When I turn on defrost the steering will not work and the battery light comes on?

Try it with the AC on and I suspect you'll have the same symptom. The AC runs in defrost mode. It sounds like the AC compressor is putting enough extra load on the engine to slow the serpentine belt. The generator will turn too slowly, so the "Battery" warning light will turn on.

With the engine off, put a chalk mark on one of the pulleys to make it easier to see, then run the engine and watch that pulley while a helper turns the defrost on and off. I'm betting you'll see that pulley slow down. That would explain loss of power steering assist.

The logical suspect would be a worn drive belt, but first check the tensioner pulley to be sure it's holding the belt tight. With the engine off, tug on the belt to make the pulley rotate on its pivot, then see if it pulls the belt tight when you release it. Rust or corrosion in that pivot can prevent it from holding proper tension on the belt.

Even though the symptoms are different, check out these related articles:

https://www.2carpros.com/articles/car-squeaking-noise

https://www.2carpros.com/articles/serpentine-belt-tensioner-replacement

You can unplug the front plug on the compressor, but if the AC isn't working now, that shouldn't be necessary. The compressor won't get turned on if the refrigerant has leaked out. The rear plug is for one of the pressure sensors that help regulate the cooling by cycling the compressor on and off as you drive.

The bigger concern is why the belt is coming off. A loose pulley on the alternator can do that, but it's rather uncommon. I put these drawings together last night for someone else with a belt squeal, but they might help you too. These are supposed to help explain a "tipped" or "turned" pulley, including one that's loose or wobbling due to a worn bearing.

Drawing 1: A common place to find a tipped pulley is the spring-loaded tensioner. The mounting bolt and the hole it goes through can wear, then the arm the pulley is bolted to will tip from the tension of the belt pulling on it.

In the lower belt routing diagram, the red curve shows the area the belt runs off-center.
To identify that, sight straight down over the top pulleys as shown in the top drawing. The red area shows where you'll see the edge of the belt peeking out. A belt off-center by as little as 1/16" will set up a squeal as it slides across it as it goes around it.

Drawing 2: The arm of the spring-loaded tensioner is built on a flat, round metal plate that sits on a flat mating surface on the front of the engine. A common problem occurs when that assembly is replaced, and corrosion or other debris becomes trapped between them. That turns the pulley relative to the belt, as shown at the top left of the second drawing.

The same thing can happen to the idler or tensioner pulley when their bearings become worn or sloppy. The resulting squeal can be caused by any smooth pulley. Look for a turned or wobbling pulley on the water pump too.

Drawing 3: A majority of new pulleys are painted black. That paint wears off over time where the belt runs over it, especially on the smooth pulleys. In the third drawing, the belt on top is running under the pulley, in the normal location. The lightest gray area is where the paint has worn off. The belt, (darker gray), is right in line with the worn area, indicating that pulley, or the one right before it, is not turned.

In the lower drawing, the belt is not centered over the worn area. That's something new that most likely started occurring at the same time the squeal started. Look for the telltale shiny area where the belt is not running.

Okay, if turning on the AC or defroster causes the symptoms to occur, the AC system must be charged and working. The compressor does put an extra load on the belt and can cause it to slip, but it shouldn't cause the belt to jump off. That slippage is not always accompanied by a squeal.

Let me know if you see anything related to the pulleys that could make the belt run off-center.