I haven't run into that but to be on the safe side you can either call or go down to the dealership with your VIN and they can give you the factory part numbers. From that the parts stores can cross reference to their part numbers.
BTW, it's OK to bring up an old thread, it keeps it all consolidated so you can do less searching for the info and add new info as needed.
I wanted to add a couple of things and ask my own question.
First, the upper and lower idlers ARE different (2007 Compass 2.4L CVT w/AC)
The upper is smaller diameter than lower. (I think 65 vs 70)
Second, I just did my wife's 2007 Compass. It was making a horrible noise from the front, we smelled burning like brakes, and it had a nasty grinding noise at low speed decel. When it rolled to a stop, the noise stopped.
I thought CVT was going bad for sure. I put it on my buddies' lift and we ran it with stability locked out, running all 4 wheels. I had just a few months earlier (about 95K miles) put on both rear wheel bearings. They were also making a really horrible highway noise, that I first thought were rear rotors.
I thought it might be front wheel bearings, but those are not so "easy" to do, as they must be pressed in, and that's one thing I don't have at home. (yet, but Harbor Freight is calling) Anyway, on the lift the noise did not seem like it was coming from there, and we detected no major runout in the front.
A mechanic's stethoscope on the front made it very hard to figure out where the noise was coming from, alternator, or AC compressor. But the noise was there with AC on or off, although I'm not sure where the clutch is on the compressor; the plug for it is on compressor's rear. Its bearings might have been bad. The noise also seemed like it came from the alternator, but they are hard mounted to the same bracket, so it was hard to tell.
I amazingly with a 40 off online coupon got the alternator cheaper at A_dvance Auto than at R_ock A_uto by about $20. So these alternators do now have the clutched hub on them, which allows the alternator to freewheel relative to the belt to reduce inertia on decel. I guess this is to save some gas maybe. I don't know if it really helps the belt system at all. But that is why the noise came out really bad on decel, especially at low speeds. Another lesson learned.
Well, old alternator out, you could tell immediately the hub turned poorly compared to the new, so the noise was gone. No CVT replacement, Thank God!
The video talked about on You_tube was very helpful, but I dropped the alternator down more towards the middle of the engine, which seemed to have more room. I could not push the AC compressor down enough, even with the drier unbolted and the tube clamps up next to the PS reservoir unbolted and loose. In retrospect, it may have even had more room if I had unscrewed the oil filter, which was right behind it. If I had had an extra new one ready, I would have. I had tried to unbolt the bracket itself from the block, but after removing the lower bolts, I found the upper end was one long piece to the PS pump, so that seemed like more work than it was worth.
The help and research on this site and others was great. I had been not sleeping nights thinking of R and R'ing that CVT. Bad how an old(er) dog immediately suspected the transmission, but an unrelated subsystem that was new to me was root cause.
Now my problem: I bought new belt, idlers and tensioner to change while I was in there. The belt was Dayco 50610005, which R_ock A_uto said would fit 2007 2.4L, w/AC and CVT: Effective Length 100.59. I could not stretch this thing to fit, no matter how I tried. I ended up putting the original belt back on so my wife could drive it. I also saw that R-=A had a DAYCO Part # 5061015,Specifications Effective Length 101.58, but this was listed for a manual trans. Does anyone know if this listing might be wrong? About an inch difference would appear to be how much more I needed. I had the tensioner fully retracted to its loading position, but I could not get it on. The 100K OEM belt went on fine with just a little stretching to get it over the last pulley. I didn't see any cracks in it, so I'm sure it is fine for now, but I need to resolve this before too long.
What a blessing the help on this board is. Also I should mention another minor pitfall. The replacement tensioner used a smaller bolt 15m vs 16mm head to adjust its position. It was otherwise dimensionally the exact same, as far as I could compare it to the OEM.
Sorry for the long winded response. The job took quite a few hours. I could go faster now if I did it again, since I know better what to expect exactly, but it had some VERY cramped quarters that did not leave me a lot of wrench swing room to get everything out. And some of those attachment bolts are way longer than they needed to be.