Bard QTEC QH303D, Installation Instructions Manual

Manual 2100-435D
Page

28 of 38

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 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.

Reheat Circuit 

– There is a small capillary tube inserted

between the reheat coil return line and suction line that
will prevent liquid from accumulating in the reheat coil
when it is inactive.  This drain does not affect the
normal operation of the system.

There is a check valve located in the reheat coil return
line.  It has a soft spring to hold the ball on the seat. This
will make the method of checking the ball freedom with
a magnet difficult.  Refer to Figures 18 and 19 for the
location of the check valve and drain back capillary.

When the system is operating in the dehumidification
mode the suction pressure will be reduced by 4 to 8 psig
and the discharge pressure will be reduced by 19 to 22
psig.

Return Air Thermostat 

– In dehumidification mode if

the return air temperature is lower than 65°, the return
air thermostat closes and brings on stage one electric
heat to maintain 65°.

High / Low Pressure Control

 provides protection for

the compressor.  In the event system pressures go above
350 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.  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 19.

OPTIONAL CLIMATE CONTROLS
SEQUENCE OF OPERATION

The Climate Control 

Option E

 is an electronic,

programmable thermostat and a humidistat.  This unit
has a refrigerant reheat circuit that is controlled by a 3
way valve.

When the humidity is above the setpoint of the
humidistat, the compressor circuit and the 3 way valve
are energized and the evaporator air flow is reduced.
The 3 way valve directs hot discharge gas into a
separate desuperheating condenser circuit that reheats
the conditioned air before it is delivered to the room.
When the humidistat is satisfied, the system switches
back to normal air conditioning mode.

If the thermostat calls for cooling during
dehumidification mode, the call for cooling takes
precedence over the dehumidification and the unit will
cool until the thermostat is satisfied.  Once the call for
cooling is satisfied, the unit may continue to
dehumidify.

If the thermostat calls for heat when the unit is in the
dehumidification mode, the electric heaters will
energize and the evaporator air flow will return to the
heating air flow.  When the thermostat is satisfied, the
electric heaters will turn off and the air flow will be
reduced and the system will continue to dehumidify
until humidistat is satisfied.

If the unit is running in heat pump mode and the
humidistat calls for dehumidification, the
dehumidification mode takes precedence over the heat
pump heating mode.  The unit will not return to the
heating mode until 2nd stage heating is called for.

The Climate Control 

Option F

 has a non-programmable

electronic thermostat, timer, and humidistat.  This unit
has a refrigerant reheat circuit that is controlled by a
3 way valve.

Unit operation is controlled by the manually operated
timer.  Normal heating, cooling or ventilation is
available only when the timer is on. Dehumidification
can be set to be available only when the timer is on, or
to be available continuously by switching a jumper on
the relay logic board.  See notes on Table 12.

Fan thermostat output should be programmed to be on
continuously when used with a vent option.

When the humidity is above the setpoint of the
humidistat, the compressor circuit and the 3 way valve
are energized and the evaporator air flow is reduced.
The 3 way valve directs hot discharge gas into a
separate desuperheating condenser circuit that reheats
the conditioned air before it is delivered to the room.  If