Carrier 69NT40-511-199, 69NT40-521 manual Cooling in Low Speed with Two-Speed Compressor See Figure

b.Cooling in Low Speed with Two-Speed Compressor (See Figure 4-2.)

NOTE

Evaporator fan motors will run in high speed. (Contactor EF energized)

NOTE

A pressure control system has been incorporated by means of a condenser pressure transducer (CPT) and condenser pressure control (CPC) logic to maintain discharge pressures above 130 psig in low ambients.

The condenser fan will cycle off if the condenser pressure is below 130 psig. If the condenser pressure goes above 200 psig, the condenser fan will cycle on.

With supply air temperature decreasing, and if the supply air is above set point, the unit will be cooling with the condenser fan motor, compressor motor and evaporator fan motors energized. Also, at this time, the cool light is illuminated.

When the air temperature decreases to a predetermined tolerance above set point, relay TI energizes and the in-range light is illuminated.

(Refer to section 3.1.4, Code 30.)

If the air temperature continues to fall, modulating cooling starts at approximately 2.5_C (4.5_F) above set

point. The modulating valve will have a variable current up to 1.30 amps at full modulation.

During this cooling mode, a running sum of the temperature differential (supply air temperature - set point) is kept. When the supply air falls below set point, the differential is negative. The longer supply air remains below set point, the greater the negative differential in the running sum.

When the supply air temperature decreases to 0.2_C below set point and the running sum is less than -250 degrees C-seconds, relays TN and TC de-energize shutting off the condenser fan and compressor motors. Also, the cool light is de-energized.

The evaporator fan motors continue to run to circulate air throughout the container. The in-range light remains illuminated as long as the supply air is within a tolerance of set point, and the 15 minute override is met.

If the unit is in the holding mode (neither heating nor cooling) and the supply air temperature increases to 0.2_C (0.4_F) above set point, and providing a six minute off time has elapsed, relay TC energizes to restart the compressor. Also, at this time, the condenser fan motor starts and the cool light is illuminated.

During this mode the two-speed compressor can be either running in high or low speed depending on the box load, ambient temperature, time since power-on, AC line voltage and the position of the SSV.

T-268-07 4-6