TechTalk8160K Service Bulletin/Repair Instructions

3/23/2021 Re: Alternator Overcharging with A/C switch On onl... - DTNA Solutions
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> Re: Alternator Overcharging with A/C switch On onl...
({D) Jim_McGee

Knuckle Buster
02-22-2021 08:59 AM
Alternator Overcharging with A/C switch On only
Curious if anyone has come across on a New Cascadia when the A/C is turned on the

alternator spikes to 17 volts and it only happens when the center button for the A/C is turned

on as soonas it is shut off it goes back to normal. Looking at different schematics they only

appear to come in close contact in modules in the VPDM, | thought maybe the A/C Compressor

was Causing it but with it unplugged it still does it. There does not appear to be any damage to

wiring and the remote sensor fuse is not blown, sadly | do not have a test HVAC controller head

to try, not sure if that could cause this or not. Any assistance would be useful because | have

never come across this issue before and | have contacted Freightliner and they were at aloss

too.
Truck Info
2019 New Cascadia

VIN KD3711
Mileage 341,187
Labels:
( Cascadia ) (Electronics | Controls | Configuration | Communication | and Diagnostics )
( EngineTransmission Cooling | and HVAC ) (Freightliner ) ( Power! Electrical | Harnesses | and Wiring »)
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GES
B Steve_Reppard
Piston Head

02-22-2021 11:27 AM
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3/23/2021 Re: Alternator Overcharging with A/C switch On onl... - DTNA Solutions
| would check voltage at alternator remote sense connections and make sure nothing is

spiking or dropping out. Have you checked wiring that runs in front of oil pan- this is acommon

chaffing point.
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Ome
& Jesse_Gutierrez

Solutions Pro

02-24-2021 07:17 PM
| have also had the wiring chafe along the air compressor as well
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(o| O Kudos }
({D) Jim_McGee

- Knuckle Buster
02-25-2021 10:58 AM
Checked all the usual chaffing points and found no damage to wiring, continued and removed

ground wire to alternator from the starter and checked it to make sure that ground was good

and now with the A/C on it tops out at 14.9v with the A/C on. This is making me wonder if there

was just a ground issue due to the spray they put on the electrical connections from the

factory. | installed a jumper between the plug of the voltage sense harness to the alternator to

monitor voltage with A/C on & off, on it is at 13.8v and off at 13.5v. Currently working with

Freightliner to try and get some answers but they seem as baffled as | am on this one.
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3/23/2021 Re: Alternator Overcharging with A/C switch On onl... - DTNA Solutions

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(o| 3Kudos }
£6 Wy Talbert_Simonia

( = @ King Pin

02-25-2021 02:30 PM
Please keep us informed on this. But | think you got it with the possible ground issue.
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(0 2 Kudos }
@ VJesse_Gutierrez

yy’ Solutions Pro

02-27-2021 12:49 PM
Ok thinking about it now similar issues we had one P4 Cascadia with clock springs etc working

not working due to bad grounds
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(0 OKudos }
({D) Jim_McGee

Knuckle Buster
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3/23/2021 Re: Alternator Overcharging with A/C switch On onl... - DTNA Solutions
03-03-2021 06:38 PM
| found the issue and it was a surprise, | went back over the wiring harness for the voltage

sense wire and noticed a section that was swelled but there was no external damage to the

harness. | cut the tape off the harness thinking someone had repaired this and found the wire

corroded through and it had started to cause another wire to lose insulation on it. The only

thing | can think of is that the wire might have been damaged when the harness was built and

over time the moisture got into it and caused it to corrode and eventually break. Once |

repaired these wires with the system started to charge at 14.2v with the A/C on or off. The

wires | found are close to the bracket under the MCM that goes into the harness that goes to

the 21 pin connector. | appreciate the help on this all of you it did help me eliminate certain

items.
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[me
ie Jesse_Gutierrez

Solutions Pro

03-03-2021 07:00 PM
Nice , sometimes as a quick troubleshooting step | will run a quick jumper from my load to

source / etc and see if everything works if not then | know it’s hardware or software related at

that point and can go after those issues
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(o| OKudos }
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3/23/2021 Re: Alternator Overcharging with A/C switch On onl... - DTNA Solutions

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