This paper describes an air-conditioner (A/C) compressor single phase induction motor (SPIM) model for use in an electro-magnetic transients (EMTs) simulation. The system of differential equations representing the SPIM model is developed and formulated. The angular position of the rotor shaft is retained in the electrical and mechanical equations of the model so that position dependence of the driven-load torque can be explicitly recognized. The equivalent circuit of the proposed model is represented as an interface to the external electric network in the EMTs simulator. Motor dynamic response to voltage dip at different points on the voltage waveform has been studied. The rationale of motor stalling is explored. Multiple aggregate units of the proposed model have been implemented on a distribution feeder to test and verify the motor dynamics in an EMTs simulation.