Yes, there is a lot you can do before making the fatal call. Here's a short list and is not conclusive but maybe it will save the $150 service call:
1. Check the wires in the indoor and outdoor unit to see if there is an end burned off
2. Clean the condenser coils on the outdoor unit
3. Clean the evaporator coils on the indoor unit
4. Check the circut breaker
5. Check the disconnect near the outdoor unit
6. Open the outdoor unit and find the contactor (listed on the wiring diagram), push the center of the contactor with a screwdriver and see if the compressor will run
7. Use an electrical tester to see if power goes to each point on the wiring ladder
8. See if the lines to the outdoor unit have any difference in temperature (the small line should be warm and the larger one should be frosty
9. Hold your hand over the outdoor unit and see if the fan is blowing any heat out.
These things will give you a start on the unit; let us know what you find and we may be able to help you fruther. Two cardinal rules in air conditioning service: Clean first, gas last and 7 out of 10 times there is a wire burned off or circut breaker off.