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