12-5
CONTROL SYSTEM
Revision Y05-01
Service Manual - ALPHA
12.4.5 Protections
•
High pressure protection is applicable to all operating modes.
•
Deicing control is valid in Heat and Auto Heat Mode only.
•
Defrosting control is valid in Dry, Cool, Heat and Auto Modes.
•
No reset after protection modes.
12.4.6 Thermistors
operation
•
Return air Temp. is detected by RAT (RT1) in normal Mode, or by RCT (R/C sensor)
in I-FEEL Mode.
•
Indoor Coil Temp. is detected by ICT (RT2).
12.4.6.1
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 a4.7 kohm resistor (5%) to the OCT connector. These
resistors are equivalent to a thermistor at 43+/-1
o
c and 48+/-1
o
c
respectively.
(iii) Connecting a 4.7k resistor to the ICT connector will disable the
ICT no-change error only.
