[PDF] AS AN INDICATION OF IMPORTANT SAFETY R-410A HEAT present at the heat pump/defrost control. The heat pump/defrost control will attempt to start unit after the anti-short cycle time expires, when a high or low pressure control automatically resets, or when the heat pump/defrost control exits the lockout mode as the temperature rises above 5°F.[PDF] INSTALLATION INSTRUCTIONS - HVAC heat pump specification sheet should be used. 2.2 APPLICATION Before installing any heat pump equipment, a duct analysis of the structure and a heat gain calculation must be made. A heat gain calculation begins by measuring all external surfaces and openings that gain heat from the surrounding air and quanti-fying that heat gain.