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Discussion Starter · #1 · (Edited)
Just in case anyone else runs across this issue.

My wife was driving, she claims she heard something (perhaps coincidence), then the AC starts blowing hot. After shut down when she restarts the car there is a check engine light - AC still not working. I think the AC belt (which is original with 80k miles on it) has probably snapped. It didn't.

I pull the codes and find this mess . . . which should have been a bigger hint than it was. The car was running great . . . then all of a sudden the codes say it is falling apart. The picture is just some of the codes that popped . . . there were 10 or so.

https://photos.app.goo.gl/oxQ8DtEv4VSY1g4Q6

After contemplating just ordering an entire new AC system (since it's 13+ years old, and all original), I find a video about removing shims to temporarily patch an AC system (which I'm fond of, because my wife is touchy without her car). https://www.youtube.com/watch?v=x6084NqhbeE

Ignoring common sense, I don't test the circuit into the compressor first (as suggested by the video), and go on to just remove shims. That does what it is supposed to (btw, after 80k largely city miles the clutch is waaaay out of spec . . . but still functioning, and there is still a bit of material left on it . . . but not much), the clutch still won't engage.

Now realizing I've gone astray, I test the circuit to the AC clutch to see if it is getting power with the AC on. It seems not be, but to double check I go ahead and hotwire (briefly) the AC clutch (run 12V to wire in the video above) and it immediately kicks on and blows cold (suggesting low pressure in the AC system isn't the issue - which I didn't expect because it was working great before it quit).

Now I check the AC fuse - it's fine. Then I check the AC relay - it tests fine.

Then I just decide to start pulling fuses. I find the 15A engine control module fuse (F34 I believe) is blown. I replace it, start the car, AC kicks on, I mess with the AC some more, then it goes hot again (same blown fuse). I replace the fuse with the AC off, and leave it off, drive around . . . no check engine light. I turn on the AC, auto, at a set temp, and don't touch it, the fuse doesn't seem to blow. Who knows how long that will hold (though a guy on another forum said it seemed like his fuse was blowing when he was adjusting the AC).

I assume the issue is the AC clutch just now has some bad internal wiring, so I'm going to replace the whole compressor and take it from there.

While I'm there I'll do the AC and alternator belts and tensioners, which are original as well. I have to think 13 years, and now florida heat, is hard on them.

Hopefully this will help someone.
 

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Interesting problem. Are you sure it was F34?

According to the Wire Diagrams F34 (10A) is for the following:
8/6-8/9 Injection valves, 1.6l
8/77 Fuel volume control valve, D2.0l
8/111 High pressure solenoid valve, D1.6l
8/119 Pressure monitor, climate control system
8/133 Control valve fuel pressure
20/3 -20/7 Spark plug and ignition coil
20/17 Transformer, ignition coils, 1.6l

F35 (15A):
2/22 Relay, climate control system
6/67 Pump, fuel leakage control
6/99 Engine EGR
7/17 Mass airflow sensor (MAF)
7/192 Water detection sensor
8/6-8/9 Injection valves, 4-cyl., 1.8l
8/18 EVAP valve
8/19 Solenoid, variable valve timing, intake
8/28 Turbocharger control valve
8/45 Solenoid, variable valve timing, intake
8/65 Power steering pressure monitor
8/81 Solenoid, variable valve timing outlet
8/82 Solenoid, variable turbo geometry, Diesel
8/114 Valve mixing air/fuel
8/132 Control valve inlet
9/32 PTC-resistor air preheating
 

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Discussion Starter · #3 ·
It is definitely the 15A (and I believe there is only one ECM 15A) - so I probably just got confused. Judging by the rest of what is on the F35 (EGR, MAF, EVAP) and the rest of the codes, I think you're right, F35.

Part of me thinks maybe throw an AC relay at it just to see if maybe that's the issue . . . but I'm pretty confident I did a good test on it, and the original 80k / 13 year old AC compressor clutch seems the much more likely culprit. Parts are on the way.
 

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2007 Volvo V50 T5 AWD M66
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Autogeek - what's an ECU spacer?
The ECUs on these cars are part of the intake for cooling, for better performance some people put plastic spacers on the ECU mount to allow for better air flow into the engine. Or do what I did is remove the stock Intake and zip tie the ECU to the battery tray.
 

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Discussion Starter · #6 ·
So, coming back to this. I confirmed it was the F35 fuse that was blowing. I replaced the AC compressor - I assumed that was likely causing the issue (original compressor, clutch nowhere near in tolerance, fuse blowing seeming to be related to moving the A/C controls, etc.). It's now a week later and the fuse has blown again. My wife thinks it blew on startup, but who knows.

Anyone have any idea where the likely culprit is in this list of items . . . or items I can rule out? I assume I can take off the 1.8L injection valves, as well as the 8/82 Diesel Solenoid, and I believe the PTC is diesel, yes?

I'm tempted to replace the climate control relay just to rule that one out given previous symptoms . . .

2/22 Relay, climate control system
6/67 Pump, fuel leakage control
6/99 Engine EGR
7/17 Mass airflow sensor (MAF)
7/192 Water detection sensor
8/6-8/9 Injection valves, 4-cyl., 1.8l
8/18 EVAP valve
8/19 Solenoid, variable valve timing, intake
8/28 Turbocharger control valve
8/45 Solenoid, variable valve timing, intake
8/65 Power steering pressure monitor
8/81 Solenoid, variable valve timing outlet
8/82 Solenoid, variable turbo geometry, Diesel
8/114 Valve mixing air/fuel
8/132 Control valve inlet
9/32 PTC-resistor air preheating
 

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Discussion Starter · #7 ·
Anyone have any good links to procedures regarding getting to the evaporation system items / wiring (it's back by the fuel tank, correct)? Wiring at the front of the engine seems to be OK (VVT, turbo control valve, etc.).
 

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Discussion Starter · #8 ·
So the fuse started blowing continuously upon turning the car on - which would make it easier to find where the issue was coming from. I remembered I have a power probe with the short finder, so I hooked that up to give it a try. The issue is the short finder detects shorts/grounds. If you follow the electrical harness off of the F35 you find that it goes across the top of the engine and in the middle of the engine the harness is grounded to the top of the engine. Once I got rid of that ground the power probe wasn't indicating a short off that fuse. Prior to figuring that out I unplugged the turbo sensor plug, and then tried to figure out what was wrong with the harness (not realizing I was getting a false reading from the grounds - I didn't realize the detector was a short/ground detector - though in hindsight that is pretty obvious). So now I'm not sure if unhooking the turbo sensor / moving that wire solved the issue, or if there never was an issue in that area in the the first place.

If I had it to do over again I would unhook that ground on the top of the cylinder head and then use the power probe to try and find the short . . . but I realized it was just leading me back to the ground to late - and I was running out of time / brainpower to hook back up the turbo sensor and trouble shoot it properly. Regardless, I put the ignition into accessory (where the fuse was blowing before) and hooked everything up on the top of the engine one by one (leaving off the turbo sensor), and the fuse didn't blow. At this point I have everything hooked up EXCEPT the turbo sensor and the AC is working and the fuse isn't blowing. I drove it around a bit, and the AC still worked (in manual, not full auto).

So we'll see how long the fuse lasts. If I don't have another issue for awhile maybe the issue was the turbo sensor engaging and creating no resistance, thus blowing the fuse. If I don't have an issue I guess I'll hook it back up and see if the fuse blows . . . as that would be the only difference in the system. We'll see.
 

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What exactly are you describing as the "turbo sensor"? Photo?
 

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2007 Volvo V50 T5 AWD M66
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Probably the boost pressure sensor and intake air temperature sensor on the A/C side of the intercooler.
 

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Discussion Starter · #11 ·
Regarding the "turbo sensor" - there is wiring that runs out of the harness at the top of the engine and back to the turbo - it runs parallel to what I believe is a vacuum line also off the turbo that goes to the intake manifold. It has a plug that goes into the turbo. I assume that is: 8/28 Turbocharger control valve (referenced above). Sorry, terminology got a imprecise there after working on it for 3 hours.
 

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Discussion Starter · #12 ·
Funny you should mention that, because I'm hearing a lot of noise / clicking from that area . . . but not sure if that is normal, because normally I'm not standing there listening, with the hood open, and the engine not running.

What do the boost pressure sensor and the intake air sensor correspond to on this list?

2/22 Relay, climate control system
6/67 Pump, fuel leakage control
6/99 Engine EGR
7/17 Mass airflow sensor (MAF)
7/192 Water detection sensor
8/6-8/9 Injection valves, 4-cyl., 1.8l
8/18 EVAP valve
8/19 Solenoid, variable valve timing, intake
8/28 Turbocharger control valve
8/45 Solenoid, variable valve timing, intake
8/65 Power steering pressure monitor
8/81 Solenoid, variable valve timing outlet
8/82 Solenoid, variable turbo geometry, Diesel
8/114 Valve mixing air/fuel
8/132 Control valve inlet
9/32 PTC-resistor air preheating

Unfortunately my VIDA on my personal computer is not working (I need to go back to that thread to see what I need to do), so I'm flying a bit blind as far as the wiring, sensors, and their positioning. When it started blowing continually I thought I would find it quickly with the power probe . . . but then the ground threw me off. I should know better than thinking anything with electrical is going to be simple.

If anyone knows if a proper VIDA scan of this would point me right to it please let me know and I'll just order one and try to set it up again. I had one and the knockoff reader broke before I ever had a chance to use it.
 

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The thing you're describing sounds like the TCV (Turbo Control Valve). It is located behind and below the engine, near the turbo but is not actually part of the turbo. It is not a sensor, but is an electronically controlled valve. It's energized by the ECU to control the wastegate, and therefore the amount of boost. Until you put the pedal down, it is basically commanded to do nothing. Under heavy boost, it's commanded to open, which in turn pushes the wastegate open. The vacuum line you see going to the intake manifold is from the CBV (Compressor Bypass Valve). That's a separate thing, and is not electronically controlled.

Forget about looking up all those sensors and valves in your list. for now. You're tracing a short. And it seems like the fuse doesn't blow when you disconnect the TCV. What else are you trying to analyze? It sure sounds like a bad valve, to me.
 

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Discussion Starter · #14 ·
Gotcha.

Yeah, I'm not sure that the fuse isn't going to blow again - it was fine on a short test drive last night, we'll see if it makes it the day with my wife. With the TCV (and what you're describing is what I saw . . . but it's so cramped back there that I couldn't really tell what I was looking at). It's weird that the fuse was blowing intermittently (perhaps just under boost - which that car doesn't see a lot of driving around Tampa), then blowing constantly . . . but who knows. In looking at the TCV wiring I don't see anything obviously wrong with the wires - but I guess the issue could be internal to the TCV itself, that is definitely possible. I'll keep everyone posted - thank you for the help.
 

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I thought you said it didn't blow after you unplugged the TCV. If it's blowing unpredictably, you've got to keep digging. VIDA is not going to help you here, in fact quite the opposite, it will report problems in components that are innocent bystanders.

One simple thing to try is to disconnect the preheater inside the oil filter/PCV assembly. It's a connector right up front at the top of the unit, it comes in at the side just above the oil filter cap. These are known to short out and blow various fuses, which differ depending on year and model. In your Florida car, it's a completely unimportant element. In fact, many cars have nothing connected to it at all, again depending on year and model, plus where the car was originally delivered.

Tracing shorts and wiring issues ain't fun. But it's even less fun to leave the job to a dealer, who will charge you time to figure it out. Stick at it yourself and save.
 

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Discussion Starter · #16 ·
I will do everything you said above.

So what I said (very unclearly) about the fuse blowing / not blowing is . . .

It was blowing intermittently - it would hold for a couple of days - or a couple of hours. After I did the AC compressor it held for about a week before it blew again. It wasn't blowing immediately upon the key going to accessory (pre-starting). Then, after investigating the harness a bit (moving wires, etc.), it started blowing every time the key went to accessory (pre-starting). At that point I thought "great, now I'll be able to find the short, because it's there, and constant." Then I started tracing all the wiring associated with the F35 fuse. After unplugging and unwrapping most of that wiring (thereby moving a lot of the wiring) AND unplugging the TCV it has now not blown when the car has gone to accessory, and been driven a bit. If that holds then I think I know either: (1) the TCV is bad, OR (2) me jiggling all those wires ungrounded something that was causing the short. I think the more likely answer is (1) because, as I said above, all the wiring, upon very close inspection, looks good and there is no evidence of a broken wire that is shorting out somewhere.

Again, I appreciate all the help - and it's good to know my thought process about doing this myself is a good one - I figured if I took it to the dealer they'd probably be flailing much like I am, but charging me for it.
 

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Go easy when driving with the TCV unplugged. The car will run fine but if you get on it, it will overboost and throw bunches of codes. It's a fine test, however.
 

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Discussion Starter · #18 ·
tmtalpey - you called it. Today the fuse blew again, and tonight I tore into it to check the preheater, and that was it. The thing was burnt and coming apart. I cut off the plug, isolated the wires, buttoned everything back up, and now it works.

Before I forget, any chance an ADMIN could change the title of this thread to include "F35 Fuse" and PTC-resistor air preheating or oil filter/PCV assembly preheater (which I assume is the technical name for that). That might make it easier for someone to find this.

Here's the weird thing. Before I went straight to the plug I tried to see if I would get any indication of the plug being the short using my power probe short finder. I was still getting an indication of a short / ground, but it was taking me right to the ground on the engine block again, it wasn't pointing me to the preheater plug. I guess that makes sense if that the combination of the female end and the male plugs had essentially melted and become an open circuit together (which is what it looks like happened), and it was making its way to the engine block ground (not to a short somewhere else). When I took the ground off the engine block to see if there was another short somewhere, I got an open circuit indication . . . so I really wasn't looking for a accidental short to ground . . . I was looking for the "fused plug" . . . and the short finder couldn't find that except where it grounded.

I left the power probe on the F35 fuse when I pulled the plug off the preheater, and it immediately went from "short/ground" to "open circuit." My assumption is that took the block ground out of the loop .

I didn't analyze it after I cut the plug to see if there would be anything different. I assume not.

I'll be interested to see if I get a check engine light with the plug cut off. If so I'll have to consider if I want to put the heater back together.

Anyone know if you can just buy the heater, or if it requires buying the hole system? I've done the PCV system once - at like 30k miles. I guess I could do it again, but if there's no check engine light without it I don't think I'll be doing it.
 

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Well, good! But I don't understand why you cut the plug off. If you press on the wire clip, it pops right off the connector. Are you saying the connector itself was melted, along with the resistor? Yipes.

Changing the thread title isn't very meaningful - search goes much deeper than just titles, and "F35" is not necessarily the same on all our cars. There are dozens of things hanging off that fuse, as you've discovered there is no simple process to figure out which. This issue has been discussed in the past here btw.

As I said, you'll be fine without the preheater and it won't throw any codes. But bear in mind that the PCV in general is a common failure point and you may need to replace it someday for non-electrical reasons. No, internal parts for the PCV are not available, although some enterprising eBayers have offered the diaphragm, if you're up for a challenge should the day ever come.

Here are some links for background, search is your friend for more:
https://forums.swedespeed.com/showthread.php?589559-What-is-this-sensor-on-the-oil-filter-housing
https://forums.swedespeed.com/showt...fix-for-the-S40-V50-(others-affected-as-well)
 

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Discussion Starter · #20 ·
The inside of the plug was totally melted (but looked fine from the outside). One of the male prongs internal to the heater came off with the plug, since it wasn't reusable as is I cut it off and heavily insulated the wires from each other. I'll have to figure out how to get another plug if it ever comes to that.

I think I would have been well served to search more after I had better isolated the issue, though I'm not sure exactly how I would have done that. Hindsight is always 20-20.

I imagine I'll just hold off for my PCV system to go again, and if it does I'll replace that whole mess again. Knock on wood the replacement ones seem to hold up better - like I said, mine's been going about 50k miles.

Thanks for all the help!
 
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