Sequence Of Operation; Crv / Qerv Operation; Optional Climate Controls Sequence Of Operation; Pressure Service Ports - Bard QTEC Q24A1D Series Installation Instructions Manual

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 – Circuit is completed for R-W1 on each
heating "on" cycle, energizing the electric heat
contactor. R-G also makes starting indoor blower
motor.
Second stage heat – Energized circuit R-W2 and the
electric heat contactor for the second bank of heaters (if
equipped) is energized.
High / Low Pressure control provides protection for the
compressor. In the event system pressures go above 600
PSI or below 40 PSI in cooling 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,
factory set to 2 minutes.
Dehumidification / Reheat Circuit – Both cooling and
heating take precedence over dehumidification.
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 24 and 25 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.

CRV / QERV OPERATION

QERV is energized by applying 24 VAC to the "F"
terminal of the low voltage terminal strip on units with
"X" climate control option. It is energized by the "A"
terminal of the thermostat on units with "E" climate
control option. It is energized by applying power to the
"F" terminal of the low voltage strip on units with "G"
climate control options. On climate option "I" it is
energized by the brown/white wire at the CO
Manual 2100-523
Page 34 of 41
OPTIONAL CLIMATE CONTROLS
SEQUENCE OF OPERATION
The Climate Control Option G 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 E 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.
The Climate Control Option I is an electronic,
programmable thermostat and a CO
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.
The CO
2
ID blower when the room CO
Default CO

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.
CO CONTROLLER – FACTORY SET TO 1000 PPM
2
controller.
2
"SW2" SET TO ON
controller will energize the vent option and the
levels rise over set level.
2
set point is 1000 ppm. See Figure 23.
2
FIGURE 23
SW2SW1OUT AN
"AN" SET TO VOLTAGE
"SW1" SET TO ON "OUT" SET TO 20-100%
controller. The
2
MIS-2667