Units not equipped with a water economizer can be ordered with the reverse/head pressure control valve factory installed and a pressure transducer located in the discharge line of compressor no. 1.
When the condenser water temperature gets low enough to cause the head pressure to drop, the valve will be modulated to control the head pressure of all four compressors by varying the water flow through the condensers.
When the unit is operating and the COOLOK software point is enabled and the EWT gets below 60 F, the Head software point will become enabled and the head pressure control valve will modulate to keep the head pressure at the head pressure set point (SETPT04). The default set point is 225 PSI and may be set from 200 to 250 PSI. The minimum output value for the head pressure control algorithm is 40% in order to maintain a minimum flow through the condensers. The valve will modulate between 40 and 100%. Do not set the minimum lower than 40% or the compressors may shut down due to low flow, resulting in the high-pressure switch tripping.
VENTILATION REQUEST (50XJ) — The ventilation request output will close a set of relay contacts to activate a ventilation damper whenever the supply fan and supply fan status are both true and the TIMECLOCK software point is on.
VAV TERMINAL OPERATION OUTPUT (50XJ) — The VAV terminal control output (TRMCT) closes a set of relay contacts to indicate to non-Carrier air terminals that the fan is either forced on or is going to turn on. This signals the terminals to open and start controlling to the desired CFM and Temperature set points.
VAV TERMINAL OPEN OUTPUT (50XJ) — The VAV ter- minal open output (TRMOP) closes a set of relay contacts to command the air terminals to open to maximum CFM at times when the fan is operating on the VFD Bypass.
PUMP AND TOWER OUTPUTS (50XJ) — The pump and Tower outputs close a set of relay contacts to indicate that the 50XJ unit is in operation and may require condenser water flow through the unit.
BUILDING PRESSURE CONTROL (50XJ) — The building pressure control output provides an analog 4 to 20 mA signal to control return fan or exhaust fan speed. Fan speed is modulated to maintain the building static pressure set point (SETPT07).
The control parameters for the building pressure set point and building pressure are read and controlled in milliamps but are converted to inches of water for ease of setting and display. The range and low start values of the sensor selected should be configured in the custom configurations screen. The raw sensor value in milliamps will be displayed on the hardware point BSP. The converted sensor reading in inches of H2O will be displayed at the software point BSP_IN. The set point input in SETPT07 in inches of H2O is converted to a raw milliamp set point in SETPT08. The algorithm controls to the milliamp values since the math required for control using the static pressure in inches generates numbers too small to be used given the range of the controller configuration parameters.
Diagnostic Features — The CC6400 provides a number of features to help protect the unit and allow problem diagnosis.
CRITICAL FAULT — The controller provides an output (for field connection) to signal an external building systems monitor or control that the unit is not operating properly and has shut down. A red light mounted on the front of the unit provides visual indication of this alarm condition.
NOTE: If the Local/Off/Remote switch is in the OFF position, it is normal for the red alarm light on the display panel to be lit, indicating that the unit is disabled.
NON-CRITICAL FAULT — The controller provides an output for a yellow light, mounted on the front of the unit, that indicates the need for minor maintenance or service.
FIRE INPUT (FSD) — This is a normally closed input, which when opened, deenergizes an isolation relay in the unit, opening the input to the controller. When this input turns On, all control outputs are immediately turned Off, including the fan. Unit reset requires manual resetting at the main controller keypad.
DUCT HIGH STATIC INPUT (DHS) — This air switch provides backup protection for the ductwork. It is factory installed in the unit, wired to the unit main controller to receive 5 vdc. It is a normally open discreet switch, with adjustable manual setting at the switch (range is 1 to 5 in. wg). Upon switch closure, the controller immediately turns all outputs Off, including fan, and then indicates an alarm both by turning On its Alarm Output, Red Alarm light and via communications.
DIRTY FILTERS SWITCH (DFLTS) (50XJ) — This switch measures the change (delta) in air pressure across the filters. When the delta increases beyond the preset setting, a yellow warning light will be lit, indicating that the filters need cleaning or replacement.
The switch receives 5 vdc from the unit controller and monitors air pressure delta across the return air filters. Switch is normally open, with manually adjustable setting at the switch between 0.5 and 1.5 in. wg. Upon closure, controller should wait to assure closure for minimum 1 minute, then indicate an alert via its non-critical alert output and via communications. All other unit operation should remain normal.
COMPRESSOR OVERLOAD (COL)/SAFETIES — Each compressor circuit is provided with a temperature overload board (Copeland Protector Bd.), a Current Overload/Sensor Board (COL), High Pressure Switch (HPS), Low Pressure Switch (LPS), and Evaporator Freeze Switch (EFS). These devices are wired in series to the contactor for each compressor. Each such circuit is then wired through a common resistor board; such that any one or more input(s) to the main controller allows it to discern which compressor is not operating when it should be.
The Current Overload Board (COL) is located in the unit control box, wired in the control power line for the compressor pilot relay (which drives the compressor contactor), and incorporates a current loop which monitors one leg of the compressor power leads. This board is powered along with the related compressor contactor.
Whenever the compressor current falls below a threshold level (i.e., compressor not operating), it activates an on-board relay which opens power to the compressor pilot relay (i.e., compressor contactor), and turns On a control power feedback line to the unit controller, via the resistor board (described above). Any one of the safety switches described herein will cause this event. In the event this occurs, the controller shall turn OFF this compressor, and start the next compressor in sequence. After a 5-minute period, the controller shall restart this compressor, and turn the other one off, as cooling demand requires. If the ‘problem’ compressor then operates for 10 min- utes of run time normally, the unit reverts to normal operation and compressor sequencing. If not, and the same error occurs again, this compressor shall be shut down and replaced with the next compressor, as before, and held off for 10 minutes. It shall then be restarted and the other compressor shut down, as before. If it does not run successfully for 10 minutes of normal run time again, it is shut down and replaced a third time. This time it is held off for 15 minutes. If the “problem” compressor does not operate successfully for the 10 minutes of normal run time this third time, this compressor ONLY is shut down and locked out for servicing. Alarm output (Red light) flashes and then remains on.
HIGH-PRESSURE SWITCH (HPS) — This switch is located in the discharge refrigerant line of each compressor, and is set to open at pressures above 360 psig. It is wired in the 115 vac control power line of the compressor contactor (in series with the LPS and EFS), and activates the COL board (above) when it opens.