%#@%$_$!@_* So, I'm reading another of Sean's PDFs. This one describes the general functionality of the AC system. On the first page, the first thing it describes are all the system components. The dual pressure switch is not in the list, but that AC Cycling Switch is, and the arrow points at what I know as the dual pressure switch. OK, that makes sense, I thought the connectors looked the same.

But then, it has sections describing each of those components, and lo and behold, there is the dual pressure switch AND the AC Cycling Switch. I'm now thinking they are the same component, but it's called a Cycling Switch on gassers and a Dual Function Pressure Switch on diesels.

So, continuing down the procedures, it tells me to check the Dual Function Pressure switch by jumpering from the red/yellow to a wire they describe as TN/LG, which I assume is Tan/Light Green?. But, my truck doesn't have that wire. They have mentioned the grn/or wire, so that can't be it, and I have the black ground wire shown in the diagrams, so that leaves the black/yellow wire in my connector to be this TN/LG, except it's in a different pin location than the procedures diagram. The pin in that procedure is the one with my black ground wire on my connector.

So, I jumper between those. The procedure says to put the key in the Start position. Is that the same as ON? Or do they mean to actually start the engine? Either way, I've tried it both, and the compressor never engages. In that case, the procedures say to test that TN/LG circuit for resistance.

That involves pulling the PCM connector it describes as C1381a - how can I tell which of the three that is? I know which one has the transmission harness, so it's not that one. IIRC, another goes to the engine/injectors, etc. Not sure what the third does, but maybe it's the instrument panel, and includes the AC circuit?

And, how do I test resistance with this power probe - again, the dang thing didn't come with instructions? And, how do I know which pin in the PCM connector is Pin 8, the other end of that TN/LG wire? And, what are the chances that pin is the right one, since so much else in these procedures is flaky for my truck? If it doesn't ohm out, how do I know I even have the right pin?

Maybe I should just jump ahead and swap in that other PCM, just to see if that fixes it.

 

Well, after swapping in the other PCM there was no change to the compressor, so I decided to take the bus to a local shop to diagnose the problem. However, they can't get to it until next week, so I still have a few days to tinker with it.

Until now, I've followed the Ford diagnostic specs, which led me test the continuity of the circuit from the Pressure Switch connector to the PCM harness end. I got a 0.0ohm reading, which seemed suspicious, but IDK, and the procedures said to swap the PCM, Which I did with no change to the compressor; so now, I'm taking a different approach. Starting from the compressor field coil, I'm tracing backwards to find where it loses voltage (there's none at the coil now with the key on, AC on, and pressure switch jumpered).

The coil connector is just two wires. One goes to ground, and my power probe confirms that ground is good. The second wire is supposed to supply voltage from the AC Clutch Relay. I'm at that Relay now.

My probe confirms that the Relay does have voltage coming to it from the Battery Junction Box. On the wiring diagram, I see a power circuit connecting through the Relay to a control signal coming from the PCM. That causes a second circuit on the relay's other two pins to close, allowing voltage coming from a second Junction Box fuse to power the compressor coil.

I believe the voltage I detected was the diagram's Red circuit to the PCM, but I'll confirm today. It appears that other, Grey/White circuit would also register voltage at its relay pin, and I think I did record that, but I'll confirm. I've also confirmed that all the Junction Box fuses are operating.

Assuming I do have both of those voltages coming into the relay, then one or both of the two internal relay circuits aren't closing so that the voltage does not make it out of the relay to the compressor coil. I know, kindergartner stuff, but I gotta plod along like this. Sorry...

First question: can I use my power probe to apply 12v to the Grey/White circuit at the relay socket going to the field coil to confirm that the circuit is intact and, if so, that the coil does engage? Shouldn't I hear the clutch trying to engage, even if it's locked up?

If I do hear the clutch clicking, then - obviously, I need to confirm that the relay is good. Assuming that it is (I've swapped it around with identical relays), I'd next need to look at the PCM control circuit, right? To confirm that it's intact and being controlled by the PCM.

How do I test that? I assume I can do a continuity test on the wire in the harness again, but is there a way to ground it with the power probe and hear the clutch engage?

If that works, if effecting that PCM control signal triggers the clutch, I'm hosed, right? I've already swapped PCMs. The truck fired right off with the replacement. What else would be making the PCM control signal to the relay not function, except a bad PCM?


Recap of my questions:

1. Confirm that my probe should detect voltage at the socket for that grey/white wire coming to the relay from the Junction Box.
2. Can I use my power probe to apply 12v to the relay socket of the grey/white wire that leaves the relay and goes to the coil, to confirm that the circuit is good and that the coil does engage when it does receive voltage? Shouldn't I hear the compressor click when I do that?
3. Please confirm that even if my compressor was frozen, it would still record voltage at the connector and, maybe, I'd still hear it try to engage if I sent voltage to that connector (I don't record or hear anything now).
4. How can I check whether the PCM is grounding(?) that control signal to the relay?
5. Any other suggestions why voltage is not making it to the coil?

The field coil and relay are in the lower right corner of this wiring diagram Jack provided.

FYI - everything about the front blower motor, including the blend door and Function Switch operation, appears to work fine now after I replaced the #13 fuse and blower motor. However, I am assuming the Violet circuit going to the "AC Clutch Switch" (wherever and whatever that is) is good because the Pressure Switch has voltage. And by jumpering that voltage across the connector to the socket going to the PCM, I am assuming that eliminates the low/high pressure or switch being the electrical issue.

That switch's circuit to the PCM is the one the diagnostic procedures led me to test for continuity, which I did and got 0.0V, which seemed suspicious, IDK, but was under the 5ohms required. If that was a valid reading, the Ford diagnostics told me to next replace the PCM, which I did and nothing happened. The procedures don't tell you what to do after than, lol.

I don't know which, if any, of the other sensors that feed the PCM AC-related data could prevent the PCM from grounding that control signal to the AC Clutch Relay so that voltage doesn't make it to the coil. Again, any suggestions appreciated.

Finally, remember that there is another separate, aftermarket AC system on this truck, and it also does not seem to work. I have no idea where or whether the electronics of the two systems connect, if at all. I suspect (for no reason, I'm ignorant) that there is no connection of the aftermarket system to the truck's fan clutch, temp sensors, etc., or its PCM logic. I am hopeful that the aftermarket system is essentially self-contained and only connects to the bus for base 12v power and fan belt drive of its compressor mounted on the driver's side of the engine. It appears the mfg modified the Aux Fan switch to serve as a PowerON/LowFan, MedFan, and HiFan switch, instead of the three-function Fan switch shown in the OEM wiring diagrams, but I can't see the compressor clutch or hear it engaging from inside the cab when switched on to confirm the ON/OFF functionality.. It's fan does blow at three speeds though, so the switch is delivering power back there. It may simply have a freon leak and if I can find the pressure switch to jumper, or whatever it takes to get it to accept refrigerant, I could begin that repair process.

 

LOL, don't mind me. These are like My Diary entries. "There was a cute relay in my electronics class today."

Ok, so I got 12v at two pins on the relay socket, but the writing is too small to read which ones those are. Still, I applied 12v to the other two pins, and I could clearly hear the compressor clicking. So, I'm on the right relay and I know my compressor coil is working. So that leaves a bad relay, a bad PCM control circuit, or the PCM isn't doing whatever it's supposed to do to that control circuit (ground it, I believe).

Why would the PCM not ground that control? Pressure switch, but I jumpered it. Bad circuit from the pressure switch? That's the one I tested and got the 0.0 ohms resistance reading. Fan clutch? Cylinder head temps? ECT? The engine isn't even running at this point, and I read all those PIDs just fine when it is through OBDII. But, that's all the inputs into the PCM according to the AC Wiring diagrams.

I still see that mysterious "AC Clutch Switch" between the Dash Function Selector and the Pressure Switch in the diagrams, and can't tell what it's switching.

So, maybe, the next step is to jumper the AC Clutch Relay - give power to that pin that's making the clutch click now, to see if the clutch will engage and the compressor will turn with the engine running? Or, can I do that with the power probe, with the relay out and the engine running? If the compressor turns, I'll check the refrigerant pressure.

 

Muttering some more...jumpered the relay and the compressor engaged, started the engine and it stayed engaged. No freon. Not sure why jumpering the pressure switch didn't get to this point, but anyway...dumped a couple of cans of freon in and its cooling just fine now.

I haven't tried it yet with the relay back in yet. I get too hot outside this time of day. It does seem like the front blower fan wires are too hot. The PO had the connectors cut off and the two wires spliced together, so I had to cut the connector off my new fan motor to wire it the same way. Now, the wires were warm to the touch at the fan motor, while it was running full speed inside. Maybe that's what burned up the last fan?

 

So, to update these ramblings, because you can't claim the Bonehead crown without documentation...

I'd gotten excited earlier this week, thinking that I understood how something electrical worked. I remember this kid in the 4th grade, used to put jigsaw puzzles together the wrong way, forcing pieces together - he'd get excited too. I can only say that I get less excited these days, nothing but a pilot light on that burner - but, dang, if I don't risk a flicker on that wiring diagram, only to have it bite my wick off again. It's like I was looking at one of those autostereogram hidden pictures for hours and finally the image of the red race car magically appears...only to find out there's really a silver F35 fighter plane image.

Hey, but I did locate the AC Clutch Relay all on my own. It wasn't where any of the pics said it was. I went down the obvious rabbit hole - like the pic-makers connive - of assuming the diagrams are flipped over since the junction box is on the other side of the engine compartment on diesels. BwaHaHa. So, I guess I learned how to not read wiring diagrams, which I expect to serve me well in the future.

I haven't a clue how any of this works, what the wiring diagrams say, why the compressor engages when I jump the relay and not when I jump the pressure switch. Why do 6-month olds splash in the bath? What any of that has to do with the starter not engaging with the key. I'll never know; but I know it's blowing cold air right now - so I haven't screwed it up too much yet. It even worked with all the relays and switches plugged back in as they should be, as if it never didn't work.

Or, for at least for a couple of miles. Until the freon leaks out again. If it's still there today. It was 30/175 and cruising when I turned it off yesterday..

But to find out how this turns out, you'll have to wait for the next episode of....The Bonehead on Ice Show, starring Phlegmy Fleming!!!

Next week features the return of one of the show's more popular guest hosts, Tonya Hardswing! With her pry bar and Bonehead's spindly ankles, they skate through the location and repair of that freon leak, and the whole crew motors across the Mojave in 70 degree luxury for the big party scene at Ludlow Cafe. Here's the teaser, from the Helsinki show with Bonehead famously riffing his Air Ratchet.


After that, we invite Axel Rose onstage to pirouette with Phlegmy and Bonehead to the...Rear AC!! Riff City!!!

 

Well, I didn't mess with the freon leak today. Started it up and the pressure was still 30, but now 200 on the other side, so I guess the leak isn't just oozing out while it sits here.

Found the service manual for my Carrier rear AC, and like I hoped, it is independent of the OEM system. And the dash control does exactly what I figured - turn once to turn on the AC and low fan, then two more times for med and hi fan.

So, that's all working - the fan comes on in all three speeds. But, the compressor doesn't engage, so I expect it's out of freon as well. The low and high valves are in the lines under the bus, and the low pressure switch is in the evaporator box hanging from the ceiling in the back of the bus, and of course, the compressor is up front. At each one of those components, I can't monitor either of the other two, lol.

But, I found the relay in the Junction Box that powers the rear AC, it's in the spot that the OEM diagram has assigned to the rear trailer battery charge relay. And, it's a different relay than all the others - would it make sense that the aftermarket mfg would have needed the relay to act differently after modifying that socket to run the rear AC, such that he needed a relay that connected different pins, etc.?

I'm thinking this AC is no different that the OEM system in its basic function, such that if it's low on freon I should be able to, somehow, bypass that pressure switch and get the clutch to engage so I can pump some freon in. However, the pressure switch doesn't have a removeable connector; it's wires are hard-wired to the harness. Here's pics - it's the green device. See how it's two wires go into those white plastic connectors that don't seem to come apart. Have anyone worked with connectors like that - can I pull the pink fitting out of the white rectangle?

Or, do you think there's another way to get the compressor to engage so I can pump freon?

 

So have you gotten is figured out?

I may have some other models on DVD sitting around here somewhere.
What year and model am I looking for?

 

Thanks, Sean. Definitely been a learning experience from which I haven't learned much, lol. I doubt I have an electrical issue at all. When I bought it last December and immediately had the starter quit engaging by the key, and knowing it had some other minor electrical issues, when the ACs both quit working around the same time, I kinda assumed it was an electrical issue too. Then, when I couldn't get the front compressor to engage by jumping the pressure switch, and wasn't getting voltage at the field coil, I again assumed that confirmed that it was an electrical issue - and down that rabbit hole I went, not having a clue what I was doing.

I don't know why jumping the relay made the clutch engage, when the pressure switch didn't, but once I got some refrigerant into it, it all works fine. So, I got a leak somewhere in that system. I'll see how long it takes to leak out - it's just too hot here in Houston to work on it right now, and I'm not getting back on the road for another month. By then, I'll only have 6 weeks or so before I don't need that AC again. Maybe it'll hold refrigerant that long and I can fix it once it cools down.

However, I still got the rear AC to figure out - and I'd really like to have it working. This front AC won't cool the whole bus. But, I'm pretty sure it's a refrigerant leak as well. One thing I did learn that I didn't know - just by hooking the gauges up, I can tell if it's out of refrigerant by whether the two gauges both show a temp close to ambient. If so, it should have enough refrigerant to engage the compressor, from what I read. This rear AC has no pressure at all on either gauge. So, I expect it's got a leak too.

Not sure what causes leaks - maybe because this truck sat up for a few months before being auctioned? IDK. Since the rear AC is completely empty, I wouldn't mind checking for leaks - maybe replace the Schrader valves just because? But, I haven't figured out how to get the clutch on that compressor to engage. I'm thinking I can jump across the two wires going to the low pressure switch, but I don't want to burn anything up. Or, maybe I jump the relay? I did find the service manual for it, but I didn't see that info anywhere.

Have you ever seen wires spliced using that white connector in the pic? I can't tell if that pink fitting pulls out. Again, don't want to break anything. If they do, it would be easy to jump those.

 

well, dang, the manual is too big to attach. Let me see if I can pull some relevant pages from it.

 

here's a diagram of the ac system and the service section of the manual. It doesn't say how to make the clutch engage, grrrr.

 

Replacing the Schrader valves is always a good place to start for leaks.

Get your hands on a good UV lamp for looking for the glowing spots
in the system.

I found one that works really well
https://www.ebay.com/itm/38426810954...AAAOSwS1hgmRM6

BTW it is not for cleaning or killing germs. At one point they were claiming it did that at the peek
of all the panic. You know they type trying to make money off of freaked out people.

Anyway it works well for finding where the UV dye has leaked out. This also works for coolant and oil.

 

Thanks, Sean. I still got to figure out how to get refrigerant in the rear AC. Here's maybe an easy question - I'm trying to buy one of the Schrader valve tools that don't loose any refrigerant, and I've learned that there are different types of Schrader valves. From looking at several products, it seems the most popular valves are sized !/4" and 5/16". Does anyone know what size our valves are in the AC?

Here's a link to one of the tools on Ebay. I've watched video on how they work, but still don't quit see how one tool with only one valve connection can work on two different sized valves.

https://www.ebay.com/itm/15450572840...Cclp%3A2334524

 

I don't have an answer for that one. Not a refrigeration guy.

 

You and me both. I ordered it and hopefully it works. Can't look at this again until next week. Gotta go put a roof on my dad's house.