The authors have developed phase modulation atomic force microscopy in constant excitation mode capable of simultaneously imaging the topography and energy dissipation of a sample surface in a liquid. This setup utilizes a fast, low-cost sample-and-hold technique to analyze the oscillation signals of a cantilever. The proposed circuitry allows us to measure the local energy dissipated by the tip-sample interaction during imaging. The energy dissipation image exhibits a material-specific contrast for a polymer-blend film.