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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 verified continuity of all these wires, connectors, and pins.
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). i know in a rare overheating condition the pcm could also cut off the ac, this i dont care about ever occurring and i certainly dont see anything like that going on here right now......
2005 Ford E-350 5.4 Liter 5R110W Automatic
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.
You'd want a scan tool that can dig deep enough into the commands the ECM should be sending to the A/C compressor. You'll also want an EVTM for your specific year like this one on eBay: 2005 E-Series EVTM
Be advised those are very year specific especially for 2005's and later as the electrical circuits changed quite a bit from 2004 and earlier due the addition the CanBus network including "fly by wire" throttle body etc. The free software FORScan is worth investigating if you have a laptop. Do be advised there the ELM interface from the DLC to the laptop makes a big differerence, I opted for one of the better but slightly more expensive than the ultra cheap ones out there, to wit: TCD ELM327
Do be advised that outfit Total Car Diagnostics has a special running on their software that's worth investigating: TCD TOAD
Your A/C system pressures are what exactly?
You have the high and low side switches jumpered for what reason exactly?
There are several parameters that must be met before the processor will allow A/C clutch operation
System pressure is the main one
Cooling fan if equipped must function
Vehicle must not be overheated
You'd want a scan tool that can dig deep enough into the commands the ECM should be sending to the A/C compressor. You'll also want an EVTM for your specific year like this one on eBay: 2005 E-Series EVTM
Be advised those are very year specific especially for 2005's and later as the electrical circuits changed quite a bit from 2004 and earlier due the addition the CanBus network including "fly by wire" throttle body etc.
i have that book. it is worth its weight in gold. the only book i do not have is the "powertrain control and emissions diagnosis" manual.
Your A/C system pressures are what exactly?
You have the high and low side switches jumpered for what reason exactly?
There are several parameters that must be met before the processor will allow A/C clutch operation
System pressure is the main one
Cooling fan if equipped must function
Vehicle must not be overheated
low pressure switch is normally open. it becomes closed when the pressure exceeds a specified psi.
high pressure switch is normally closed. it becomes open when the pressure exceeds a specified psi.
for each, one wire goes in and one goes out. they are wired in series with each other. very basic on/off switch that has a plunger inside. plucking the connector and inserting a "u" shaped piece of wire eliminates them as a possible cause of the problem by sending 12v directly to a pin on the ecu (which is what they do anyway)
unless there is another sensor somewhere (i.e. the evaporator) i dont get why the pcm is not happy. i can charge the ststem up to full capacity if it makes you happy, but i have a leak near my condenser, and im not wasting all that money on refrigerant or polluting the ozone until i fix the leak, (and this electrical problem)
i have read that an overheating condition (or what the pcm sees as an overheating condition) will cut the circuit off, however the data for that looks okay.
I hooked my van up to a scanner with the same issue. My ac climate control is operational and the pcm is reading that the ac clutch is allowed. I also noticed when the ac was powered on “wac” also turned on..? Could this be part of the issue?
