Sequence of Operation
20
RRU-SVX01F-EN
COOL 1 is activated through RTRM Y1 by the RRUCM
through the COOL 1 R3 Relay when the OAT rises above
the CSP and the Outdoor Air Enthalpy (OE) is below the Y1
– O/Air Dehumid Enable Set Point (OES1). The
Refrigeration Capacity Control (RCC) is enabled when
COOL 1 is active. COOL 2 is disabled during cooling mode.
RCC Operation
The Refrigeration Capacity Control (RCC) monitors
COOL 1 evaporator suction pressure and meters
compressor discharge gas into a de-superheating
chamber where it is mixed with refrigerant introduced
through an integral TXV providing cooling of the hot gas.
Cooled gas is then bypassed to the suction line between
the evaporator and compressor. An integral pressure
controller modulates the quantity of hot gas bypassed to
maintain desired suction pressure-temperature and
prevent frosting indoor coil. The RCC is factory set and
field adjustment is typically not required.
The RCC effectively reduces compressor nominal capacity
and energy consumption when active.
“Occupied” Dehumidification Mode
Call for dehumidification is based on the Outdoor Air
Enthalpy (OE) relative to Y1 – O/Air Dehumid Enable Set
Point (OES1) and Y2 – O/Air Dehumid Enable Set Point
(OES2). Y1 – DEHUMID is activated when the OE is above
OES1.
Y2 – DEHUMID is activated when the OE rises above OES2.
OES1 and OES2 set points are operator adjustable within
a preset range at the ROD. The RCC will operate anytime
the suction pressure drops below the RCC pressure set
point.
Y2 – DEHUMID is deactivated after OE drops 1 Btu below
OES2 set point.
Y1 – DEHUMID is deactivated after OE drops 1 Btu below
OES1 set point.
Hot Gas Reheat (Optional)
Use of this option requires the optional hot gas reheat coil
and requires the operator to INSTALL the HGRH Option at
the ROD.
Call for reheat is controlled by the Supply Air Temperature
(SAT) sensed at the factory mounted Supply Air
Temperature Sensor (STS) located in the supply air
discharge plenum. Reheat is controlled by the operator
adjustable HGRH (Hot Gas Reheat) Control Dead Band
(HGRHD) set point at the RRUCM. On call for reheat, the
RRUCM energizes the Reheat Valve (RHV) through the R5
Relay when the SAT falls below Occupied S/Air Heating
Set Point (HSP) minus HGRHD and is de-energized when
the SAT rises above HSP plus HGRHD.
“Occupied” Heating Mode
Call for heat is based on Outdoor Air Temperature (OAT)
sensed by the Outdoor Air Temperature Sensor (OTS).
When the Supply Air Temperature (SAT) sensed by the
Supply Air Temperature Sensor (STS) drops below the
O/Air Heating Enable Set Point (HESP) a call for HEAT is
initiated by the RRUCM through the R6 HEAT Relay. R6
energizes the Ignition Control Module (IGN) through the
Air Proving Switch (APS) and High Temperature Cutout
(HTC) burner safety circuit.
The IGN begins a 30-second purge cycle and the RRUCM
drives the Modulating Gas Actuator (MGA) to a low fire
start position and holds that position for 60 seconds.
Following the 30-second purge the IGN opens the gas
valve (GV) and begins a 15-second “single-try” ignition.
The IGN “single-try” energizes the Gas Ignitor (TNS5)
through PV Relay R7, MV Relay R8 and Gas Ignitor Power
Transformer (TNS6). At the end of the 15-second “single-
try” ignition, the IGN ends the ignition trial by energizing
R8.
The RRUCM monitors SAT at the STS and varies the 2–
10 Vdc output signal from the RRUCM Analog
Output (AO1) to the MGA modulating gas flow to the
burner to maintain HSP.
Burner operation will LOCK-OUT if either the ignition trial
fails to prove flame signal at the burner flame sensing rod
within the 15-second ignition trial or following successful
ignition any time a failure to maintain flame signal occurs.
To retry ignition after ignition failure, power must be
turned off for 30 seconds and then powered up. The
ignition process and timing sequences begin upon re-
establishment of power. Loss of flame signal following
successful ignition will permit a SINGLE RETRY following
a IGN 30-second purge time delay.
Y1 - O/AIR COOLING ENABLE SET POINT (CSP): 68°F–80°F
78°F DEFAULT
RCC PRE-SET SUCTION PRESSURE SETTING:
38°F SATURATED SUCTION TEMPERATURE (APX.)
114 LB
DEHUMIDIFICATION SET POINTS (OES1 & OES2): 23–30 BTU
(OES1)
28 BTU (OES1) & 34 BTU (OES2) DEFAULT
32–40 BTU
(OES2)
HGRH HEATING DEAD BAND (HGRHD):
±4–20°F
±5°F DEFAULT
HGRH SUPPLY AIR TEMPERATURE SETPOINT:
68°F DEFAULT
O/AIR HEATING ENABLE SET POINT (HESP):
50°F–80°F
60°F DEFAULT
OCCUPIED S/AIR HEATING SET POINT (HSP):
40°F–90°F
MINIMUM
HEATING SET
POINT
45°F DEFAULT
S/AIR LOW CUTOFF TEMPERATURE (SLT):
25°F–40°F
34°F DEFAULT
S/AIR LOW CUTOFF TIME (SLC):
15–30 MIN
15 MIN DEFAULT
S/AIR HIGH CUTOFF TEMPERATURE (SHT):
70°F–125°F
125°F DEFAULT
S/AIR HIGH CUTOFF TIME (SHC):
5–30 MIN
15 MIN DEFAULT
