Ambient Control - Carrier WeatherMaker 48A2020 Controls, Start-Up, Operation, Service And Troubleshooting Instructions

APPENDIX G — OPTIONAL GREENSPEED
This appendix contains instructions for the start-up and service
of the optional Greenspeed/low ambient control on 48/
50A020-060 units. For Design Series number (the 13th digit of
the model number) less than 4 unit with legacy Motormaster
VFD, please refer to Appendix F.
The Greenspeed/low ambient Option utilizes varied frequency
drives (VFDs) which adjust condenser fan motor speed in re-
sponse to varying saturated refrigerant head pressure. A prop-
erly applied Greenspeed/low ambient Option control extends
the operating range of air-conditioning systems and permits
operation at lower outdoor ambient temperatures. Head pres-
sure refers to the refrigerant pressure at the discharge side of
the compressor. Thus it is sometimes refers to as 'discharge
pressure'. Head pressure control will be managed directly by
the ComfortLink controls (no third party control).
The head pressure control stages fixed speed fans and modulating
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 temperatures
Fig. R — Greenspeed/Low Ambient VFD Control Location — 48/50A020-035 Units
®
/LOW AMBIENT CONTROL
(SCTs) as the feedback information to the condenser fans (also re-
ferred 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 Circuit B. There are a to-
tal of up to 6 condenser fans (depending on unit size and installed
options) for controlling the head pressures of the 2 refrigeration
circuits. The Greenspeed Option can further optimize the energy
efficiency of the units by varying the speeds of condenser fans to
achieve optimal head pressures during normal operations.
The control described in this document is also referred to as
condenser fan control.
The low ambient control described here will be directly imple-
mented in the ComfortLink software. It will not be compatible
with the existing Motormaster V control as found in
CESR131343-07-xx and earlier that make use of accessory part
numbers CRLOWAMB018A00 through CRLOWAMB026A00.
The location of Greenspeed/low ambient VFD device is shown
in Fig. R-T.
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