A trailer refrigeration unit comprising: a plurality of power sources , 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 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 , 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 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 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 . <EOS>