A trailer refrigeration unit comprising: a plurality of power sources (102, 104, 108), wherein the plurality of power sources are selectively coupled to a power converter and at least one compressor; and wherein the power converter is coupled to at least one fan; and a first switch configured to selectively couple the power converter to the plurality of power sources; and a second switch configured to selectively couple the power converter to the at least one compressor; and a microcontroller circuit, wherein the microcontroller circuit is configured to: selectively operate the trailer refrigeration unit in one of a plurality of modes based on an environmental parameter within the trailer refrigeration unit, wherein the plurality of modes includes: a first mode where the at least one compressor is directly powered by at least one of the plurality of power sources (102, 104, 108) such that power is routed to the compressor from a power source other than the power converter, in which the microcontroller circuit is configured to utilize the first switch and the second switch to control a pull down to come from one of the plurality of power sources, and a second mode where the at least one compressor and at least one fan are powered by the power converter, in which the microcontroller circuit is configured to utilize the second switch to route power to the at least one compressor through the power converter. a plurality of power sources (102, 104, 108), wherein the plurality of power sources are selectively coupled to a power converter and at least one compressor; and wherein the power converter is coupled to at least one fan; and a first switch configured to selectively couple the power converter to the plurality of power sources; and a second switch configured to selectively couple the power converter to the at least one compressor; and a microcontroller circuit, wherein the microcontroller circuit is configured to: selectively operate the trailer refrigeration unit in one of a plurality of modes based on an environmental parameter within the trailer refrigeration unit, wherein the plurality of modes includes: a first mode where the at least one compressor is directly powered by at least one of the plurality of power sources (102, 104, 108) such that power is routed to the compressor from a power source other than the power converter, in which the microcontroller circuit is configured to utilize the first switch and the second switch to control a pull down to come from one of the plurality of power sources, and a second mode where the at least one compressor and at least one fan are powered by the power converter, in which the microcontroller circuit is configured to utilize the second switch to route power to the at least one compressor through the power converter. a first mode where the at least one compressor is directly powered by at least one of the plurality of power sources (102, 104, 108) such that power is routed to the compressor from a power source other than the power converter, in which the microcontroller circuit is configured to utilize the first switch and the second switch to control a pull down to come from one of the plurality of power sources, and a second mode where the at least one compressor and at least one fan are powered by the power converter, in which the microcontroller circuit is configured to utilize the second switch to route power to the at least one compressor through the power converter.