Thermo King 002008, Manual

Page: 22 / 155

Unit Description
22
System Operation
Several operating characteristics of the unit are:
• All zones can cool at the same time.
• All zones can heat at the same time.
• Any zone can cool while any other zone heats.
• When the host zone is in defrost, it may delay
cool or heat in the other zone(s).
• When a zone is in null, the blowers may run
but the zone does not cool or heat.
• When a zone is in heat while another zone is
in cool, the evaporator in the zone that is in
heat acts as the condenser.
• The condenser inlet solenoid and the suction
line solenoids are normally open solenoid
valves that close when energized.
• The liquid line solenoids, the hot gas
solenoids, the receiver tank pressure solenoid
and the purge valve are normally closed
solenoid valves that open when energized.
• The flow of refrigerant through the system is
controlled by the solenoid valves and the
check valves.
• If the condenser inlet solenoid is energized
(closed) because a zone is in heat or defrost,
and if the discharge pressure exceeds 400 psi
(2758 kPa), the condenser inlet solenoid is
de-energized until the discharge pressure
drops below 250 psi (1724 kPa).
• The receiver tank pressure solenoid and the
purge valve are energized (open) when any
zone is in heat or defrost. If the discharge
pressure exceeds 300 psi (2068 kPa), the
receiver tank pressure solenoid and the purge
valve are de-energized until the discharge
pressure drops below 225 psi (1551 kPa).
• During engine operation when all zones are in
cool, the microprocessor will shift the engine
to low speed if the discharge pressure exceeds
425 psi (2930 kPa). High speed is enabled, if
required, when the discharge pressure drops
below 375 psi (2586 kPa).
• During engine operation when all zones are in
heat, the microprocessor will shift the engine
to low speed if the discharge pressure exceeds
375 psi (2586 kPa). High speed is enabled, if
required, when the discharge pressure drops
below 300 psi (2068 kPa).