Heating - Daikin RDT-135c Installation And Maintenance Manual

Sequences of Operation: Heating
setpoints input through the keypad. CCB2-BO6 controls
contactor M22 (line 866), which cycles condenser fan 22.
CCB2-BO7 controls contactor M23 (line 867), which cycles
condenser fan #23. This is stage 2.
If more cooling is required, CCB1-BO2 energizes contactor
M3 (line 822) to start compressor #3. This is stage 3.
If more cooling is required, CCB2-BO2 energizes contactor
M4 (line 855) to start compressor #4. This is stage 4.
When the cooling demand is satisfied, MCB works through
CCB1 and 2 to stage down the compressors. The compressor
with the most hours on the lag circuit stages off first, and so
on. When both circuits are running with only one compressor
each (stage 2) and less cooling is required and if circuit #2 is
lag, CCB2-BO4 de-energizes to close liquid line solenoid
valve SV2 (line 864). As a result, compressor #2 pumps down
refrigeration circuit #2 until the suction pressure drops low
enough to open low pressure control LP2 (line 848). When
LP2 opens, CCB2-BO1, BO5, (BO6 and BO7) de-energize to
shut down compressor #2 and its associated condenser fan(s).
When mechanical cooling is no longer necessary, CCB1-BO4
de-energizes to close liquid line solenoid valve SV1 (line 831).
As a result, compressor #1 pumps down refrigeration circuit
#1 until the suction pressure drops low enough to open low
pressure control LP1 (line 815). When LP1 opens,
CCB1-BO1, BO5, (BO6 and BO7) de-energize to shut down
compressor #1 and its associated condenser fan(s).
Lead Circuit Loading
The loading and unloading process is similar except that both
compressors in the lead cooling circuit energize before
energizing any compressors in lag circuit.
Compressor Protective Devices (see page 118)
If a compressor motor protector trips, it immediately disables
its associated compressor contactor M1, 2, 3 or 4 (lines 817,
850, 822 and 855).
If high pressure switch HP3 trips (line 823), compressors #1 and
#3 are disabled and relay R1 (836) signals CCB1-BI7 of the
event (line 807). CCB1 then de-energizes CCB1-BO1 and BO2
(lines 817, 822) to keep compressors #1 and #3 locked out. If
high pressure switch HP4 trips (line 856), compressors #2 and
#4 are disabled and relay R2 (line 869) signals CCB2-BI7 of the
event (line 840). CCB2 then de-energizes CCB2-BO1 and BO2
(lines 850 and 855) to keep compressors #2 and #4 locked out.
The following frost control protection option is not
Note:
included in the wiring diagram (Figure 84 on page 84).
If frost protect switch FP1 trips (line 811), CCB1-BO4
de-energizes (lines 831) to close SV1 and pump down circuit
#1. If frost protect switch FP2 trips (line 844), CCB2-BO4
de-energizes (lines 864) to close SV2 and pump down circuit
#2. For both of these alarms, the circuit remains off for at least
one cooling stage timer interval. If cooling is still needed, the
cooling tries to restart. The cooling resets up to three times in a
60
24-hour period (between 2:00 a.m. and 2:00 a.m.). After the
third trip, the alarm remains until manually cleared at the
keypad or over the network.

Heating

Gas Furnace, Modulating Burner (3 to 1 turn down)
Refer to "Standard Mod, furnace control (1000 MBH)" on
page 81 as you read this sequence of operation. Note that the
gas furnace wiring diagrams supplied with the units include a
detailed sequence of operation. Refer to the wiring diagram
supplied with the unit for exact wiring and sequence of
operation information.
When system switch S1 is closed, 115 VAC power is supplied
to the furnace control circuit and terminal 5 (line 609) on the
flame safeguard control (FSG) energizes as does the
modulating gas valve VM1. If heating is enabled (MCB-BI4 is
energized—line 223) and heating is required, the MCB-BO11
energizes relay R20 (line 413). The normally open R20
contacts (line 603) close, and if manual burner switch S3 and
safeties HL22, HL23, FLC (high limit switch) (line 603), LP5,
and HP5 are closed (optional, not shown on page 81), terminal
6 (line 618) on the flame safeguard control (FSG) energizes.
FSG energizes terminal 4 to start the blower motor (BM) (line
609) through contactor M29 on large burners. If the blower is
operational, air switch AS (line 621) closes and makes
electrical continuity from FSG terminal 6 to 7. After a 90-
second prepurge period, FSG terminals 8 (line 613) and 10
(line 621) energize. As a result, ignition transformer IT and
pilot gas valve GV1 energize. The pilot flame ignites and is
detected by FSG through flame rod FD (line 612). Upon
detection of pilot flame after the 10-second trial for ignition
period, the FSG de-energizes terminal 10 and energizes
terminal 9 to energize main gas valves GV2 and GV3 (lines
617, 619) and low fire start relay R23 (line 624). The R23
contacts (lines 632 and 633) allow the MCB to modulate gas
valve actuator VM1 as required to satisfy the heating demand.
Whenever the burner is operating, its firing rate is determined
by the position of gas valve actuator VM1. This actuator
modulates the butterfly gas valve and combustion air damper,
thus varying the furnace firing rate between 33% and 100% of
full capacity. When the MCB-BO10 energizes (line 634), VM1
modulates toward open and the firing rate increases. When
MCB-BO9 energizes (line 633), VM1 modulates toward
closed and the firing rate decreases. When both MCB-BO10
and MCB-BO9 are open, VM1 holds its position and the firing
rate remains constant.
When heating is no longer necessary, MCB-BO11 opens,
de-energizing relay R20 and opening its contacts (line 603). As
a result, the flame safeguard control de-energizes, all gas
valves close, the combustion air blower motor stops, and gas
valve actuator VM1 closes. If the furnace is warm enough to
close it, the FLC fan controls switch (line 602) overrides
supply fan start/stop output MCB-BO1 through R25 (line 402)
IM 738-2