I have an older Carrier Infinity HVAC system. The thermostat communicates with the compressor and air handler on a simple digital network. The digital controller on the air handler then communicates with the blower motor controller to provide run signals and return some basic motor run status. I have had the motor control module go out a couple times, I think related to power droops and or lightning strikes. Fortunately, I have been able to diagnose the problem and get replacements off Ebay. The motor appears to be a 3-phase permanent magnet motor with no feedback, pictured below. Anyway my question, do any of you know the signaling to one of these? Based on the simplicity, just TX and RX to the motor controller, I'm guessing its just a PWM signal for three different speeds and a returned pulse train indicating activity. I could probably cobble up a break out connector and drag my scope under the house to check, but that would be messy.