apparently) didn't use this technology on their new 2017 Super Duty.

I had a 220A alternator on my 2018 RAM and it was fine. One thing that drives me nuts is the headlights dimming and fan slowing down when the grid heater cycles. Ford and Chevy diesel trucks use glow plugs and don't do this.

My buddy had a 2016 Cummins with the dual 220 alternators, and his lights still dimmed when the grid heater cycled, so I guess you just can't get away from it.

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post #8 of 57 (permalink) Old 11-18-2019, 11:49 AM
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The 19's dual alt's and LED headlights lights solved it for me. No dimming, no blower speed change, nada.
Wish I didn't have to fork out the cash I did to get here though.

And yup, wish RAM/Cummins would use the ceramic glow plugs that everyone else is using. Would solve 85% of their electrical issues, and wait to start time would be miliseconds not several seconds.

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post #9 of 57 (permalink) Old 11-18-2019, 12:07 PM Thread Starter
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Hmm. The LEDs do use less, but total headlight draw is only 110 watts on low.

Nice truck you've got there!

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post #10 of 57 (permalink) Old 12-04-2019, 03:47 PM Thread Starter
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So I finally have solid info on the "In-Duct" heater, straight from the workshop manual from FCA.

The heater is located in the heater box downstream of the heater core. It consists of three 400W resistors, which translates to 100 amps at 12 volts.

Operation is automatic, based upon the following conditions being met:
-Engine must be running at 700RPM or greater
-Outside temp is below 68F
-Coolant temp is below 158F
-Battery voltage must not fall below 12.6

This supplemental heater can be had on vehicles with automatic or manual climate controls. However, the workshop manual lists it as an option rather than standard equipment. Check your fuses / relays under the hood. The manual calls it a "Positive Temperature Coefficient" heater, or PTC.

To conclude, this is actually less powerful than the supplemental heater in the current Ford diesels (150A in those) and designed extremely similarly.

One advantage of the RAM system is that it can activate 1, 2, or all 3 resistors depending upon load and temperature.

The system activates immediately upon engine startup...but I would suspect it might drop out for the first few minutes when the grid heater runs. I've had my voltage screen up, and each time the grid heater lights, my voltage has dropped as low as 11.7 momentarily.

Anyway, I'm happy RAM has finally introduced this useful feature. For some reason this 2019 seems to warm up a little less well than my 2018 Cummins.
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post #11 of 57 (permalink) Old 12-04-2019, 11:13 PM
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Excellent find. I have been searching for this info for a while. Many many thanks!!

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post #12 of 57 (permalink) Old 12-05-2019, 08:33 AM Thread Starter
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dgiturbo, what is the lowest your battery voltage drops to right after a cold startup? I'm curious how much the dual alternators help. I have the single 220 and as I mentioned, when the manifold heater cycles, the volts drop to as low as 11.7. I'm curious if yours remain above 12.6 volts.

As I mentioned in the past, to get the Ford supplemental heater, it automatically bumped you to dual alternators because the draw was so high.

As an aside, in reading more in the manual it talks about how the batteries have a state-of-charge monitor and have the ability to "load shed" under high demand...namely, they can automatically drop things like heated seats and steering wheel, heated rear window defroster and mirrors, and drop blower speed to a bare minimum. However, you should see a "battery saver" message in the cluster. I've yet to see that, but of course the batteries are brand new.

2019 RAM 3500 Crew 4x4 Cummins H.O.
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