Heat Sinks, or HS's, dissipate the heat generated by JJs, movement, and weapons. The more Heat Sinks an asset has, the faster it cools. Having more Heat Sinks does not increase maximum heat capacity, it only improves cooling rate.
There are two kinds of heat sinks: Single heat sinks (HS) and Double heat sinks (DHS). A double heat sink dissipates heat twice as fast as a single heat sink, while single heat sinks have more health and are harder to destroy from overheating.
Single heat sinks are usually found on certain Inner Sphere 'Mechs. All vehicles in MWLL use single heat sinks as well. Otherwise, all other assets have double heat sinks.
Heat Sinks work more quickly when in water, when Powered Down, when using coolant, and when the Heat Sinks are at full health. Heat sink damage occurs when overheating over the yellow line.
Using the automatic shutdown override, [H], increases Heat Sink damage when overheating.
Heat sinks operate by collecting heat with coolant distributed to heat sources (weapons, engines, myomers, electronics, etc.) and delivering that to a radiator. Because a BattleMech may operate in environments considerably hotter than the interior of the 'Mech, the system includes a heat pump to "force" the heat out of the 'Mech by elevating the temperature of the coolant in some reversible fashion. (The vapor-compression heat pump of home air conditioners is a typical example, but 31st Century BattleMechs may make use of more exotic heat pumps.) Double Heat Sinks, often abbreviated DHS and colloquially also referred to as Freezers throughout the Inner Sphere after their NAIS codename, operate in much the same way and for the same purpose as standard heat sinks. The difference is that a double heat sink offers twice the heat dissipation capacity of a standard heat sink, for the same mass (one ton). Double Heat Sink technology was originally developed during the Star League Era, but was lost during the Succession Wars. However, thanks to the discovery of the Helm Memory Core twenty-two years before the Clan Invasion, the Inner Sphere managed to recreate the DHS - it took up three times as many slots as a Single Heat Sink. The Clans, having never lost the technology, advanced it to the point where it would only take up two slots.
BattleTech reference Heat Sinks
BattleTech reference Double Heat Sinks