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39
OPERATION
Power Up Mode
The unit will not operate until all the inputs, terminals and safety
controls are checked for normal operation.
NOTE: The compressor will have a 5-minute anti-short cycle
upon power up.
Unit Protection Module (UPM)
Figure 24 shows the UPM sequence of operations for unit safeties.
All 50PC units are equipped with a UPM.
Units with Complete C or Deluxe D Controls
STANDBY
Y and W terminals are not active in Standby mode; however, the
O and G terminals may be active, depending on the application.
The compressor will be off.
COOLING
Y and O terminals are active in Cooling mode. After power up, the
first call to the compressor will initiate a 270 to 300 second ran-
dom start delay and a 5-minute anti-short cycle protection time de-
lay. After both delays are complete, the compressor is energized.
NOTE: On all subsequent compressor calls the random start delay
is omitted.
HEATING STAGE 1
Terminal Y is active in heating stage 1. After power up, the first
call to the compressor will initiate a 270 to 300 second random
start delay and a 5-minute anti-short cycle protection time delay.
After both delays are complete, the compressor is energized.
NOTE: On all subsequent compressor calls the random start delay
is omitted.
HOT GAS REHEAT (OPTIONAL)
Terminal H is active in dehumidification mode with hot gas re-
heat. After a call for H, the reversing valve (O), compressor (Y),
and fan (G) are also enabled.
NOTE: Any call for cooling (Y), heating (Y or W), or reversing
valve (O) will override dehumidification mode (H).
WATERSIDE ECONOMIZER (OPTIONAL)
Y and O terminals are active in Cooling mode. When the entering
water temperature drops below the entering water temperature set
point on the waterside economizer aquastat, the compressor and
reversing valve are disabled and the waterside economizer is en-
abled. The waterside economizer three way control valve will di-
vert water to the economizer coil for free cooling. When the enter-
ing water temperature rises above the aquastat set point, the water-
side economizer is disabled and the compressor and reversing
valve are enabled.
TWO WAY WATER
FLOW
CONTROL VALVE
(OPTIONAL)
The two way water flow control valve is enabled anytime there is
a call for cooling (Y), heating (Y), or dehumidification (H) and al-
lows water to flow through the unit. When there is no call for cool-
ing, heating, or dehumidification, the water flow control valve is
disabled, stopping flow through the unit.
BOILERLESS HEAT (DELUXE D ONLY)
When the entering water temperature is below the boilerless heat
aquastat entering water temperature set point and there is a call for
heating (Y), the compressor is disabled and the auxiliary heat out-
put is enabled. When the entering water temperature is above the
aquastat set point, the auxiliary heat output is disabled and the
compressor is enabled.
PUMP/VALVE RELAY (DELUXE D ONLY)
The pump/valve relay is enabled anytime there is a call for cooling
(Y), heating (Y), or dehumidification (H) and can be used to en-
able/disable field installed flow control valves or circulator
pumps. When there is no call for cooling, heating, or dehumidifi-
cation, pump/valve relay is disabled.
Units with WSHP Open Controls
Units with WSHP Open still feature a UPM board for unit opera-
tion, so the operation will be similar to the sequence for the Com-
plete C and Deluxe D package. WSHP Open does feature ad-
vanced functionality, such as automatic fan speed control and in-
telligent alarming, which will differ from the Complete C and
Deluxe D packages. Below is an overview of the different features
for the WSHP Open controls. For more details of the WHSP Open
operation, please refer to the WSHP Open Integration Guide and
the WSHP Points/Properties Manual. See Fig. 25 for WSHP Open
Control Board overview.
COOLING
The control will operate one or two stages of compression to
maintain the desired cooling setpoint. To improve dehumidifica-
tion and reduce noise, the control operates the fan at the lowest
speed possible to satisfy the load conditions. If cooling is active
and should the SAT approach the minimum SAT limit, the fan will
be indexed to the next higher speed. Should this be insufficient
and if the SAT falls further (equal to the minimum SAT limit), the
fan will be indexed to the maximum speed. If the SAT still contin-
ues to falls 5 degrees below the minimum SAT limit, all cooling
stages will be disabled.
During Cooling, the reversing valve output will be held in the
cooling position (either B or O type as configured) even after the
compressor is stopped. The valve will not switch position until the
opposite mode is required.
REVERSE CYCLE HEATING
The control will operate one or two stages of compression to
maintain the desired heating setpoint. To reduce noise, the control
operates the fan at the lowest speed possible. If the heating is ac-
tive and should the SAT approach the maximum SAT limit, the fan
will be indexed to the next higher speed. Should this be insuffi-
cient, then if the SAT rises further and reaches the Maximum
Heating SAT limit, the fan will be indexed to the maximum speed.
If the SAT still continues to rise 5°F above the maximum limit, all
heating stages will be disabled.
During Heating, the reversing valve output will be held in the
heating position (either B or O type as configured) even after the
compressor is stopped. The valve will not switch position until the
opposite mode is required.
TWO POSITION OA DAMPER
The control can be configured to operate a 2-position ventilation
damper to provide the minimum ventilation requirements during
occupied periods.
MODULATING OA DAMPER WITH DCV
The control can be configured to operate a modulating ventilation
damper during occupied periods that responds to changing CO
2
levels from an optional sensor. The control monitors the CO
2
level
and compares it to the configured setpoints and adjusts the ventila-
tion rate as required. The control provides proportional ventilation
to meet the requirements of ASHRAE specifications by providing
a base ventilation rate and then increasing the rate as the CO
2
level
increases. The control has three user adjustable setpoints; start
ventilation maximum ventilation and maximum damper position.
The control will begin to proportionally increase ventilation when
the CO
2
level rises above the start ventilation setpoint and will
reach the full ventilation rate (maximum damper position) when
the CO
2
level is at or above the maximum setpoint. A user config-
urable minimum damper position ensures that proper base ventila-
tion is delivered when occupants are not present.