The objective of this testing is to investigate three phase (3-Φ) rooftop packaged air conditioner (A/C) units performance during voltage/frequency fluctuations and oscillations that typically occur on the grid, in particular its stalling conditions. Additionally, it will provide an understanding of the characteristics of these A/C’s in steady-state; such as the harmonic distortion levels and electrical protection and controls. The test data is needed to build, test, and/or validate 3-Φ A/C model for dynamic, steady-state, and harmonic performance. A supplemental intent of this testing is to find out if these A/C’s are “grid friendly” devices and/or what is needed to remedy any potential impacts to the electric power system. A/C performance data is needed for validation of power system simulation models used for power system planning studies. The inadequacy of residential load models became evident when Southern California Edison (SCE) and other utilities in the US, and other countries, experienced several delayed voltage recovery events after transmission or sub transmission fault clearing. The most significant occurrence of this event in the SCE system took place on August 5, 1997. During the fault, the system voltage dropped below 60% causing many residential air conditioner compressor motors in the system to stall, increasing the VAR demand, and delaying the voltage recovery. The model used for the simulation of the August 5 event was more optimistic than the measured event data (i.e. the simulation showed a slightly faster recovery than the measured event data).