From the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Journal Vol. 48, Nov. 2006:
Although it’s known theoretically that cleaning a coil can result in energy savings, little actual testing data and research exist to prove the point. As a result, building managers often ignore or reduce resources devoted to air-handler maintenance when faced with budget constraints. If proper maintenance is an important consideration in overall energy costs, conserving in that budget area can be self defeating.
Through [...] privately funded testing, monitoring and analysis, we [at ASHRAE believe we've] found a methodology and regimen that proves maintaining air-handler components in a clean condition can save energy dollars and improve other building parameter changes and efficiencies such as improved dehumidification and comfort, along with less mold and bacteria. Thus, we are encouraging IAQ environmental parameter improvements, better tenant satisfaction, and increased worker effectiveness.... Read More (PDF) - Study Verifies Coil Cleaning Saves Energy - ashrae.org