How often does it cycle? If it cycles on and off often, that means it is low on freon. I would suggest you to service the system yourself. You can buy all these tools at harbor freight and keep it for future usages..
1. Vacuum pump--->
http://www.harborfreight.com/two-sta...ump-66466.html
2. AC guages--->
http://www.harborfreight.com/a-c-man...set-92649.html
I converted mine to envirosafe freon which is basically similar to redtek. These freons are larger molecules and suppose to not leak like r134a. You can get these here pretty cheap.
http://autorefrigerants.com/co00033.htm
Don't let air conditioner system scares you. Its not hard. On youtube they can show you how to service it. However if you system is old, I would suggest you to change to a new drier and expansion valve, and new o-rings. Do this before you evacuate the system via the vacuum above.