This message goes to all of you who had posted relevant problems (Supersix1, Swanne, Dilbert5)...
I have been through all of the "in's and out's" of my 98 Explorer's AC issues and finally found the problem to be the blend door.
Below are symptoms and causes learned from this escapade...
Both hoses through firewall are hot when A/C is on? This will be your flow-through valve (it is in your engine compartment and attached to on of the two hoses sticking out of your firewall)... just replace it! It can be done in five minutes.. It is common though that something may be blocking the valve from closing... is your water rust colored.. I found this to be the case in mine and after replacing the valve, I drained and flushed the cooling system with an additive to dissolve corrosion and replaced the antifreeze coolant. i also added a corrosion and leak inhibitor found at any local automotive store.
Blowing cool on cool days and hot on hot days....? Believe it or not... if your system is charged, water is condensing, compressor working, etc... the blend door in the heater plenum will make it feel like the a/c is not working when it allows the hot air to flow through... This was the case with mine. I found several articles with people complaining about the fact that ford used crappy parts in a place so hard to get to... The blend door is a part easily ordered from Rockauto.com for $20 but in my case would have been $800-1200 labor for replacing it. In fact, the heater plenum in mine could only be removed after removing the whole dashboard and steering column. A real pain but great lesson in understanding the way it works!
In fact, once I got the dash and everything all out, I was surprised to see that the heater box/plenum actually had a few more screws/nuts that had to be removed in the engine compartment on the firewall... Oh yeah, not the mention that it was heat sealed shut and had to be reopened by cutting the seam with a torch & a hot razor... (the dealership wanted $290 for a new heater box, but it was just the plastic door inside that was broken)
If you take it on, just be careful and patient, there are too many things that can break that will lead to you having a bigger headache... Before diving into to such a project though, do yourself a favor... take the blend door motor/actuator off and test it? It is right behind the glove box (which can be opened fully by pressing in the sides) and can be pried off just with a screw driver as it just snaps into place.... turn you key to the "on" position and moved the temp dial... if the motor turns when changing temp (without clicking.... the most common problem being stripped gears) then the problem is the blend door that it moves. Take a small mechanics pen/mirror and see if you can angle it to look at the top of the pivoting point of the blend door... One that is not cracked/broken will look like a elongated "D"
I did everything I could from having limited automotive/mechanical knowledge but ended up ordering and replacing the control assembly, heater flow-through valve, charging the system, replacing the actuator, etc... In the end, I just asked a local repair shop to diagnose the problem and paid him $50 for his time and effort... I should have done this a long time ago.
I know that these things could seem overwhelming at first, but in the end... the sense of accomplishment and the fact that everything works just the way it did when I first purchased the vehicle made the long weekend well worth it.... if you should take on the project and need any help.. I'll do what I can to post advice on what i had personally encountred.... Best of luck to all of you!
John
buttt it's been doing it forever kinda like what you said just one random day blowing cold air it switched to heat and now if its like 0-70 degrees it will blow cold air(or cool but I couldn't make it freezing if I wanted it) but anyway the only thing that works is the heat if its ice cold out side I get normal heat and sometimes even on low to medium settings it gets VERY hot in the car. 
