installation instructions

installation instructions
548D/549B
ACCESSORY MOTORMASTERT IV
HEAD PRESSURE CONTROLLER
PART NUMBER 389034-202
551B/558D/
580D/581B
Cancels: New
Sizes 036-120
Sizes 036-150
IIK 548-36-32
3/15/99
SAFETY CONSIDERATIONS
Installation, start-up, and servicing of this equipment can be
hazardous due to system pressures, electrical components, and
equipment location (roofs, elevated structures, etc.)
Only trained, qualified installers and service technicians should
install, start up, and service this equipment.
When working on this equipment, observe precautions in the
literature, tags, stickers, and labels attached to the equipment, and any other safety precautions that may apply.
WARNING: Open all remote disconnects before
servicing this equipment. Electrical shock could result
in personal injury.
INTRODUCTION
The Motormaster IV Head Pressure Controller is a cycle control device activated by a pressure sensor mounted on the
Schrader port of the liquid line (see Fig. 1). It is designed to
cycle the outdoor-fan motors to maintain the saturated condensing temperature within normal operating limits of approximately 110 F (high) and 60 F (low). The compressor
maintains working head pressure at low ambient temperatures down to −20 F.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
INSTALLATION
Disconnect power to unit.
Disconnect outdoor-fan motor (OFM) wires at the
contactor (21).
Securely connect pressure switch flare nut (on pressure switch assembly) to either male flare fitting on
adapter tee provided in kit (see Fig. 2). Be sure to use
a flare gasket (provided in the kit.)
Locate service fitting on tube. Remove cap from service fitting and place on remaining male flare fitting on
adapter tee.
Securely connect female flare nut on adapter tee to service fitting. Be sure to use a flare gasket (provided in
the kit).
Check all refrigerant connections for leaks, repair if
necessary.
Connect OFM wire to one lead of pressure switch using a crimp connector or wire nut (see Fig. 3).
Connect other lead of pressure switch to T1 (21) at the
unit contactor, securing excess wire.
If installing on a Heat Pump, you must add a relay
24-volt coil (normally closed) and wire per Fig. 3.
Reconnect power to unit.
FLARE NUT ON
PRESSURE SWITCH
Fig. 1 — Motormaster IV Head Pressure Controller
Fig. 2 — High- and Low-Pressure Switch
Refrigerant Connections
OFM
CONTACTOR
HN61KJ250
YEL
23
13
BLK
21
11
R1
BLK
BLK
OF1
OF2
O
C
LOW
VOLTAGE
TERMINALS
DEFROST
CONTROL
BOARD
LEGEND
OFM — Outdoor-Fan Motor
Aux Wiring for Heat Pump
R1
HN61KJ250 or Equivalent
389034-202 Pressure Switch
Fig. 3 — Wiring Schematic — 548D/549B/551B/558D/580D/581B
Copyright 1999 Bryant Heating & Cooling Systems
CATALOG NO. 5354-803