I bought a house that is 10yrs old and the compressor was just replaced a year ago. I bought a programmable T-stat and now occasionally the compressor will turn on to cool the house but the air handler does not turn on. You hear some noise like coolant in the lines running but the air handler fan doesn't come on. It does not happen all the time but it been happening more often as the days go by. What could be the problem?

The fact that it will start any of the time tells us that the motor windings are good. From the age of the unit, I would bet that it has a Permanent Split Capacitor motor. It sounds to me as if the run capacitor could be bad. If you try to start the motor and it just hums and then shuts off (on an internal motor overload) then it probably is the capacitor. This is a silver object with two or maybe three wires going to connections on one end of it. Most parts houses will sell you the part. BUT!! These capacitors can store an electrical charge that will knock your teeth loose. Your best bet if you are not knowledgeable on this sort of thing is to get someone who is. Otherwise, be careful and good luck. Hope this helps