Carrier MMY-MAP0724FT9UL Service Manual page 63

NO. Item
5
Oil equation This control function is aimed at preventing compressors from running out of oil by
control evening out the oil supply to outdoor units, and is basically performed by opening/
closing solenoid valves SV3A, SV3B, SV3C, SV3D, and SV3F. There are three control
patterns as described below. (For a schematic diagram of oil equalization control, see
4. Oil level detection control in the previous page.)
1. Preparatory control
If the oil level judgment result in the memory continues to be "low" for 30 seconds,
SV3B is turned on, with SV3D turned on and off intermittently.
2. Oil equation control
This control function is performed to transfer oil to the outdoor unit whose oil level
is low from other outdoor units. It takes place whenever the header unit registers a
low oil level result while at least one of its compressors is turned on or at least one
of the follower units issues an oil level equation request.
This control function does not apply to a header unit-only system (no follower units
connected).
3. Oil depletion protection control
This control function is performed if oil equation control fails to achieve an optimum oil
level. In concrete terms, if a low oil level situation continues for 30 minutes, the unit is
brought to a protective shutdown, followed by a restart 2 minutes and 30 seconds later.
If protective shutdown is repeated three times, the error is confirmed as final.
(There will be no more restarts.) The error code is "H07".
6
Refrigerant/ 1. Cooling oil (refrigerant) recovery control
oil recovery
Performed during all cooling or mainly cooling operation, this control function aims
control
to: periodically collect any refrigerating oil condensate that has built up in inter-unit
gas pipes and indoor units and return it to outdoor units when the compressor
operation command is inadequate; and prevent the accumulation of refrigerant in
outdoor heat exchangers while cooling operation is in progress under low outside
air temperature conditions.
It is managed by the header outdoor unit.
1) Control commencement conditions
2) Control details
2. Heating refrigerant (oil) recovery control
Performed during all heating or mainly heating operation, this control function aims
to recover any liquid refrigerant trapped inside indoor units that have been turned
off. It also serves the additional purposes of recovering indoor/outdoor refrigerant
after defrosting and recovering oil present in outdoor heat exchangers during
heating overload operation.
This control function is managed by the header outdoor unit.
1) Control commencement conditions
2) Control details
3. Cooling oil recovery control at mainly operation
This control is provided to recover the refrigerator oil which stagnates in the low-pressure
gas inter-unit piping at simultaneous operation (regardless of cooling or heating).
1) Control condition (Representative)
2) Control contents
Specification outline
• When cooling operation has continued for at least 2 hours
• When cooling operation has started (compressors have just been turned on,
though this does not always happen depending on outside air temperature
conditions).
• All compressors currently in operation are operated at the minimum speed,
with those currently not in operation turned on.
• Indoor units are set to the cooling oil (refrigerant) recovery control mode, with
their indoor PMVs opened to a certain degree.
• Compressors are operated at the target speed.
• After recovery control is performed for a specified period of time, it is
terminated, and normal cooling operation resumes.
• When heating operation has started (compressors have just been turned on)
• When heating takes over upon completion of defrosting
• When heating operation has continued for 60 minutes
• All compressors currently in operation are operated at the minimum speed,
with those currently not in operation turned on.
• Indoor units are set to the heating refrigerant (oil) recovery control mode, with
their indoor PMVs opened to a certain degree.
• Compressors are operated at the target speed.
• Upon completion of refrigerant recovery for all the indoor units, normal cooling
operation resumes.
• When integrating time of compressor ON reached to 95 minutes during
simultaneous operation
When the conditions are satisfied, set cooling operation to heating indoor unit temporarily
(stop the indoor fan) and then recover oil for 2 minutes 30 seconds to max. 10 minutes.
The cooling indoor unit continues operation.
– 63 –
Remarks
• Oil accumulated
in the oil
separator is
returned to the
compressor.
• This is normal oil
equalization
control.
• This protective
control is
performed when a
prolonged low oil
level is detected.
• Cooling oil
recovery control
takes place
approximately
every 2 hours.
• Control duration
is about 2 to 5
minutes, though it
varies according
to the operating
conditions of the
system.
• Heating oil
recovery control
takes place
approximately
every hour.
• Control duration
is about 2 to 10
minutes, though it
varies according
to loading
conditions.
• Compressor
rotational speed
varies with control
conditions, indoor
unit capacity, and
outdoor unit
specification.