Tricky Air Conditioner

[kingpolaris]

Stamp is he by chance related to King Brad? I always love these type that come on and brag about having a BS in something and do want to listen to the people they came on the forum seeking advice from.

i've got some great advise from Skauber, already ordered the bluetooth OBD2 reader. this is obviously too techy for some and i apologize. i'm really just trying to fix this piece of crap in my driveway. low refrigerant pressure at this point is beating a dead horse. i only referred to my degree because it is the simplest way to give my back ground without having to state how many vehicles I've worked on or how many years i have as a tech or whatever (I'm not better or smarter than anyone here, thats why I'm asking the questions).

I've spent too many years on pirate4x4 so my skin is pretty thick, zero ***** given here on what you think. like i said before just looking for advise, thanks.

so...what's your thoughts on the pcm? i have no idea on how to check it.

 

[stamp11127]

Google "r134a chart" and look at the blue acpro chart. For 105 ambient your low range is 50-55 and high is 330-335. With the compressor not running the low and high sides will stabilize. That is probably what you are seeing now - static pressure. What is this reading and the temp you are taking it at? Once the compressor engages the low side will start sucking in the refrigerant due to the lower pressure compared to tank pressure when recharging. The only time you need to heat the tank is when the outside of the tank has been icing up. When that happens the refrigerant is no longer changing to vapor inside the tank. Really doubt you will have that problem in the desert heat.

Turn a/c on, check for power on the low press plug. If you have power here then check for power at the compressor plug. If you have power at this plug then take a resistance reading of the compressor clutch coil.

These systems operate similar to home a/c - just use different refrig and are smaller. The t/s steps still apply.

PCM - when you jump the a/c clutch relay it energizes the coil. See the wiring diagram. Takes the pcm out of the equation as long as the coil is getting power. If it works after jumping the relay then I would take a look at the other switches in the system. Play it safe right now and don't probe the pcm connectors.

 

[Skauber]

The PCM rarely goes bad, but it can happen. If you suspect a bad coil driver, swap the offending coil over to a different cylinder and see if the problem stays put, or moves with the coil. That's a simple first step to rule out PCM and wiring.

For the AC, if there's something the PCM is not seeing, like it never gets the signal from the low pressure switch due to an issue with wiring or similar, it will not engage the compressor. Before suspecting bad PCM, you have to verify that the PCM is seeing all the signals it needs to see, and check if the PCM is commanding the compressor on or not. A hardware issue in the PCM would still see the PCM commanding the AC on, but the output driver will not respond accordingly. A software issue in the PCM where the PCM simply just has to be reprogrammed (with a dealer specific Ford scan tool) will show the PCM receiving everything it needs to command AC to on, but it just doesn't do it.

 

[kingpolaris]

The PCM rarely goes bad, but it can happen. If you suspect a bad coil driver, swap the offending coil over to a different cylinder and see if the problem stays put, or moves with the coil. That's a simple first step to rule out PCM and wiring.

For the AC, if there's something the PCM is not seeing, like it never gets the signal from the low pressure switch due to an issue with wiring or similar, it will not engage the compressor. Before suspecting bad PCM, you have to verify that the PCM is seeing all the signals it needs to see, and check if the PCM is commanding the compressor on or not. A hardware issue in the PCM would still see the PCM commanding the AC on, but the output driver will not respond accordingly. A software issue in the PCM where the PCM simply just has to be reprogrammed (with a dealer specific Ford scan tool) will show the PCM receiving everything it needs to command AC to on, but it just doesn't do it.

the coil is good, i swapped coils and the problem stays with #6 no matter what coil pack i put in it's place. im still waiting on a better scanner but i did notice that i resistance reading back to the pcm is way higher than any of the other coils. i will find more info on that tomorrow when my buddy stops by with his ford scanner. im glad to know there is a possibility of it being able to be reprogrammed.

after looking at the diagram provided by stamp i believe i either have a bad chassis ground at the pcm or like you said the pcm is not seeing a sensor and it is opening the ground circuit.

ill let you know what i find tomorrow, thanks!

 

[Bedrck47]

It always makes me wonder why those that seem to know it all always have to ask for help and then tell you they don't want to listen. You can give all the prints and advice you want but again if its not what they want to hear then all you have accomplished is a waste of your time and knowledge. Then they think the one that says more on the lines of what they think is the best one to turn to or they have to get their Ford mechanic to look at the problem Makes you wonder why they didn't go to him in the first place.

Just my opinion

 

[Skauber]

Since the P0356 stays when moving the coil, then the issue is either a wiring issue or connector issue (most likely) or a bad PCM coil driver. If it's the latter, you will probably have to replace the PCM, or have it repaired. You can repair it yourself if you know how to. If it's simply a bad output driver, it might not be too difficult to replace that component if you can source it from ebay or something, but it is required that you have good skills in soldering and have good equipment of it, and know how to work with SMD components.

Depends on your budget, you can get a new/used PCM on ebay for around 100 bucks, but you'll have to get it programmed to the vehicle and your keys

 

[kingpolaris]

Just a quick update. Found a company on ebay that repaired the PCM. Thank you SIA Electronics (highly recommended)! The local repair shop wanted nearly $2k to replace the PCM with an OEM part. I paid about $160 for the repairs - took about a week to get the PCM back but was plug and play. The expedition passed smog and seems to running a lot better. AC is working great! Lesson learned - don't expect the AC to work if you lost a coil driver for one of the cylinders in the PCM. Thanks Skauber for the assist on this difficult project.

 

[Skauber]

Great to know! I guess the PCM has some sort of software thing that disables the AC if it detects a dead cylinder to conserve power or something.

 

[Daraksta]

Thank you for posting this. P0356 just took out my ac as well. Shaking pretty bad too but I made it home. Figured ac was related to the miss, both happened at the same time intermittently.