This is a jump-off from my thread on cooling system troubleshooting, as it looks like it's a condenser fan issue that is causing the overheat.

Fan motor was replaced a couple of years ago, so don't think that is the issue (but haven't tested it yet; see below for my plan to do so).

I tested voltage on both sides of the 100A fuse that is supposedly for the condenser fan (F4 in the fuse box in the engine compartment) and got 12.7v with engine off and 13.8 with engine running.

Pulled relay (R4 n the fuse box in the engine compartment). See pics below. Tested and it seems to be good: 3-5 pins show 0.3ohms when 12V is applied across pins 1-2, otherwise pins 3-5 are open.

Though not the typical 85-87 diagram, it appears that pins 1-2 are the energizer/control and pins 3-5 are the power.

Tested voltage and resistance at the blades/pins

Pin 1: AC off: 13.7V AC on: 13.7V open
Pin 2: AC off: 0.7V AC on: 5.7V open
Pin3: AC off: 0V AC on: 0V 14ohms
Pin5: AC off: 0V AC on: 0V open

Based on this it appears that the energizer circuit has voltage-current -- albeit the 0.7-5.7v on Pin 2 (normally to ground?) seems weird. There is no voltage-current on either pin 3 or 5 of the power circuit, though the 14ohms on pin 3 seems consistent with what would be expected for the windings on a motor.

I am going to test the condenser motor here next by putting 12v DC on pin 3 and see if it spins (normally, I would do it at the motor connector itself, but I have that foam-ish OEM grill guard, which makes it a pain to remove the grill to get to the condenser fan motor connector).

As there was voltage on both sides of the fuse, I assume that the fuse is before and not after the relay on the power circuit?

Does this mean I have an open circuit somewhere in the fuse box between the fuse and pin 5 the relay? I am guessing there is a wiring harness/backplane on the underside of the engine compartment fuse box, perhaps with a bus bar or similar that provide 12v for the power circuits for the relays?

Am I on the right track here?

Does anyone have any advice?

 

Does the fan spin by hand ?? If not it’s seized

can’t your just jump the relay and see if they come on ? Do this while truck and ac is running

or just put 12 v right to fan You can you the accessory socket s13 as it’s fused in case something is wrong with fan.

 

Thanks for the reply.

Normally, I would just jumper the relay socket with a paperclip, as I do this all the time to troubleshoot AC compressor issues.

Problem here is that there is no power (voltage) on pin/blade5, which is what I am assuming the power source for the fan controlled by the relay energizer (pins 1 and 2).

It would be great if someone (hint, hint) could confirm that pin/blade 5 (or maybe 3, but I think 3 goes to the motor) should indeed show 12v If someone confirms that, then I pretty much know that the problem lies somewhere in the 3-4 inches in the fuse box between the 100A fuse (F4) and Pin5 (or Pin3) in the condenser fan relay socket.

BTW, I am assuming that R4 is the correct relay as it is the only one with the picture of a fan on it.

 

i have 12 bolts between 1- 5 pins
jumping them does nothing

 

I turned on ac. Fan doesn’t come on at first but if you let it idle it comes on. Not sure if it’s pressure or temperature.
I know if the truck goes above 220 or so that fan does come on.

go on disco web and look at the rave

 

So removed the grill -- I have a stupid OEM foam brush guard on it which makes the removal of the grill a 30 minute job (instead of 30 seconds) -- and it appears that some mud dawbers (wasps) built a rock-hard mud nest in there that kept the fan from spinning, so guessing I burned it up. It hasn't sat for more than a week or two, so those little buggers must have worked fast.

However, with the grill off and the fan out, I was able to confirm that the Pin3-to-Fan connection is good, as is the fan-to-ground. This means that Pin5 is definitely supposed to be the power source from the relay socket.

I am ordering a new motor (VDO PM1928). I replaced once already a couple of years ago, so no big deal.

Bigger problem is in the engine fuse box.

While I have 12V on one side of the 100A fuse in the condenser fan relay circuit, on the other side of that fuse I have no continuity to (presumably) Pin5 in the relay socket.

I am guessing that there is a wiring backplane on the underside of the fuse box, and that the wiring route from the fuse mount to the relay socket Pin5 burned up as the motor kept drawing current while trying to break free of the mud nest.

Has anyone ever worked on the engine compartment fuse box and can tell me how to remove it and what exactly I will find on the underside in terms of a bus bar and other wiring?

 

Here's pic of what happens to the brush assembly, stator and armature when the condenser fan is stuck in place by a muddawber's nest.

My really smart electrical friend broke it down as follows:

As the condenser circuit (ECU controlling pin2 to ground via pin1 and pin5 delivering current thru pin3 to the motor) delivered up to 100A of current (the size of the fuse in the circuit), the motor brush(es) stuck at that point, not being cooled by the movement of air from rotation within the motor housing, melted down and one of them actually crossed two windings on the armature, causing even more current to flow and the armature assembly to swell because of the heat, so even if the mud nest had been discovered and removed, the damage to both the brushes and armature had been done pretty quickly.

As the motor continued to accept more and more current, eventually the (I am assuming) 16-18 gauge wiring in the fuse box backplane from the 100A fuse on the fusebox busbar to Pin5 in the condenser relay socket failed well before the fuse would've (still doesn't make sense why they put 100A fuse to protect a circuit with wiring that could only accept 30-50A of current; one of the mysteries of how the English mind works that we Americans will never understand; maybe they just had extra 100A fuses in the bin at the factory?)

Moral of story. If your D2 sits idle for a while, peer thru your grill to see if any wasps have decided to set up house on the nice warm condenser inside the fan shroud.

While I wait for a new motor to come in (btw, it is a VDO PM9128), I am going to start a new thread on the engine compartment fuse box and if/how to repair it after an overcurrent event like this.