Volvo VNL 670 bunk a/c and heat quit working

You might need new batteries

 

Check the wires make sure you are getting all proper grounds and powers what year is the truck did all the fuses have power mainly fuse f1 thru f7 those are the LECM fuses If one does not have power the LECM will act up they usually go on with the battery protection mode everytime I do a starter I have to jump the fuses in order for everything to work. Let me know what year your truck is and what kind of engine you have also check underneath the bunk behind the driver seat right behind the side signal its hidden away make sure you check all the connections for corrosion let me know what turns up and if you need any more help

 

to get it working again you have to take the control unit out and unplug it for a few seconds then plug in it will reboot. It is stuck in protective mode. Also run a ground wire from the cab to the battery this stopped all my cab electrical probelms.

 

i have the same year,engine, & model truck it should work have done it many times

 

2oo5 isx 500 with Zf auto. I have had the same problem. There are six grounds on this "thing". Two starter to batteries, one at each end of the four. The main ground. One from the frame to the batteries. One from the engine to the frame and the ground that goes from the harness to the engine by the starter. I had to change the batteries to a higher cca. I been taking the gang plugs apart and cleaning corrosion and putting dielectric grease in every plug. Even inside the cab - it's pathetic I own a Hino that was 16 yrs old and had 1.8m k on it before I was forced to stop driving it because the frame broke and I never had wiring issues like this thing does.
Disconnecting the batteries also resets the "computers".