Blows cold but shuts down no freeze up

need freon

Bad fan motor. Multi-speed motors have a set of windings for each speed. Your high speed is bad so the only solution is to replace the complete motor. When motors are going bad they will over heat and kick out on the heat safety. As it cools back down it will start again for a short time again until it gets hot again.

Have a look inside fridge compartment (especially the "roof", if it's a top-mount freezer) & see if you can see any ice build-up (look inside vents that allow cold air into fridge from freezer section. Also, if top-mount freezer, look inside the freezer compartment for ice build-up on "floor", inside vents, or on back wall. These symptoms, combined with water dripping from lots of the "roof" of fridge section (in a top-mount freezer model), can mean several different problems, so best to re-post with more info/symptoms included.
If there's no ice build-up (& the dividing area between fridge & freezer sections isn't particularly cold, which otherwise might indicate hidden ice build-up), it can be as simple as a plugged or obstructed drain tube, which is VERY COMMON. Easiest solution for this latter problem is to use a flexible plastic tube (think similar type as attached to aquarium air pumps), stuff it into drain hole, and blow on the other end. Sometimes you have to blow quite hard to clear an obstruction or complete blockage. If you can't clear the drain tube, it's likely a different problem. Again, a re-post with more info/symptoms will help narrow it down.

Don't really understand what you mean by roof top duct unit .if it's a roof top unit and water is leaking down your vent then you have a clogged drain line .

if the ac system is very strong and there a lot moisture in the air the a'c evaporator core will freeze up and stop air flow threw the cold core only use the recuiculation part to cool the car down about 5-10 min the turn the recuit off

may be a few things try checking the a/c lines when it does the shut off thing are they freezing up? may need a dryer. is the fan coming on at the radiator when the a/c comes on? it needs this to keep the head pressure down. does it drip water when the a/c is on under the car? may another sign its freezing up.

take a garden hose to the evaperator,probably dirty.

You are low on refrigerant.

Yes and no .. Freezing temps should not affect your A/C at all ... BUT .. there is a freeze control box, its called a control unit to prevent itself from freezing up and burning out, take down the lower cover and you will see it. Your problem is more likely to be more central since neither are working Thermostat or even the control box's in genera, even could be a freon problem if the cold weather was really bad and you could have a leak on your lines, check it out and see what you got!

There is a blend door motor on top of the housing. If you open the glove box, and look to the top of the housing near the left rear of the glove box, you should see the blend door motor. You can check it at this point. Also check the housing, as I have seen a number of these with a damaged or broken housing.