The objective of this work is to propose a thermal model for predicting the average air temperature inside the passenger cabin of a small-sized car that uses an HVAC system. The adopted model is a lumped parameter model that accounts for nine heat sources acting on the cabin. Additionally, the model presents a methodology for calculating the temperature at the evaporator outlet considering a linear temperature drop between its inlet and outlet as a function of sensitive heat, latent heat, evaporator input temperature, absolute humidity, enthalpy and specific heat. Sixteen experimental tests were con-ducted on a commercial vehicle under various operating conditions to validate the presented model. The maximum average relative deviation between the experimental and theoretical results was 17.73%.