Heat Pump Operation

Crankcase Heater

This item is “ON” whenever power is supplied to the unit and the crankcase heater thermostat is closed. Crankcase heater thermostat closes at 67° and opens at 85°. It warms the compressor crankcase thereby preventing liquid migration and subsequent compressor damage. The insert type heater is self regulating. It is connected electrically to the contactor L1 and L2 terminals.

Condenser Motor

This item is activated by the contactor during heating and cooling, except during defrost and emergency heat operation.

Compressor

This item is activated by the contactor for heating and cooling, except during emergency heat. It is protected by an internal over- load.

Contactor Relay

This control is activated by the thermostat (24V coil) and supplies power to the contactor.

Defrost Control

The Defrost control provides time/temperature initiation and termi- nation of the defrost cycle. When a Defrost cycle is initiated, the defrost control shifts the reversing valve to “COOLING” mode, stops the outdoor fan and brings on supplemental heat. Normally, a Defrost cycle will take only 2-3 minutes unless system is low on charge or outdoor conditions are severe. (windy and cold). The defrost control also provides for a 3 minute off cycle compressor delay.

Outdoor Thermostat

These optional controls are used to prevent full electric heater operation at varying outdoor ambient (0° F-to 45° F). They are nor- mally open above their set points and closed below to permit stag- ing of indoor supplement heater operation. If the outdoor ambient temperature is below 0° F (-18° C) with 50% or higher RH, an outdoor thermostat (OT) must be installed and set at (0°) on the dial. Failure to comply with this requirement may result in damage to the product which may not be covered by the manufacturer’s

HEATING CYCLE

The heat pump operates in the heating cycle by redirecting refrig- erant flow through the refrigerant circuit external to the compres- sor. This is accomplished with through the reversing valve. Hot discharge vapor from the compressor is directed to the indoor coil (evaporator on the cooling cycle) where the heat is removed, and the vapor condenses to liquid. It then goes through the expansion device to the outdoor coil (condenser on the cooling cycle) where the liquid is evaporated, and the vapor goes to the compressor.

CO OLING

	SERVIC E PO RT			REVERSING VALVE
	SERV IC E VA LVE
	SERVIC E PO RT	ACCUM ULATO R
	CO MPRESSOR
EVAPORATOR	DIST RIBU TOR			CONDENSER
EVAPORATOR	EXPANSION DEV IC E	SERVIC E PO RT		CONDENSER
	EXPANSION DEV IC E

	CHECK VALVE		CH ECK VALVE
INDO OR	OR IFICE SERVIC E		O RIFICE	O U TDO OR
CO IL	VALV E			CO IL
H EATIN G
	SERVIC E PO RT			REVERSING VALVE

SERVIC E VALVE

AC CUM ULATO R

warranty.

Reversing Valve Coil

This coil is activated by the thermostat, in the cooling mode and during defrost. It positions the reversing valve pilot valve for cooling operation.

Indoor Blower Motor

This is activated by the room thermostat by COOLING or FAN ON position. The motor is energized through the EBTDR for PSC mo-

CONDENSER

INDO O R

CO IL

CO MPR ESS OR

DISTRIBU TO R	DISTRIBU TOR
	DISTRIBU TOR
	SERV IC E PO RT
CH ECK VALVE	CH ECK VALVE
O RIFICE SERVICE	OR IF ICE
VALVE

EVAPORATOR

OU TDO OR

CO IL

tors and directly by the room thermostat for X-13 motors (4 or 5 Ton units). X-13 motors are constant torque motors with very low power consumption. This motor is energized by a 24V signal from the thermostat. (See Air Flow Measurement and Adjustment for speed adjustment instructions).

Blower Interlock Relay (Single Phase PSC Models Only)

This relay is used to energize the blower during the electric heat operation. Some room thermostats do not energize the motor dur- ing electric heat. This relay insures blower operation when the room thermostat energizes heat. This relay has a 240 volt coil and an 8 amp contact relay. This relay is energized by the electric heat kit sequencer.

COOLING CYCLE

When the heat pump is in the cooling cycle, it operates exactly as a Summer Air Conditioner unit. In this mode, all the charts and data for service that apply to summer air conditioning apply to the heat pump. Most apply on the heating cycle except that “condenser” becomes “evaporator”, “evaporator” becomes “condenser”, “cool- ing” becomes “heating”.

When the solenoid valve coil is operated either from heating to cooling or vice versa, the piston in the reversing valve to the low pressure (high pressure) reverse positions in the reversing valve. The following figures show a schematic of a heat pump on the cool- ing cycle and the heating cycle. In addition to a reversing valve, a heat pump is equipped with an expansion device and check valve for the indoor coil, and similar equipment for the outdoor coil. It is also provided with a defrost control system.

The expansion devices are flowrator distributors and perform the same function on the heating cycle as on the cooling cycle. The flowrator distributors also act as check valves to allow for the re- verse of refrigerant flow.

When the heat pump is on the heating cycle, the outdoor coil is functioning as an evaporator. The temperature of the refrigerant in the outdoor coil must be below the temperature of the outdoor air in order to extract heat from the air. Thus, the greater the difference in the outdoor temperature and the outdoor coil temperature, the greater the heating capacity of the heat pump. This phenomenon is a characteristic of a heat pump. It is a good practice to provide