This paper presents analysis of the role and effect of internal heat exchanger (suction line heat exchanger) on performance (capacity and COP) of vehicular climate control systems. Cycle analysis presented at the beginning is supported by experimental results presented in the second part of the paper. The system examined experimentally is a typical R134a air conditioning system for a medium size car. Compressor is scroll, condenser with microchannel tubes and evaporator is plate type with four passes. Special care was taken to measure and analyze effect of exit vapor fraction (quality) of refrigerant at the exit of the evaporator. Four cases were explored: baseline (without internal heat exchanger) and three different effectiveness and pressure drop of internal heat exchangers. Vapor fraction (quality was changed in the range 0.75 to 1 and superheat up to 20°C. Results demonstrate increases in capacity up to 13% and efficiency up to 12% compared to baseline system (without internal heat exchanger) and COP and capacity maximizing exit quality in the range 0.95 to 1.0.