The Hubble tension continues to motivate modifications to pre-recombination physics. We investigate an early dark energy (EDE) scalar field that is exponentially coupled to photons before recombination. The interaction modifies radiation dilution and yields a non-standard cosmic microwave background (CMB) temperature–redshift relation $T(z)=T_0(1+z{)}^{1-\beta }$. We specify an exponential potential that realizes the assumed radiation-era scaling solution and consistently perturb both the covariant energy-transfer vector and the Klein–Gordon equation. The photon continuity equation acquires a source term proportional to $(4\sigma /3)\delta \varphi \prime$, whereas the photon Euler equation contains no direct momentum-transfer term for the unweighted photon energy–momentum tensor. Within a restricted smooth-field regime, we evaluate the background by direct quadrature and construct illustrative temperature and polarization peak-shift templates. Using the high-precision Planck acoustic scale, we obtain the semi-analytic acoustic-scale consistency estimate $|\beta |\lesssim 1.8\times {10}^{-3}$. This estimate is not a likelihood constraint; a quantitative analysis requires a full Boltzmann implementation.