Daikin FH35BZV1 [227/397] Motor operated valve control

ESiEN02–01A Overview of the heating mode functions

Part 2 – Functional Description 2–49

3.9 Motor Operated Valve Control

Applicable units R(Y)P71-250B

Pump down

residual operation

The unit conducts a pump down residual operation after each compressor stop command. The

purpose of this function is to collect the refrigerant in the liquid receiver in order to prevent refrigerant

from remaining in the indoor heat exchanger.

Start-up control When the compressor starts, a pump down operation is carried out in order to avoid liquid pumping.

The liquid receiver fills up and a minimum refrigerant amount is passed to the compressor. This

minimum refrigerant amount is required to avoid discharge pipe temperatures that are too high.

The opening degree of the expansion valve depends on the start-up number. If the first start-up fails,

the opening degree of the following start-up is adapted by the self-learning function.

Initial opening

degree

The initial opening degree of the outdoor expansion valve depends on the indoor and outdoor air

temperature. The calculation of the opening degree is made at a thermostat ON and at the end of a

defrosting cycle.

Opening degree:

Self-learning

function

When the system was stopped due to abnormal suction or discharge pressure, or due to a discharge

temperature that is too high, the expansion valve control tries to avoid the same breakdown. The

expansion valve increases the previous opening degree with 70 (in cooling mode) or 80 (in heating

mode) pulses at the next start-up.

There are maximum five start-up attempts. When the compressor stops again after the fifth start-up,

something is wrong with the unit and a unit check is necessary. The relevant error code appears on

the remote control.

Compressor

OFF

Thermostat

Refrigerant

recuperation

480

OFF

Compressor

OFF

Thermostat

1. Equalisation

2. Start-up control

3. Normal control

123

480

OFF