fan not engaging >?

[Vazquezp]

so i have had this problem for a while now and have been putting it off> well no more; my AC has not worked properly for almost 6 mos. and in Houston, TX thats a problem. i got it looked at by a mechanic and they arent sure what it is> The mech. said that my fan isnt engaging when the ac is turned on. i didnt know it was suppose to<>? also the AC compressor doesnt disengage when the ac is turn "off"
can anyone shine some light this way<>

[cooljess76]

The fan has two speeds. The high speed relay should kick it on when you turn on the A/C, the low speed should be triggered by a temp sensor.

[Vazquezp]

hmmm thats new to me; ive only heard the low speed on the fan which is every now and then; so maybe its the relay that i need to replace>>?