13-7
CONTROL SYSTEM
Revision Y05-01Service Manual - DNG Series
13.3.3 OFAN operation
o Min time interval between OFAN ON/OFF state change is 30 sec.
13.3.4 HE operation
o Minimum Heaters ON or OFF time is 30 sec.
o Heaters can be activated only if IFAN is on.
o In RH group, HE-1 and HE-2 will be activated only when COMP (or WVL) is not
operating, except in Dry Mode.
13.3.5 Protections
o High pressure protection is applicable to all operating modes.
o Deicing control is valid in Heat and Auto Heat Mode only.
o Defrosting control is valid in Dry, Cool, Heat and Auto Modes.
o No reset after protection modes.
13.3.6 Thermistors operation
o Return air Temp. is detected by RAT (RT1) in normal Mode, or by RCT (R/C
sensor) in I-FEEL Mode.
o Indoor Coil Temp. is detected by ICT (RT2).
o Outdoor Coil Temp. is detected by OCT (RT3).
o Similarly, in the Indoor Units of a WMQ/T system, 4.7k Ohm (5%) resistors must be
connected to the OCT ports to disable the “Thermistor Temp reading doesn’t
change” error checking.
13.3.7
Definition of thermistor faults:
a. Thermistor is disconnected - The thermistor reading is below -30
o
c.
b. Thermistor is shorted - The thermistor reading is over 75
o
c.
c. Thermistor Temp reading doesn’t change (irrelevant for RT1) -
I.This test is performed only once after a unit is switched from
OFF/STBY to operation. At the first occurrence of 10 min
continuous COMP operation, the current ICT & OCT are compared
with those when the COMP was switched from OFF to ON 10 min
before. If the 'T is less than 3
o
c, the thermistor is regarded as
defective.
II.The ICT and OCT no-change error can be disabled together by
connecting a 4.7 k or 3.9 k ohm resistor (5%) to the OCT
connector. These resistors are equivalent to a thermistor at 43+/-
1
o
c and 48+/-1
o
c respectively.
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