Coolers　are　critical　components　in　various　industrial　systems,　which　can　effectively　mitigate　temperature-induced　failure　risks.　In　this　paper,　we　investigate　the　reliability　analysis　and　maintenance　optimization　approaches　of　a　two-unit　warm　standby　cooling　equipment.　The　working　conditions　of　both　coolers　have　significant　influence　on　the　temperature　variation　of　the　target　system.　When　at　least　one　cooler　is　working　normally,　the　temperature　rises　slowly　(represented　by　a　small　degradation　rate);　otherwise　the　temperature　rises　sharply　(represented　by　a　relatively　large　degradation　rate).　We　use　a　multi-stage　Wiener　process　to　characterize　the　degradation　trend　of　the　system.　The　reliability　function　of　the　system　is　formulated,　and　accordingly　a　condition-based　maintenance　policy　is　developed　based　on　temperature　monitoring　information.　The　maintenance　cost　is　minimized　via　the　joint　optimization　of　the　temperature　control　limit　and　age　threshold.　A　case　study　of　an　enclosed　busbar　with　two　coolers　is　given　to　illustrate　the　application　of　the　proposed　model.