The paper extends the packetized energy management (PEM) control strategy to enable coordination of compressor-based thermostatically controlled loads (TCLs), such as air conditioners. This establishes a new method of harnessing the flexibility of this ubiquitous resource, enabling a variety of grid services, such as frequency regulation. In the original PEM scheme, resources request energy packets and turn on if their request is approved. That PEM scheme has been further extended by introducing the concept of turn-off requests. We find that this increases flexibility and improves tracking performance. Through a case study involving over 1000 air conditioners, we evaluate the performance of a population of TCLs providing frequency regulation under PEM, highlighting both the capabilities and limitations. Simulations indicate our controller extensions significantly increase resource availability and tracking performance. We show that it is possible to achieve RMS tracking error below 2% when providing more than 250 kW of frequency regulation.