Heat Defrosting Control; Discharge Temperature Protection Control; Refrigerant Recovery Control On Heating - Mitsubishi Electric MSC-GE-VB Service Manual

3-4. HEAT DEFROSTING CONTROL

(1) Starting conditions of defrosting
When the following conditions a) ~ c) are satisfied, the defrosting starts.
a) The defrost thermistor reads -2.3°C or less.
b) The cumulative operation time of the compressor has reached any of the set values (31, 35, 45, 55, 65, 75, 85, 95,
105, 115, 150 minutes).
c) More than 5 minutes have passed since the start-up of the compressor.
Set value of compressor operation time (hereinafter referred to as defrost interval)
This is decided by the temperature of defrost thermistor and ambient temperature thermistor, the previous defrosting
time. For example, the first defrost interval is 40 minutes long, and the second is 45 minutes long. The third and sub-
sequent intervals are set to be longer, and less frequent, depending on defrosting time.
The third and subsequent defrost intervals follow any of the three patterns ... 5 or 10 to 20 minutes longer, the same,
or 5 or 10 to 20 minutes shorter compared with the previous defrost interval ... with the longest 125 minutes and the
shortest 40 minutes.
(2) Releasing conditions of defrosting
Defrosting is released when any of the following conditions is satisfied:
a) The defrost thermistor continues to read 10.4°C (MXZ-2B/3B/4B71/3C/4C71)/13°C (MXZ-4B80/5B/4C80/5C/6C).
b) Defrosting time exceeds 10 minutes.
c) Any other mode than HEAT mode is set during defrosting.

3-5. DISCHARGE TEMPERATURE PROTECTION CONTROL

This protection controls the compressor ON/OFF and operation frequency according to temperature of the discharge tem-
perature thermistor.
(1) Compressor ON/OFF
When the temperature of the discharge temperature thermistor exceeds 116°C (MXZ-2B/3B/4B/5B/3C/4C/5C)/114°C
(MXZ-6C) the control stops the compressor.
When the temperature of the discharge temperature thermistor is 80°C (MXZ-2B40/2B52/3B/4B71/3C/4C71)/100°C (MXZ-
2B30/4B80/5B/4C80/5C/6C) or less, the controls start the compressor.
(2) Compressor operation frequency
When the temperature of the discharge temperature thermistor is expected to be higher than 116°C (MXZ-2B/3B/4B/5B/
3C/4C/5C)/113°C (MXZ-6C) the control decreases 12 Hz from the current frequency.
When the temperature of the discharge temperature thermistor is expected to be higher than 111°C and less than 116°C
(MXZ-2B/3B/4B/5B/3C/4C/5C)/113°C (MXZ-6C) the control decreases 6 Hz from the current frequency.
When the temperature of the discharge temperature thermistor is expected to be higher than 104°C and less than 111°C,
the control is set at the current frequency.

3-6. REFRIGERANT RECOVERY CONTROL ON HEATING

MXZ-2B30VA MXZ-2B40VA MXZ-2B52VA
<Control status>
The control performs when the all the following status are satisfied;
• When one or more indoor units are operating in HEAT mode. (Excluding thermostat OFF)
• When the discharge temperature becomes 107°C or more.
• When it passed 60 minutes or more since the operation has started or the last refrigerant recovery has controlled.
<Control details>
LEV opening of indoor unit not operating is controlled to be 80 pulse.
<Control finish status>
The control finishes either as follows. However, the LEV opening is considered to be 59 pulse.
• When it passed 60 seconds since the control has started.
• When the discharge temperature is 90°C or less.
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