Heater - A/C Blower dead at ALL speeds...

Hey all, I have been messing with this since last weekend and I have run out of ideas. Hopefully, one of you electric gurus can shed some insight and help me out. I have no blower and (likely as a result, the a/c button on the control panel is unresponsive - no light and obviously, no a/c) Here's a list of things I have found / done:

(The truck is a 2012 4.0 DC MT 4x4 btw)

1- Verified blower operation by quickly jumping the Heater Relay - all good downstream.
2- Replaced Heater Relay - no change
3- Removed and inspected the resistor and connector - no obvious signs of burning etc
4- Confirmed blower dial ("D") resistance values are within limits per FSM
5- Checked and swapped IG1 #2 fuse and heater blower fuses - no change
6- Confirmed 12v at location "A" (Ig on, fuse removed)
7- Found zero volts at location "B" (fuse installed)
8- Measured resistance between "A" and "B" at 145 ohms... seems odd.
9- Conductor "C" leads to another relay which I believe it also energizes.

If I am understanding the schematic correctly, that IG 1 #2 fuse should be energized with the ignition on and then grounded when the speed selector switch moves to any position beyond Off, completing the circuit and activating the relay and starting the blower.

So that 145 ohm value seems to be the problem (I think) apparently, enough resistance to not energize the relay (?) I pulled the kick panel and unplugged the connector DC (I think, the outer side) and no sign of anything funky there. I have not made it to the back side of the JB yet...

Another possibility is the fuse/relay block under the hood I suppose but, I thought I'd post here before I get too crazy, quite possibly sniffing up the wrong tree - (I'm hoping ; )

If anyone has any insight on what my next move should be, I would seriously like to hear it. At least this happened at a not so bad time of year, temp wise, it could be a lot worse - TIA

-Jeff

 

That 145 ohms between A and B is suspect. Maybe the terminals down in the fuse spot are crispy?

 

Not a crispy or otherwise suspect connection found so far but there are several more locations that are possibilities. Strange though, this is the low power side of the relay, not like a blower motor connector etc

 

Right.. control side..

Jump a wire from A to B and see if everything returns to normal. If it does then you just narrowed down the problem.

Or worst case, you just leave the jumped wire (around the resistance) in there and just roll like that

 

Yep, thought of that but would need access to the underbelly of the fuse/relay block under the hood. Was hoping I was overlooking something else, that sounds like a pita. I suppose 10a ignition could come from many sources, so the power end is easier. maybe I could snake a temp wire in from the outside just to see

 

Hook the ohm meter back up and do the wiggle test along the harness and fuse box. Get your hands on stuff and flex it around, see if the resistance drops or jumps around

 

makes sense, thx. I already made a long jumper with a fuse terminal and a wire soldered to it (and checked it's res. ; ) I'll do that tomorrow morning.

 

This for an '05 but in your year it might be more...

 

Did you verify?

 

Found the problem. Rodent attacked the harness below the clutch MC. It was on the side facing the brake MC so it was not obvious until I poked around a bit. I think I can get to it to splice in a few inches of wire for a repair.

New problem will be keeping this from happening again. Keeping the hood up at night may not be enough - GRRRR

Thanks for your input everyone.

 

WOW! That's a new one. Usually they go after the knock sensor wires which are much more difficult/expensive to repair.