I don't think this is weather related. According to the Jeep Dealer there are leaves and debris that are clogging the area and the only way to repair it is to pay $800 to REMOVE THE ENTIRE DASHBOARD. Then while they have the dashboard out they want to install a new evaporator coil (I think) just to be sure it is working. That's an additional $238 for the new evaporator coil. It is a 2000 Jeep Grand Cherokee with 178,000 miles.

Some of those you can watch actuate near the hump in the floorboard,back underneath. If it moves all the way when you switch from cold to hot,it's not the blend door. CAN be a partially clogged heater radiator.
IF you can get the hoses identified, you can take a water hose and backflush thru the hose that returns to the water pump.
This will blow debris out the heater hose which comes from the thermostat area, in reverse of its usual flow. don-ohio (:^)

see the diagram attached and proceed according for troubleshooting.

The drain hose that allows moisture to exit the HVAC system is clooged with debri and prevents the water from exiting the HVAC area. Open the hood and you will see a rubber hose that has an opening on the end. Use compressed are to blow the clogged area free and allow water to exit.

If the abs light is on and the horn does not work generally it's due to a broken "clockspring" in the column. You can replace that but definitely need a haynes or chlton manual to use as a guide. If you do the repair without instructions or don't follow them exactly, the air bag can deploy in your face (hurts a lot....dangerous). If only the horn isn't working, I'd get another opinion before allowing anyone to do the job. The clockspring and airbag are separate items and I don't see a reason to be replacing the airbag (unless the dealer found something I'm unaware of, but I doubt it).

yep sounds like its failing again , if you have to replace it again I would go for a non standard one and go for a heavy duty type .

Your temp should run about 210 degrees (f) If you need to keep the heat on to keep the temp down likely the radiator is partially obstructed either externally (leaves or other debris) or internally (rust or calcium deposits).Most over the counter flushes don't do much but it's worth a try. Generally the best option is to have it professionally flushed or replace it with a known good one from a scrapyard.

have a local repair facility look at the front and rear universal joints

Unless you live in an extremely cold climate (sub or close to sub zero) I'd recommend using at least a 10w 40 oil. The first number indicates how well the oil pours (flows) at freezing, the second is how well it protects at operating temperature. Your other option is to use a 10W 40 synthetic which actually flows and protects far beyond the #'s on the container on both ends of the scale. One reason some manufacturers have specified a lower first number is because they feel that will keep the piston rings free.
In reality, any good oil will do that (non-paraffin base) and any of the synthetics will do it better. I live in an area where we get both very cold weather and also some very hot weather. I use a 20w 50 synthetic and have never had an oil related problem (my engines regularly go over 350K and vehicles are replaced for other non engine related reasons such as body rust)

The boot seal that is on the pedal hinge and the brake booster might have ripped due to the extreme temps. Check the seal and make sure its still good.

This could be a simple faulty sensor to something as complicated as a clogged cooler or line. Check your fluid level, the next step would be to have the fluid changed. Most transmission shops will check for clogged lines or problems at little to no cost. This is the avenue I would take. If the transmission is still under warranty take it to the dealer to have it checked. It could be the transmission cooler being clogged with debri. Use a garden house and spray water from the engine area toward the front of the vehicle to loosen and remove anything clogging the radiator and transmission coolers.