How can I fix my aircondition in my car?

Need help in finding what to look for about my mothers car. The aircondition will not come on unless you put the fan on all the way. I have some people looking at it but it will cost a lot of money in which I do not have. My mother's car is a '93 nisson ultima.

The problem: the fan only comes on at full blast on number 4 but as soon as it is turned on the compressor kicks on at settings 1,2,3. Switch settings range from low (1) to high (4).