Latent Heat- Heat that when added to or removed from a substance causes a change of state but not a change in temperature.

Latent Heat of Evaporation - The amount of heat added to a substance during the change of state.

Lag of temperature control - The delay in action of a temperature element due to the time required for the temperature of the element to reach the medium temperature.

Leak Detector - A device to locate refrigerant leaks.

Liquid Line - The line that caries the high temperature high pressure sub cooled liquid from the receiver  line to the metering device.

Liquid Receiver - A device used to store refrigerant till it is required.

Liquid-to-Air  - A system which absorbs heat from a liquid and rejects it to the air.

Liquid-to-Liquid heat pump - A heat pump which absorbs heat from a liquid and also rejects it to a liquid.

Load - The required rate of heat removal.

Low side - The area of the refrigeration cycle that operates under a lower pressure compared to the high side.