Unit installation

June 2013 Application Note 1025
©2013 Mitsubishi Electric US, Inc.
P a g e | 2
Multi-zone (MXZ) heat pump systems can connect two or more indoor units with one outdoor
unit. Be advised that multi-zone systems with model numbers that begin with MXZ do not
support simultaneous heating and cooling. All indoor units on these type models must all be in
the same mode at the same time: either cooling or heating. The entire system will have a mode;
individual indoor units set to the opposite mode will be in standby.
System Mode
The mode of all of the indoor units is determined by the mode of the outdoor unit. The mode of
the outdoor unit is determined by the indoor unit that was operating first. Indoor units set to the
mode opposite of the outdoor unit cannot operate, and the operation indicator lamp flashes to
indicate standby.
Example 1
Consider an MXZ system with two indoor units, IDU-1 and IDU-2, both of which are
initially set to cooling mode. IDU-1 is switched to heating mode. The outdoor unit will
continue to operate in cooling mode until the IDU-2 is switched to heating mode. IDU-2
will still receive cooling to the space, but the IDU-1 will not receive heating to the space.
Instead, the remote controller for IDU-1 will indicate standby mode, or indicator light on
the unit will flash, depending on the model. When IDU-2 is switched to heating mode, the
outdoor unit will switch to heat mode, and both indoor units will receive heating to the
space.
Example 2
Consider an MXZ system with five indoor units, IDU-1, 2, 3, 4,and 5, which are initially in
heating mode. IDU-1, 2, and 3 are switched to cooling mode. The outdoor unit will
continue to stay in heating mode, and IDU-1, 2, and 3 will be in standby. The IDU-1, 2,
and 3 will not receive cooling until IDU-4 and 5 are switched to cooling mode.
IDU-4 is then switched to cooling mode. The outdoor unit will continue to be in heating
mode because that was the last mode in which all indoor units were in the same mode.
When IDU-5 is switched to cooling mode, the outdoor unit will finally switch to cool
mode, and all five indoor units will receive cooling to the space.
Forcing System Changeover
A forced changeover can be achieved by changing all indoor units to the desired mode.
Auto-Mode
Indoor units connected to an MXZ system have three mode options: cool, heat, and auto. It is
recommended that only heat mode and cool mode be used, and not auto mode. Auto mode is
designed for indoor units on one-to-one systems or a VRF simultaneous cooling and heating
systems. Because all of the indoor units on multi-zone MXZ systems must be in the same
Due to continuing improvement, above specification may be subject to change without notice.
2013 P-Series and M-Series - Application Notes (June 2013)
APP-82