Sequences Of Operation; Power-Up; Fan Operation - Daikin RoofPak RPS Series Installation And Maintenance Manual

The following sequences of operation are for a typical "C"
vintage applied rooftop unit equipped with MicroTech III, an
economizer, 4-compressor/4-stage cooling, 3 to 1 turn down
burner, variable frequency drives (VFD), a return air fan and
an external time clock. These sequences describe the ladder
wiring diagram logic in detail; refer to
63 as you read them. Note that your unit's sequences of
operation may vary from those described here. Refer to the
wiring diagrams supplied with the unit for exact information.
For detailed description of operation information relating to
the MicroTech III controller's software, refer to the appropriate
operation manual (see Table 1 on page
describe the various setpoints, parameters, operating states,
and control algorithms that affect rooftop unit operation.

Power-up

When primary power is connected to the unit, 115 V (ac) power
is fed through control circuit transformer T1 and control circuit
fuse F1C (line 166, Figure 84 on page
crankcase heaters HTR-1, HTR-2, HTR-3 and HTR-4 (lines
502-540, Figure 90 on page
When system switch S1 (line 203,
is closed, low voltage transformers T2 (line 203,
page 76), T3 (line 251, Figure 88 on page
802, not shown) energize, and 115 V (ac) power is supplied to
the following:
• The supply fan VFD (line 135-137,
66)
• M40A to energize the return fan VFD (line 147-149,
Figure 84 on page 66)
• Heating control panel (line 603,
• Economizer actuator (lines 256-257)
Transformer T2 supplies 24 V (AC) power to terminals 24V
and COM on the main control board MCB (lines 207 and 208).
Transformer T2 supplies 24 V (AC) power to the following (see
Figure 84 on page 66):
• Switch S7 On-Auto-OFF (line 217)
• Enthalpy sensor OAE (line 247)
• External time clock contacts (line 215)
• Airflow interlock switch PC7 (line 228)
• Dirty filter switches PC5 and PC6 (lines 242 and 247,
not shown)
• Gas furnace alarm relay R24 (line 225, not shown)
• Freezestat switch FS1 (line 244, hot water or steam heat
only, not shown)
• Smoke detectors SD1 and SD2 (line 237)
The time clock, S7 switch , and emergency shutdown terminals
(lines 217-222) control fan operation.
NOTE: Unit ships with factory installed jumpers between TB2
101 and 105 and between 101 and 106.
www.DaikinApplied.com
Wiring Diagrams on page
3). These manuals
66) to compressor
76).
Figure 88 on page 72)
Figure 90 on
72) and T9 (line
Figure 84 on page
Figure 89 on page

Fan Operation

When the main control board (MCB) commands the supply and
return fans to start, the unit enters the Startup operating state.
As a result, a 3-minute timer is set, output MCB-BO3 (line 307)
energizes, and relay R26 energizes (line 306, not shown).
After the 3-minute timer expires, the unit enters the Recirc
operating state. As a result, output MCB-BO1 energizes relay
R67 (line 401). This gives a start signal to supply fan drive
AFD10 (line 445). Four seconds after MCB-BO1 is energized,
output MCB-BO2 energizes relay R68 (line 404). This gives a
start signal to return fan drive AFD20 (line 445).
Within 120 seconds after the fans start, the controller expects
airflow switch PC7 (line 228) to close and thus energize binary
input MCB-BI6. (If MCB-BI6 does not energize, the controller
assumes the fans did not start. It then shuts down the unit and
generates an alarm.)
During the Recirc operating state, the outside air damper is
held closed. The controller does this by energizing output
MCB-BO5 (line 318). On VAV units, output MCB-BO12, the
VAV box output, is also de-energized (line 309) during the
Recirc state.
The supply fan adjustable frequency drive (AFD10) is
modulated to maintain the duct static pressure setpoint. When
energized, output MCB-BO14 (line 407) drives AFD10 toward
increased capacity; MCB-BO13 (line 405) drives it toward
decreased capacity. On VAV units or CAV units equipped with
return fan capacity control, the adjustable frequency drive
(AFD20) is modulated to maintain an acceptable building static
pressure (using either VaneTrol logic or direct measurement
of building pressure; see the appropriate OM for more
information). When energized, output MCB-BO16 (line 409)
74)
drives AFD20 toward increased capacity; MCB-BO15 (line 411)
drives them toward decreased capacity.
NOTE: If the inverter bypass switch S4 (lines426 and 430)
is in the bypass position, MMP30 and MMP40 (line
132 and 144) protect the fans from excessive current
draw. If either the supply or return fan is drawing
excessive current, one of the MMPs triggers an
auxiliary contacts (line 426) and open the circuit,
causing both fans to stop.
57

Sequences of Operation

IM 926-3 • ROOFPAK APPLIED SYSTEMS
Sequences of Operation