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So my AIH (Air Intake Heater) system had a total meltdown all on it's own and I found some interesting stuff.
The root cause, was the busbar between the two halves of the grid heater. It runs along the bottom and 17 years, 25k miles, plus dry desert conditions (Kuwait, El-Paso, Houston till 2021) was too much for the insulators that keep it from shorting to the housing and they shrunk leaving the busbar loose on it's bolts:
This caused the connection to the front grid to overheat and smoked the insulator - acrid electrical smoke pouring out from behind the cab after lunch (heater was not being commanded so we have another mystery - why is the heater running on my lunch run when it's 60 degrees out?) So the solenoid is suspect.......
Had to open up the solenoid - can't trust that anymore. This was new - genuine CAT last summer:
So here's what happened - the heater efficiency dropped off due to the poor connection at the busbar. This ran up the solenoid duty cycle till it overheated and the plunger spring that breaks the contact with the terminal studs and the plunger disc lost it's spring temper and shrunk. This caused the disc to sit right down next to the terminal studs and any bouncing of the vehicle was pulling the plunger down and turning on the grid heater. Insidious failure mode that could have easily resulted in a FIRE. Luckily I keep my engine clean and free of oil or this would have certainly been a different and much more tragic story. The design of the solenoid and where it's located on the C7 is BAD. First if the plunger spring fails in this way the solenoid would be better oriented upside down so the plunger is pulled away from the contacts by gravity when it's de-energized. Also rain runs right off the back of the cab directly onto this solenoid continually bathing in it a waterfall. This has been a significant enough problem that the military did introduce a relocation kit for this solenoid on the A1P2 trucks.
In addition - the fusible link is of very poor design for where it's located off the LBCD stud. The braided weave over the link is clearly not watertight and this thing looks worse for the wear. One end was obviously taking the brunt of the moisture. Going to replace this with something else along with the solenoid - maybe solid state
1980 called and wants it's cheap "artisanal" fuse back.
The root cause, was the busbar between the two halves of the grid heater. It runs along the bottom and 17 years, 25k miles, plus dry desert conditions (Kuwait, El-Paso, Houston till 2021) was too much for the insulators that keep it from shorting to the housing and they shrunk leaving the busbar loose on it's bolts:
This caused the connection to the front grid to overheat and smoked the insulator - acrid electrical smoke pouring out from behind the cab after lunch (heater was not being commanded so we have another mystery - why is the heater running on my lunch run when it's 60 degrees out?) So the solenoid is suspect.......
Had to open up the solenoid - can't trust that anymore. This was new - genuine CAT last summer:
So here's what happened - the heater efficiency dropped off due to the poor connection at the busbar. This ran up the solenoid duty cycle till it overheated and the plunger spring that breaks the contact with the terminal studs and the plunger disc lost it's spring temper and shrunk. This caused the disc to sit right down next to the terminal studs and any bouncing of the vehicle was pulling the plunger down and turning on the grid heater. Insidious failure mode that could have easily resulted in a FIRE. Luckily I keep my engine clean and free of oil or this would have certainly been a different and much more tragic story. The design of the solenoid and where it's located on the C7 is BAD. First if the plunger spring fails in this way the solenoid would be better oriented upside down so the plunger is pulled away from the contacts by gravity when it's de-energized. Also rain runs right off the back of the cab directly onto this solenoid continually bathing in it a waterfall. This has been a significant enough problem that the military did introduce a relocation kit for this solenoid on the A1P2 trucks.
In addition - the fusible link is of very poor design for where it's located off the LBCD stud. The braided weave over the link is clearly not watertight and this thing looks worse for the wear. One end was obviously taking the brunt of the moisture. Going to replace this with something else along with the solenoid - maybe solid state
1980 called and wants it's cheap "artisanal" fuse back.
