Following a failure in side 1 of the HST SI C&DH in September 2008 , HST Servicing Mission 4 ( SM-4 ) was delayed so that a SI C&DH Orbital Replacement Unit ( ORU ) could be qualified for flight . This second generation SI C&DH ( SI C&DH-2 ) included several enhancements which increased its thermal dissipation near critical components . In order to maintain the SI C&DH-2 within its operational temperature limits , several thermal modifications were installed prior to its final qualification testing . This paper presents the thermal modifications performed on the SI C&DH-2 , as well as the thermal ground test results and a correlation of the SI C&DH-2 thermal design to flight telemetry .