Manual 2100-420H
Page 26 of 34
SEQUENCE OF OPERATION
Cooling – Circuit R-Y makes the thermostat pull in the
compressor contactor starting the compressor and
outdoor motor. The G (indoor motor) circuit is
automatically completed on any call for cooling
operation, or can be energized by manual fan switch on
subbase for constant air circulation.
Heating – A 24V solenoid coil on the reversing valve
controls heating cycle operation. Two thermostat
options, one allowing “Auto” change over from cycle to
cycle and the other constantly energizing solenoid coil
during heating season and thus eliminating pressure
equalization noise except during defrost, are to be used
on “Auto” option, a circuit is completed for R-W1 and
R-Y on each heating “on” cycle, energizing reversing
valve solenoid and pulling in compressor contactor
starting compressor and outdoor motor. R-G also makes
starting indoor blower motor. Heat pump heating cycle
now in operation.
The second option has no “Auto” change over position,
but instead energizes the reversing valve solenoid
constantly whenever the system switch on subbase is
placed in “Heat” position, the “B” terminal being
constantly energized from R. A thermostat demand for
heat completes R-Y circuit, pulling in compressor
contactor starting compressor and outdoor motor. R-G
also make starting indoor blower motor.
High / Low Pressure control provides protection for the
compressor. In the event system pressures go above 450
PSI or below 3.5 PSI in either cooling or heating mode,
the compressor will be stopped. This will activate the
red light located in the control panel. The lockout
circuit will hold compressor off line. When the system
problem is corrected, the unit operation can be restored
by turning of the main power supply off and then back
on, or reset the room thermostat. The low pressure
control has a bypass to eliminate nuisance lockout on
cold start up.
The bypass timer should be set to 200 seconds and this
is to assure there is no nuisance tripping of the low-
pressure control during startup in heating mode under
cold weather conditions. See Figure 22.
OPTIONAL CLIMATE CONTROLSSEQUENCE OF OPERATION
The Climate Control Option A is an electronic, non-
programmable manual or auto changeover thermostat.
The thermostat may be manually set to heat or cool
mode. The thermostat will maintain the temperature set
on the thermostat in the mode in which it is set.
The Climate Control Option D is an electronic,
programmable thermostat. The thermostat can be set in
the heat, cool or automatic mode. When the thermostat
is set in the heat mode, it can heat only to maintain the
temperature set on the thermostat. When the thermostat
is set in the cool mode, it can cool only to maintain the
temperature set on the thermostat. When the thermostat
is set in the automatic mode, the thermostat can change
automatically to the heat or cool modes to maintain the
temperature set on the thermostat.
PRESSURE SERVICE PORTS
High and low pressure service ports are installed on all
units so that the system operating pressures can be
observed. Pressure curves can be found later in the
manual covering all models on both cooling and heating
cycles. It is imperative to match the correct pressure
curve to the unit by model number. Upper and lower
service doors must be attached to obtain proper reading.
FIGURE 21
HEAT PUMP CONTROL BOARD (HPC)