Pulled the plug, made no difference other than throwing an AWD malfunction error.

Yeah, I unplugged it, threw an error on the dash, but didn't change anything as far as driving. Wheels acted like trying to grab on pavement when turning... as if it's in a 4WD in 4WD. 

This probably indicates a bad (Active Torque Coupling (ATC) solenoid.  This is the front part of the RDU and controls how much the rear axle connects with the front.

I was leaning towards this answer.   It could be the valve, but it may also be a small, very slow leak that you will never find on your own.  The only way to find the leak itself is to perform a dye test, where they inject a dye into the A/C system.  The leak will show under ultraviolet light.   Sometimes the seals dry out causing the leak over time, eventually resulting in total cooling failure ( No A/C ) due to complete loss of refrigerant.   I had very similar symptoms on a couple of different brand cars over the years.  Acted just as you initially described.  It was a leak.

There are plenty of pictures of the installed CVF front mount intercooler  ( FMIC ), and install instructions on-line.  You just have to do a search.   As far as performance gains, the purpose of the FMIC is not for a performance gain, not directly.  The purpose of the FMIC is to keep the charge temp into the intake cooler, for a longer period of time.  If you want performance gains, then there are multiple " bolt-on "pathways to get there.   1. Performance Tune   2. Larger Turbos   3. Increased Fuel Flow   4. Larger Exhaust   Some of the above options require for them to be used together  

Much of this issue could also be attributed to a low refrigerant level.  As the car runs a while and gets hot, the refrigerant expands as it heats and can work better.  It certainly could be the valve, but buying a refrigerant pressure gauge at an auto parts store and checking the level/pressure while its running could rule this out.  Even without a major leak, refrigerant levels do drop due to evaporation through the hoses and tiny leaks at the fill valves on the high and low pressure side.  If it is low, adding some gas could get you 5 plus more years without a problem.  

I disabled traction control through dash settings. I may try your suggestion on unplugging the connector if I can access it.

Welcome.   With a used PTU installed clouds the diagnostics.   I suggest you electrically disconnect the RDU coupler and test drive it like that. What method did you use?   I can get onto the interstate and depending on how hard I accelerate the power to the rear will stay on up to around 60mph.      

Bought a 2015 Ford Edge SEL 3.5L a couple months ago. A few days after buying it, I drove about 50 miles and got an “AWD Disabled” message. I clicked okay, but it came back, then the wrench light showed up and it started to smell like propane. I pulled over, let it cool, and drove home. After that, the message would come back after about 10 minutes of interstate driving, until it eventually started making noise after a week or so.   I contacted the lot I bought it from and they seemed willing to help. A scan showed P183D (PTU over temp). We both figured it was the PTU, but decided to try changing the fluid first. That helped for about 2 days of driving, then the AWD message came back.   Took it back, and they said the PTU was likely damaged, I agreed. I asked for a replacement with a warranty, but they ended up installing a used PTU with no warranty. First interstate drive with that unit, AWD Disabled came on after about 20 minutes. A couple days later, it was down to about 10 minutes again. Even after clearing codes, P183D keeps returning, especially after interstate driving. Note there's also a U3003-16 low voltage in the traction control, but I don't know if it's related.   Now I’m getting a rubbing/grinding type noise, no smell. It sounds like it’s mostly coming from the rear this time, with occasional different noise from the front. The issue seems to show up more at higher speeds on the interstate, and that's when it threw the last code.    My own mechanic checked the differential lube and said it seemed fine... thinks the replacement PTU might have been a bad unit. The lot owner is somewhat working with me, but I told him in my opinion either the replacement PTU is bad, or something is causing them to fail.   When I got home, I did some tight turns in a parking lot, and it behaves like a 4x4 on dry pavement, it grabs/binds when turning at low speeds. The dash power distribution screen shows all 4 wheels engaged up to around 50 mph. I disabled traction control... I couldn't tell a difference.   I connected FORScan and logged what I could (attached), but I couldn’t find wheel speed PIDs, maybe my hardware. From what I can see, it looks like the rear is being engaged more than it should be, even at higher speed.   So my questions/theory: The replacement PTU could just be a dud on its way out Or, something like the RDU/rear drivetrain is causing the system to stay engaged, which is overheating and killing PTUs   Has anyone seen a bad RDU or rear driveline issue cause repeated PTU failures like this? I’m hesitant to put another PTU in it, especially a new one, until I’m sure there isn’t an underlying issue that will just destroy it again.   For reference: All 4 tires are the same size, brand, and wear No visible PTU leaks on this unit like the last one No burnt smell like the first unit Replacement PTU supposedly had fresh fluid At this point it almost feels more like a rear driveline or AWD control issue than just a PTU, but I’m not sure. Any advice or similar experiences would be appreciated. Thanks.

Agree, the variable displacement compressors symptoms are very different to the ON-OFF clutch type.