2005 Ford E-350 5.4



With Multi-Function Selector Switch on Max A/C a purple Wire becomes energized with 12 volts.

wire goes through low and high pressure switches which are both currently jumped with a piece of wire for troubleshooting purposes.

wire with 12 volts completes its journey and then goes to PCM pin 3.



PCM pin 4 is NOT providing a ground to pink/yellow wire which goes to pin 2 of the ac control relay, which should cause relay to click and join a fused 12 volt wire with a wire that goes down to the ac compressor clutch.
I have verified continuity of all these wires, pins, and connectors.



Is there perhaps some other data that is making the ecm unhappy? some folks have suggested a power steering pressure sensor which will cause the pcm to cut off the ac compressor if making a harsh turn at low speed but my vehicle doesnt have one.



do i need a high end obd scan tool?

mine is a basic actron, it does show live data but probably nothing for a/c demand info.



if i bypass this, but still make sure to keep the low and high pressure switches involved for safety reasons and not be a barbarian hacker, then does cutting the pcm out of the equation cause any drawbacks? for instance does the pcm automatically raise the idle to compensate for the ac compressor being on? (i'd really like to fix it the right way though)

 

Just as a note, you have the PCM pins backwards in your post. Pin 4 is the input from the pressure switches, pin 3 is the output to energize the clutch relay.

Yes, you need a more capable scan tool or equivalent. Most folks use Forscan and an OBDII adapter. There are a number of PCM-detected faults that will disable the A/C clutch. The service manual simply says to diagnose and repair all faults flagged by the PCM before doing anything else when working with a non-functional A/C system.

 

you are correct, i double checked that in the book as well as my notes.......

something very strange is how for pin 4 it says "a/c clutch relay switched output". when in fact this is the 12v demand signal that is an input to the pcm. it originates at the dash multifunction switch, when set to max a/c, it sends 12v through a purple wire, which goes through both low and high pressure sensors, and then goes directly to the pcm pin 4. the color is right, black and yellow. theres not a whole lot of other black and yellow wires in there. NOW, there are multiple pages for pcm connectors, some of which are for a diesel, which i do not have, and those are obvious, this page appears to be the right one, i hope it is.... but hand over handing the wires, probing them, toning them, and checking their continuity doesnt lie!

 

Again, follow the manual's explicit instructions which I already provided. You can waste a LOT of time (and money) by ignoring that instruction.

 

so be it, i will hookup my scan tool and look for faults. not all faults will trigger a check engine light, but may still come up, and if it doesnt pick them up, i will need to invest in a more advanced scan tool.

you said.....
"There are a number of PCM-detected faults that will disable the A/C clutch"
what is that number? and what are they?
okay, this picture may be what you are referring to.....






powertrain control/emmissions diagnosis manual is the only one i dont have.

 

You have "The Book" right in front of you. Follow it and do not skip steps - they are there for a reason. Do not wander off into the weeds on your own, that's where the ticks and chiggers are and they'll eat you alive.

 

I have a question as I am experiencing the same issue described above on my 2006 e250 5.4l. My background is air conditioning and refrigeration on commercial equipment. My relay has constant 12v positive to one side of the coil but no ground. The will sometimes engage But it will cause the relay to chatter. The relay will be on off on off 10-20 times in a 2 -3 second time frame. I have checked system pressures and bypassed the pressure switches to rule out the idea of a faulty pressure switch. I put a scan tool on the system and checked the pcm command for air conditioning. The command said allowed but still no ground sent from the pcm. I also noticed that when the ac was turned to the on position “WAC” would also turn to the on position. I am thinking the pcm is faulty but I don’t want to replace it unless I can confirm a diagnosis.
is there anything else I can check in order to rule out other issues aside from the pcm being faulty.
here are some photos as reference from the scan.



Ac clutch allowed

Wac on, it was in the off position when ac was not requested.


Scan tool showing dtc faults could this be another sign of a failing pcm?

 

PID ACCS is the series input from the pressure switches. Yours show that input is "True" or "On" meaning the PCM C175b-4 is receiving a valid request to turn on the system.

The PID WAC is the PCM's command to turn on the clutch relay. It also shows as "True" or "On" meaning the PCM *should* be providing a ground to the PCM pin (C175b-3) that is connected to the low side of the relay's coil (pin 2) causing it to energize.

I would postulate that either the PCM's output driver for the WAC signal is failing/faulty or there is an electrical circuit concern (poor connection, high resistance, etc) in the portion between the physical pin on the PCM and the corresponding pin on the relay socket. If you have an appropriated backprobe adapter and can reach that pin, that would give you a better idea of the exact fault. Don't overlook a visual exam of the PCM and harness connectors, there might be something obvious once opened up.

 

Why in the world is the book calling this pin 4 "a/c clutch relay switched output" when i know for a fact it is the 12v series input from the pressure switches??? The wire color is right. The description is NOT. The a/c clutch relay switched output is on the relay itself and is a gray/white wire that goes to the a/c compressor clutch.




Backprobing? Good luck! I use wire piercing probes. You turn the **** and a needle pokes a hole thru the insulation of a wire and the multimeter leads hook right to it. To ensure the connection to the pin is intact i use a thin piece of wire hooked up to an alligator clip and touch the metal contact inside the tiny hole of the female connector where the male pin on the pcm would normally fit into. I have great continuity at all connections.
Scan tool does not show any p1460, p1464, or p1469 codes.
I need a scanner like he has.
I may have to get something that can do the job cheap, or pay someone to hook their tool up to my rig. i am looking into forscan, there are also some amazon scanners scotty kilmer recommends that can do it.

 

You'd have to ask the author. ***** happens... You just have to learn to interpret the crap so it makes sense "in the real world". They didn't ask me for my input at the time, I'm just explaining it in a way that's more understandable.

Many of the forum members use Forscan, it's basically a clone of the Ford IDS system and is a common denominator among users. You can use whatever is capable. As noted, the new participant in the thread is using a Snap-On, an extremely capable (yeah, but costly) tool. You can get the needed capability with Forscan for under $40 if you have a Windows laptop.

 

i just got lucky with the fact that I did some ac work at someone’s house that I saw had one and asked to use it and they let me … that thing is to expensive for me haha. But I checked continuity from the relay to the pin everything is looking good I did manage to get a p1464 code on my little scanner but after looking into it, it just says it was from running the test with the ac on. I’m looking into trying to get a new pcm… I may hold off for a bit but everything has pretty much lead back to it unfortunately…

 

i've also noticed in the flowcharts where it says to test for voltage at the ac compressor clutch connector it shows a view of the connector and the right pin to probe (one is switched voltage that comes from the relay, one is grounded at all times, it says the wire is yellow/black when it is NOT! It is gray/white and its not just faded, i cracked open the harness and hand over handed it, that sombitch is gray/white!

AutoDad on youtube loves forscan, he shows how to install it and use it. Id have to get a doohicky that plugs into the diagnostic port. Better imo to get the fishing pole and be set!

Yeah that snapon scanner is about $5k.
Thanks for the info about "accs" and "wac" those are possibly going to be handy to know

 

What specific pinpoint tests are you seeing that? That wire, according to the schematics and wiring diagram, is supposed to be GY-WT. In looking through pinpoint tests "C", I don't see any reference to any other color of wire in my version of the WSM or EVTM.

 

Typo City up in this book.

Just to be clear on terminology....
a/c cycling switch c130 means "low pressure switch"

and pressure cutoff switch c1078 means "high pressure switch"?

i know it has to be cause i traced it all out, the terminology is weird.
and this pcm is being a bitch.

i am a heartbeat away from splicing the high pressure switch output wire to the hot side of the relay coil and running a ground to the ground pin of the relay coil, that way when i flip the dash switch to max ac it clicks the coil on, keeps the safety low and hi switches in place, powers up the clutch.....and.....whammo.....bobs your uncle!

the only thing i am uncertain about is if the compressor will make the idle sag, because i dont doubt the pcm increases the idle when its running. how much it will lug the engine i dont know, that may be my next experiment

 

Worse than that. it appears you have the diagnostic routine for the 2004 and prior model year E-series in that book. Wonder if it was an early printing version...

Yes, both those are correct according to the diagrams I have.

That's been done before.

BTW, it would also work in any other climate control position except OFF, VENT, and FLOOR.