2001 Galant manual air conditioning. In position 1 and 2 ac works blower does not work in position 3 and 4 blower works ac does not work.

Blower motor resistor bad ! Watch this video , Blower Motor Problems Auto Repair Help

Start by checking fuses & work on getting the fan or blower
working & all havc vent doors working
After that your ready to work on the refrigerant side
No vehicle experience or system reference material,you
may need help at a shop

You'll need to have a mechanic check the system to see if it is low on freon, or if you have an electrical problem.

I think you should buy repair manual first for your vehicle after that it will be easy for you to solve the problem. Check the link may be you will get something useful here Complete 2001 Mitsubishi Galant Workshop Repair Service Manual

problem one the blower positions first it could be the blower resistor or possibly the switch second problem no cool air there is a heater shut off valve under the dash on the right side of the radio if you change the temp control from cold to hot and hot to cold and hear a clicking ,grinding noise this valve is bad and not shutting off the hot air to the system making your a/c feel warmer , or a/c system has a leak somwhere and will have to be recharged and traced to repair it

MY 2003 MALIBU AC WORK VERY COOL FOR ABOUT ONE HOUR AND THEN TURN A BIT HOT AND THEN NO AIR COME OUT WHY I HAVE CHECK THE FREON AND ITS OK .

You could remove fuse 25 (30amp) in the underhood fuse panel, but then no blower for AC, heat, or defrost. Need to replace blower regulator.

You might have a bad speed selector switch, or your blower motor resistor is faulty.

heater controls could be gone

I have an 01 convertible lxi that just did the same thing..... You can go to an auto parts store or in my case, I went to Firestone and had them replace the blower resistor. My air now works on all settings.