ATA 29-11-22 ACMP INOP IN AUTO MODE

Working on a 767-200 pilot reported that the #2 ACMP is INOP while in auto mode but working properly when switched to on. 

First thing I did was just a normal ops check right away when switched to auto the pressure light comes on and we never get any pressure. When switched to ON full pressure and no issues using the hydraulics.

First step was to check out a few of the relays and time delay on the auto side and see if we are getting any power. The relays and time delays are all in the P33 in the MEC so easy trouble shooting all in one place. 

 
 
 


So had an odd findings everywhere that im expecting to see 28v im seeing 1v-3v so way way low. Just to be sure of myself i replaced k126 and k128 relays with new since already available in my hand. No help and still getting the low readings at both relays and time delay module. So smelled like high resistance, actually if you reference the fuel section on this forum you will see 767 will fuel cutoff switch having high ohm reading. I worked on that job with Mark a few years back and thats what lead me to try the switch right away. 

Found that the switch reads extremely high ohms sometimes open while in the auto position and .5 ohms while in the ON position.

 

I then decided to jump pins 8-12 so bypass the switch and see if the pump would operate as normal just to fully verify the switch as the problem. Luckily while jumped everything is working as it is supposed to.

 




Considering this to be isolated parts on order and hopefully MEL cleared soon!
 

Damn good troubleshooting. I’m also assuming the FIM never came out on this problem?

Thanks Mark! Nope FIM never suggests the panel itself and jumping the pins just my idea to double confirm the finding. FiM just general wiring issue from P33 to panel.