Installation manual

54
Roth RCT Models, 16 Feb 2012D
SEQUENCE OF OPERATION:
Combination Units
Heating, 1st Stage (Y1,G) Forced Air
The ECM fan is started immediately at 75% (of 1st
stage operation) CFM level, fi rst stage compressor
and the loop/desuperheater pump(s) are energized
10 seconds after the “Y1” input is received. The ECM
fan adjusts to 100% (of 1st stage operation) CFM
level 30 seconds after the “Y1” input.
Heating, 2nd Stage (Y1,Y2,G) Forced Air
The ECM fan adjusts to 2nd stage CFM level, and
the compressor full load solenoid valve is energized
30 seconds after the “Y2” input is received.
Heat, 3rd Stage (Y1,Y2,W,G) Forced Air
The ECM fan remains at 100% of 2nd stage CFM
level, and the electric backup heat is energized.
Emergency Heat (W,G) Forced Air
The fan is started immediately at 100% of 2nd stage
CFM level, and the electric backup heat is energized.
Cooling Operation
The reversing valve is energized for cooling
operation. Terminal “O” from the thermostat is
connected to the reversing valve solenoid.
Cooling, 1st stage (Y1,0,G) Forced Air
The ECM fan is started immediately at 75% (of 1st
stage operation) CFM level, fi rst stage compressor
and the loop/desuperheater pump(s) are energized
10 seconds after the “Y1” input is received. The ECM
fan adjusts to 100% (of 1st stage operation) CFM
level 30 seconds after the “Y1” input.
Cooling, 2nd Stage (Y1,Y2,O,G) Forced Air
The ECM fan adjusts to 2nd stage CFM level, and
the compressor full load solenoid valve is energized
30 seconds after the “Y2” input is received.
Cooling, Dehumidifi cation Mode
The ECM control module includes two types of
dehumidifi cation modes, Forced Dehumidifi cation
mode, and On Demand Dehumidifi cation
(ODD). If the ECM control module is set to Forced
Dehumidifi cation mode, the ECM fan runs at
normal CFM in all heating stages, but all cooling
operation will be 85% of the current stage CFM
level, which lowers the CFM through the evaporator
coil, improving latent capacity. In ODD mode, a
humidistat or a thermostat with a dehumidifi cation
output (output must be reverse logic -- i.e. it must
operate like a humidistat) is connected to the
ODD terminal. When the module receives a call
for dehumidifi cation, the fan runs at 85% of the
current stage CFM in the cooling mode. Otherwise,
the airfl ow is at the normal CFM level. The signal is
ignored in the heating mode.
Fan Only
When the ECM control module receives a “G”
call without a call for heating or cooling, the fan
operates at 50% of the full load CFM level.
Hot Water Operation (HW)
First stage compressor, direction valve, 3-way valve,
load pump relay, and loop/desuperheater pump(s)
are energized 10 seconds after the Aqua-stat
(“HW”) input is received. The compressor full load
solenoid valve is energized 30 seconds after the
“HW” input is received. The compressor always runs
in full load (2nd stage) in hot water mode. NOTE:
Combination units can heat water, but do not have
chilled water capability.
Time Delays When Switching Modes
In order for the direction valve and 3-way valve
to switch properly, the system must have time for
the refrigerant pressures to equalize. The combo
board always initiates a two-minute delay when
switching from forced air mode to the hot water
mode to insure that the valves are not switched
before the pressures have equalized. The lockout
board initiates a fi ve-minute anti-short cycle delay
anytime the compressor signal is interrupted. For
example, if the unit is running in forced air heating,
and gets a call from the aqua-stat (when the board
is in hot water priority mode), the combo board will
de-energize the compressor. After two minutes,
the combo board will re-energize the compressor
relay, direction valve, and 3-way valve for hot water
mode operation. Even though the combo board is
calling for compressor, the lockout board still requires
an additional 3 minutes before the compressor has
been off for 5 minutes. Therefore, there will always
be fi ve minutes off time when switching mode
Section 14b: Combination Unit Controls