Appendix F - Optional Low Ambient; Motormaster V Control - United Technologies Carrier Weathermaker 48A2 Controls, Start-Up, Operation, Service, And Troubleshooting

APPENDIX F — OPTIONAL LOW AMBIENT MOTORMASTER
This appendix contains instructions for the start-up and ser-
vice of the optional low ambient Motormaster
trol 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 shall be managed
directly by the ComfortLink controls (no third party control).
The head pressure control stages fixed speed fans and mod-
ulating fans, if available, to maintain the head pressures of cir-
cuit A and circuit B within acceptable ranges. For controls pur-
pose, the head pressures are converted to saturated condensing
temperatures (SCTs) as the feedback information to the con-
denser fans (also referred to as 'outdoor fans'). SCT.A is the sat-
urated condensing temperature for refrigeration Circuit A, and
Fig. M — Low Ambient MMV Control Location — 48/50A020-035 Units
SCT.B is the saturated condensing temperature for refrigeration
® V (MMV) con- Circuit B. There are a total of up to 6 condenser fans (depend-
ing on unit size and installed options) for controlling the head
pressures of the 2 refrigeration circuits, of which up to 2 fans
can be controlled by VFD(s) (variable frequency drive(s)) upon
installation option.
condenser fan control. Where Motormaster control is involved,
it may also referred to as low ambient control.
plemented in the ComfortLink software. It shall not be compat-
ible with the existing Motormaster V control as found in
CESR131343-07-xx and earlier that make use of accessory
part
CRLOWAMB026A00.
190
®
V CONTROL
The control described in this document is also referred to as
The low ambient control described here shall be directly im-
numbers CRLOWAMB018A00
Location of Motormaster V device is shown in Fig. M-P.
through