First, schedule a cleaning for your filter each week if there is lots of dirt in the air. And, replace the filters in the furnace on a regular basis. The aluminum fins on the back air conditioners can also be cleaned in this process.
While you are cleaning, examine the HVAC coils. Make sure they are not corroded and that there are no leaks. If they are no corroded and leaks are found they may be fixed quite easily by brazing. If, however they are corroded beyond repair they can be easily replaced. HVAC coil replacement is a nice way to save money in this economy.
It is common for many people to turn to the original manufacturer for the coils. What can happen when you attempt to buy original coils is the factory that made the make and model years no long produces them and they do not have any of those coils in stock. Taking the time to produce one set of coils is costly as most factories are setup for mass production. In addition, the delivery for the production of one HAVC coil will obviously take longer.
As an alternative to original coils, consumers can have custom coils manufactured for the older HAVC models. And often the cost for these generic coils are much cheaper that original coils. For additional information go to hvac units and services. Here is video on the process involved in making HVAC Unit Coil Replacement Manufacturing Process