Carrier 69NT20-531-300 manual Controller Operation -- Frozen Mode

FALLING

TEMPERATURE

START UNLOADED,

TRANSITION TO

ECONOMIZED

OPERATION

AIR CIRCULATION

RISING

TEMPERATURE

COOLING

ECONOMIZED

+.20_C

SET POINT

--0.20_C

AIR CIRCULATION

NOTE: TEMPERATURES INDICATIONS ARE ABOVE OR BELOW SET POINT

Figure 4-3 Controller Operation -- Frozen Mode

ENERGIZED
DE--ENERGIZED	CONTROL TRANSFORMER
FOR FULL DIAGRAM AND
LEGEND, SEE SECTION 7

POWER TO
CONTROLLER
T6	PB		PA
TD	T6	PA	PB
SIGNAL TO
CONTROLLER	TU	USV
TS			ESV

NOTE: HIGH SPEED EVAPORATOR FAN SHOWN. FOR LOW SPEED CONTACT TE IS DE--ENERGIZED AND CONTACT TV IS ENERGIZED

Figure 4-4 Perishable Mode

4.9.1Sequence Of operation -- Compressor Phase Sequence

The controller logic will check for proper compressor rotation. If the compressor is rotating in the wrong direction, the controller will energize or de-energize relay T6 as required (see Figure 4-4). Energizing relay T6 will switch operation from compressor contactor PA to compressor contactor PB. De-energizing relay T6

will switch operation from compressor contactor PB to compressor contactor PA. Compressor contactors PA is wired to run the compressor on L1, L2, and L3. Compressor contactor PB is wired to run the compressor on L2, L1 and L3 thus providing reverse rotation .

4.9.2Sequence Of Operation -- Perishable Mode Cooling

NOTE

In the Conventional Perishable Mode of opera- tion the evaporator motors run in high speed. In the Economy Perishable Mode the fan speed is varied.

a. With supply air temperature above set point and de- creasing, the unit will be cooling with the condenser fan motor (CF), compressor motor (PA or PB), evap- orator fan motors (EF) energized and the COOL light illuminated. (See Figure 4-4.) Also, if current or pressure limiting is not active, the controller will en- ergize relay TS to open the economizer solenoid valve (ESV) and place the unit in economized opera- tion.

b. When the air temperature decreases to a predeter- mined tolerance above set point, the in-range light is illuminated.

c. As the air temperature continues to fall, modulating cooling starts at approximately 2.5_C (4.5_F) above set point. (See Figure 4-2.) At set point, relay TS is de-energized to close the economizer solenoid valve and relay TU is energized to open the unolader sole-

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