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APPENDIX F — OPTIONAL FACTORY-INSTALLED LOW AMBIENT MOTORMASTER
®
V CONTROL
This appendix contains instructions for the start-up and service
of the optional low ambient Motormaster
®
V (MMV) control
on 48/50A020-060 units.
The Motormaster V control is a motor speed control device
which adjusts condenser fan motor speed in response to vary-
ing liquid refrigerant pressure. A properly applied Motormaster
V control extends the operating range of air-conditioning sys-
tems and permits operation at lower outdoor ambient tempera-
tures. Head pressure refers to the refrigerant pressure at the dis-
charge side of the compressor. Thus it is sometimes refers to as
'discharge pressure'. Head pressure control will be managed di-
rectly by the ComfortLink controls (no third party control).
The head pressure control stages fixed speed fans and modulat-
ing fans, if available, to maintain the head pressures of circuit
A and circuit B within acceptable ranges. For controls purpose,
the head pressures are converted to saturated condensing tem-
peratures (SCTs) as the feedback information to the condenser
fans (also referred to as 'outdoor fans'). SCT.A is the saturated
condensing temperature for refrigeration Circuit A, and SCT.B
is the saturated condensing temperature for refrigeration Cir-
cuit B. There are a total of up to 6 condenser fans (depending
on unit size and installed options) for controlling the head pres-
sures of the 2 refrigeration circuits, of which up to 2 fans can
be controlled by VFD(s) (variable frequency drive(s)) upon in-
stallation option.
The control described in this document is also referred to as
condenser fan control. Where Motormaster control is involved,
it may also referred to as low ambient control.
The low ambient control described here will be directly imple-
mented in the ComfortLink software. It will not be compatible
with the existing field-installed Motormaster V control as found in
CESR131343-07-xx and earlier that make use of accessory part
numbers CRLOWAMB018A00 through CRLOWAMB026A00.
Please refer to page 46 and accessory documentation for those
units with field-installed accessories.
Location of Motormaster V device is shown in Fig. M-P.
Fig. M — Low Ambient MMV Control Location — 48/50A020-035 Units
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