Reversible heat pumps for electric vehicles are being developed by the car industry to address cabin heating and improve energy efficiency compared to electric heaters. For this new application, the front microchannel heat exchanger (MCHX or flat-tube heat exchanger) of an A/C system acts as an evaporator on the heat pump mode and can operate under frosting conditions. The MCHX is particularly sensitive to frosting. Consequently, a MCHX model that can predict performances under frosting conditions is required. This paper presents a dynamic pseudo 3D model of a MCHX including frost growth. Frost is modeled as a porous layer that is subject to heat and mass transfer. The model successfully predicts thermal performances for nonuniform frost growth. The model needs now wider experimental validation and could be used as a design tool.