The thermodynamics of galaxy clusters are a powerful probe of their evolution over cosmic time. Cosmic Microwave Background (CMB) photons scatter off hot electrons in the atmosphere of these clusters creating the Sunyaev-Zeldovich effect (SZe) that can be used to probe the physical state of the intra-cluster medium (ICM). As the ICM can reach temperatures of 20 keV, a correction reflecting the relativistic velocities of the electrons applies to the SZe spectrum. By measuring this correction we can achieve a redshift independent constraint on the electron temperature in clusters. Because sub-mm spectrometry provides continuous spectral coverage needed to unambiguously measure this relativistic correction, we use the SPIRE Fourier Transform Spectrometer on the Hershel Space Observatory for our analysis. In this poster we discuss the motivation for spectral measurements of the SZe and the preliminary details of our analysis.