The Hoffman Controls 816-10DH Microprocessor Electronic Head Pressure Control modulates (varies) condenser fan motor speed in low ambient temperatures, varying the air volume through the condenser to regulate head pressure. This model’s dual sensor input allows for the control of one or two independent refrigerant circuits sharing the same fan motor(s). Open drip proof, direct drive, PSC or Shaded Pole motors
that are applicable for motor speed regulation must be used. The Controller monitors the liquid line temperature(degrees of excessive sub-cooling) which is directly proportional to the head pressure. Speed modulation begins at 80°F liquid line(65°F ambient temperature) and proportionally reduces the fan to minimum speed once the liquid line temperature reaches 50°F(25°F ambient temperature). Power to the motor is removed at 50°F and below liquid temperatures. At 53°F the fan restarts at full speed; then modulates to minimum speed. When ambient temperatures are at or below approximately 25ºF(50º liquid temperature), the condenser fan motor will cycle between minimum RPM and “off” to maintain proper head pressure. The above describes a 30ºF span (80ºF to 50ºF) function; a 25ºF span is also available. The 25ºF span is recommended for High Efficiency systems; 30º span for typical systems. Variable condenser airflow is modulated from full to minimum speed over the selected span.
The Hoffman Controls 816-10DH purpose is to assure adequate pressure in low ambients:
- a) for maintaining adequate pressure differential for the expansion
- b) assure an adequate pressure to eliminate freezing of the DX coil
for A/C applications,
- c) eliminate oil foaming (oil migration) and/or liquid slugging.
For Heat Pump installations, the Heat Pump input is used to override condenser fan speed regulation. Heat Pump Mode Direct Acting “DA” and Reverse Acting “RA” jumpers are configured based on the manufacturer’s method of energizing or de-energizing the reversing (changeover) valve. Properly configured, the Heat Pump will override speed regulation and allow full speed condenser fan operation when in
the heating mode. The exclusive sensor Range Adjust is provided to optimize the Controller’s performance for specifically, TXV (Thermal Expansion Valves) or Capillary Tube/Orifice systems. The Controller’s 25°F or
30°F span can be adjusted anywhere from 55°F-80°F to 75°-100°F or 50°F–80°F to 70°F–100°F to ensure optimum performance for the specific expansion method. A variable Minimum Speed Adjustment is available to compensate for the bearing type employed by the fan motor. A minimum of 400-RPM for sleeve bearing motors, and 200-RPM for ball bearing motors is recommended. The 816-10DH control does not include a transformer within the controller and will require an external 24VAC transformer.