4A vs 4h (4x4 knob)
 

Forgive my ignorance on this topic, my xlt has 2w, 4H and 4L. The manual says do not use the 4H or 4L on dry pavement because it could cause issues, which is fine, I don't plan on using 4x4 on dry pavement.

My question is I live in ROchester NY, we get a fair amount of snow. When the ground is snow covered, I used to put my old expedition in 4A

What is recommended when you don't have 4A? Let's say the road is snow covered for a few miles, then clear, then snow covered again. Do I have to flip between 4H and 2H everytime I hit any sort of dry pavement?

Is 4L and 4H more for off road and the 4A (which I don't have) more for snow?

Do other trim levels come with 4A?

4H is fine on dry pavement for short stints, such as a mountain pass with spotty snow. It's not recommended to leave it in 4H for daily driving. People use 4H for racing, towing needs, and any other condition you need better traction.

4A has a differential between the front and rear output in the transfer case, 4H does not. 4A is like an all wheel drive and can be used on dry non slippery surface like dry pavement, 4H locks the front and rear output together, using it on non slippery surface put's a lot of strain on the drive train and steering. IMO with many many years of wheeling use the 4H when you need it for traction only and prudent speed for control.

The only time I've found 4A particularly useful was at highway speed in the mountains with 33-degree wet roads and falling snow, because speed of traffic was to high to slow down to snow/ice speed but the pull from the front can help keep the rig straight. Otherwise, I just leave it in 2H and use steering and throttle control to keep things in a mostly straight line; when that starts getting to be a chore and I'm under 20 MPH, I'll flip into 4H (and that's been true of several 4WD rigs both here in Montana and in northern New England). I'd much rather have a bit of oversteer warn of traction limits than understeer.

After a bit of gravel yesterday, I will admit that the power and boost from the 3.5 is probably going to require a very, very light throttle touch in slippery conditions.

The 4x4 system between the truck models is the same. 4A simple lets the computer decide to engage 4H when it detects enough difference in wheel speed between the front and rear axles and disengage 4H when the computer thinks you don't need it anymore.

4h will bind in tight corners and stress the components. if going straight or pretty straight - like on a highway, 4wd on dry is just fine. I know guys who left 4wd on for a LONG time by mistake. all was fine.

Not exactly sure what you're saying, but if your claim is that the standard 4H system on XLT and lower trims is the same as the 4A found on Lariat and above, that would be incorrect. They're completely different systems.

The XL and XLT have a different transfer case than the Lariat and above because of 4A so they do not have the same 4x4 system.

Is one version tougher/better? Seem the same? Meaning is one 4x4 system preferred?

It's actually possible to drive in snow in 2WD.