Carrier MMY-MAP0724FT9UL Service Manual page 66

NO. Item
9
High pressure This control function is aimed at automatically shutting down a compressor in an
release outdoor unit depending on Pd pressure. It is individually performed by the header
compressor unit and each follower unit.
shutdown
1) Control details
control
10 Case heater There are two types of case heaters: a compressor case heater and an
control accumulator case heater. This control function is aimed at preventing the
accumulation of refrigerant in those cases, and is performed by all outdoor units.
If the power supply has not been turned on for a specified period before a
postinstallation test run, compressor failure may occur. Similarly, when starting
compressors after a long period of no power supply, it is recommended that the
power supply be turned on for a while before operation is resumed, just like a post-
installation test run.
This control function is sometimes used alongside an electrical charging of the
compressor motor windings. In this case, a charging sound may be heard, but this
is normal.
1) Control details
Specification outline
• Compressors are shut down when Pd pressure reaches or exceeds P0.
• The compressor restart prevention timer (2 minutes 30 seconds) is set, and
the control terminated.
• The heaters are turned on while the compressors are turned off.
• The heaters are turned off when To sensor temperature becomes ≥ 82.4°F
(28°C), and are turned back on when To sensor temperature becomes ≤
77°F (25°C).
• When the compressors are turned on, the heaters are kept on for 10
minutes.
– 66 –
Remarks
• When Pd ≥ P0 =
500 psi (3.45 MPa),
compressor No. 2 or
No. 3 (the last one of
three compressors in
terms of startup
order in a three
compressor
configuration) is shut
down.
• When Pd ≥ P0 =
508 psi (3.5 MPa),
compressor No. 1
(the first compressor
in terms of startup
order) is shut down.