Arrived on site to perform combo maintenance on 2004 system. Cycled system for heat. Checked indoor unit electrical and system components. Temperature rise across heat exchanger is slightly above the range. System is slacking on return air flow which is what could be causing the higher temperature. Cleaned blower assembly as well as heating compartment. Blower wheel is slightly dirty. Pulled evap coil cover to examine heat exchanger and check coil. Safety inspected heat exchanger. Heat exchanger passes safety inspection for today, but system is older and is getting slightly hotter than it should. Evap coil is very dirty, and is not only causing an air flow restriction but also poor air quality inside the home. Replaced 1 inch filter. Cycled system for cooling. Checked outdoor unit electrical and system components. Primary and secondary motor control have been recently replaced and are still within range and in good condition. Amp draws for compressor are very close to going over allow