SiUS331604E Outline of Control (Indoor Unit)
Functions and Control 64
6.9 Freeze-up Prevention
Freeze-up Prevention by Off Cycle (Indoor Unit Individual Control)
When the temperature detected by the liquid pipe temperature thermistor of the indoor heat exchanger drops too
low, the unit enters freeze-up prevention control in accordance with the following conditions, and is also set in
accordance with the conditions given below. (Thermostat OFF)
When freeze-up prevention is activated, the electronic expansion valve is closed, the drain pump turns on and
the airflow rate is fixed to L tap. When the following conditions for cancelling are satisfied, it will reset.
Conditions for starting:
Liquid pipe temperature ≤ – 1°C (30.2°F) (for total of 40 minutes)
or
Liquid pipe temperature ≤ – 5°C (23°F) (for total of 10 minutes)
Condition for cancelling:
Liquid pipe temperature ≥ +7°C (44.6°F) (for 10 minutes continuously)
The idea of freeze-up prevention control
Difficult to carry out freeze-up prevention operation
· For comfort, suppression of frequent thermostat ON/OFF is necessary.
· Suppressing the switching frequency of the compressor is required to ensure reliability.
After freeze-up prevention operation is carried out, the compressor can be defrosted properly.
· Water leakage prevention must be effective.
Normal operation
Start
Cancel
Liquid pipe
temperature
Start
Cancel
Normal operation
–5ºC
(23˚F)
0ºC
(32˚F)
+7ºC
(44.6˚F)
–1ºC
(30.2˚F)
t1 t2 t3 t4
0ºC
(32˚F)
+7ºC
(44.6˚F)
10 min.
OR
10 min.
10 min.
t > 40 minutes
Freeze-up prevention control
Forced OFF by thermostat
Freeze-up prevention control
Forced OFF by thermostat
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