How to Add Automatic Temperature Control (ATC) to a Manual Temperature Control Truck

skuppy069 said:

I got a new truck yesterday with dual zone and it has the humidity sensor on the windshield.
My guess is 0/RT is right on the money with the humidity sensor causing the problem.

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Did you buy a new truck?

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Yeah I did .

skuppy069 said:

Yeah I did .

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Congratulations!

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Thanks .

I just thought of something. If someone were to disconnect the humidity sensor on a dual zone 14 or newer 1500 I wonder if the A/C compressor would default to on like it does on our trucks? I have a friend with a 1500 Laramie. He lives out of town but next time I see him I might see if he'll let me unplug it to see what happens.

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Ricks Ram said:

I just thought of something. If someone were to disconnect the humidity sensor on a dual zone 14 or newer 1500 I wonder if the A/C compressor would default to on like it does on our trucks? I have a friend with a 1500 Laramie. He lives out of town but next time I see him I might see if he'll let me unplug it to see what happens.

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I was actually just about to try that on my 18 Ram Laramie ...

Edit:
Stock Dual Zone ATC w/humidity sensor (85°day)
- Manual (MTC) mode: AC button shuts compressor clutch on/off as expected
- Auto (ATC) mode: compressor stays on continuously.
Tried adjusting temp all the way up/down ... No Change = ac clutch always engaged.

Stock Dual Zone ATC w/humidity sensor DISCONNECTED (85°day)
- Manual (MTC) mode: AC button DOESN'T shut compressor clutch on/off
- Auto (ATC) mode: compressor stays on continuously.
Tried adjusting temp all the way up ... No Change = ac clutch always engaged.







M² Mods.

Mpgrimm2 said:

I was actually just about to try that...

Just need to verify something first.

M² Mods.

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Thanks! That would definitely answer some questions.

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Previous post edited.

M² Mods.

Is the harness already in the truck. Ive scanned mine for codes and its not throwing a code for that sensor so it must not be setup yet with the ATC upgrade.

WilliamS said:

Is the harness already in the truck. Ive scanned mine for codes and its not throwing a code for that sensor so it must not be setup yet with the ATC upgrade.

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No the harness is not there. I think @Ricks Ram has one on order with the humidity sensor. One he gets it it’s going to be trial and error to see if 1) it actually needs to be on the windshield to work correctly and 2) to see if it has to be enabled in the bcm to tell the truck that it has a humidity sensor. That’s most likely why you are not getting a code is because the truck doesn’t know it is suppose to have a humidity sensor.


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Yes I ordered the harness,sensor and the cover. I was talking to Mr Grimm and we were thinking I might not even need the to mount it on the windshield. As long as I am able to add the code and the truck picks it up I can pretty much mount it wherever I want. It won't necessarily work exactly as was is it designed because it's not going to detect humidity on the windshield but I don't really care if it does that or not. I've never had an issue with my truck fogging up in the past before I added the ATC and I've never had a sensor before I just want to be able to turn my system on and off manually. I haven't had a chance to look for the code yet because I've been super busy but I am a little bit concerned I won't even be able to find it especially because my truck is a 2014 and for some reason a lot of the codes don't show up on the AE tool for the 2014 trucks.

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Ricks Ram said:

Yes I ordered the harness,sensor and the cover. I was talking to Mr Grimm and we were thinking I might not even need the to mount it on the windshield. As long as I am able to add the code and the truck picks it up I can pretty much mount it wherever I want. It won't necessarily work exactly as was is it designed because it's not going to detect humidity on the windshield but I don't really care if it does that or not. I've never had an issue with my truck fogging up in the past before I added the ATC and I've never had a sensor before I just want to be able to turn my system on and off manually. I haven't had a chance to look for the code yet because I've been super busy but I am a little bit concerned I won't even be able to find it especially because my truck is a 2014 and for some reason a lot of the codes don't show up on the AE tool for the 2014 trucks.

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Where are you located? I think I saw that option when I was digging around in the bcm activating the fog lights.

loveracing1988 said:

Where are you located? I think I saw that option when I was digging around in the bcm activating the fog lights.

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I'm in CA. I have the AE tool. I've just been too busy to actually go in and see if I can find the code. I'm assuming there should be a setting in the Lin configuration but I'm not sure if there's any other settings.

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Ricks Ram said:

I'm in CA. I have the AE tool. I've just been too busy to actually go in and see if I can find the code. I'm assuming there should be a setting in the Lin configuration but I'm not sure if there's any other settings.

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Well that's a far drive... It seems like the app I have does give the option to enable it. I am really tempted to do this mod now. If m2 mods happened to offer just the harness from the cabin air temp sensor to the ac module and the humidity sensor to wherever it plugs into it would probably be a hit too since it's such a cheap mod.

M2 Mods will most likley come up with something if we are able to get the codes figured out. They're very good about staying in top of things and trying to make sure that they provide harnesses for most of this stuff. If I didn't love the ATC control so much I would probably just put the truck back to manual but I've really gotten spoiled to it. Nathan and I are going to try to get to it Monday or Tuesday and see if they AE tool is capable of activating the code. Of course we won't know if the codes correctly set until we actually connect the sensor and see if it works.

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loveracing1988 said:

Well that's a far drive... It seems like the app I have does give the option to enable it. I am really tempted to do this mod now. If m2 mods happened to offer just the harness from the cabin air temp sensor to the ac module and the humidity sensor to wherever it plugs into it would probably be a hit too since it's such a cheap mod.

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Isn't your truck a 2500?
If so it is unaffected by the potential humidity sensor issue and the current ATC Sensor add-on harness works without issue because the 2500/3500 have the fixed displacement HVAC compressor (vs variable in the 14+ 1500's).


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Is there anywhere I a wiring diagram that shows the humidity sensor? I've looked at 3 different model years and I can't find it on any of them.

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loveracing1988 said:

Is there anywhere I a wiring diagram that shows the humidity sensor? I've looked at 3 different model years and I can't find it on any of them.

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Just for others since it was in a pm...

But it's in the Lin Bus diagram.

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Mpgrimm2 said:

Isn't your truck a 2500?
If so it is unaffected by the potential humidity sensor issue and the current ATC Sensor add-on harness works without issue because the 2500/3500 have the fixed displacement HVAC compressor (vs variable in the 14+ 1500's).


M² Mods.

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Just wanted to confirm what DeereGuy and Mpgrimm posted concerning the 2500 / 3500's.

I have a 2017 2500 Cummins Regular Cab that came from the factory with the 7 speed fan but only MTC. ATC is not an option in 2500/3500 regular cabs. I added ATC using DeereGuy's harness and the OBD Genie. I just checked the function of the A/C compressor. When in manual mode I can shut the A/C compressor ON or OFF with the dash button. So my truck acts the same as DeereGuy posted previously. Hope this helps.................

OK StecoD and I finally got the Humidity Sensor,Mirror Harness and cover today. We also got the pinned jumper wire to bring the ignition on run power to the harness that the mirror harness plugs into (thanks Deer Guy) I spliced into the number two pin going to the heater control module which is ignition on run positive and then ran the pinned wire into the correct pin in the connector that hooks to the mirror harness. To save time I just removed my rearview mirror and unplugged it from the existing harness and then laid it on the dashboard and plugged in the new harness with the humidity sensor. I'm very happy to report that the system now seems to function normally. I can turn the A/C on and off with the button and no matter what temperature I set the temp at the compressor does not come back on until I hit the A/C button again and I can just run the truck on vent if I chose to. I was completely prepared to put in the codes tomorrow but to my surprise the truck doesn't seem to need them to function normally. I've been in contact with M2 mods throughout this whole thing. They have been very helpful and I'm sure a conversion harness is in the works for them to get out to everybody to correct this problem. Also thanks to OO/RT for his guidance to try to help figure this out. I posted a few pictures but I'm sure M2mods will have excellent instructions with the conversion harness they build as usual. Picture one shows where I spiced into ignition on run wire. The second picture shows where I inserted the pinned wire into the back of the harness that plugs into the mirror harness. I had already covered it with protective tape. The third picture shows the whole mess on my dashboard when I was testing it. I also included one last picture showing the ignition on run wire in the connector that plugs into the heater control module.

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