There are a couple of things you could try that might save you a service call:
Have you changed your filter? A dirty filter can seriously compromise your unit's ability to work efficiently.
Turn your unit off and reset your breaker. Power outages, power surges or bad weather could cause your unit not to run as it should. If you are not familiar with your breaker box, DO NOT ATTEMPT THIS. Call a professional.
If you're still not comfortable, call us and let us come take care of it for you.