Table of Contents
Advertisement
90.0
E
$
CC
80.0
70.0
60.0
,50.0
40.0
30.0
20.0
10.0
0.0
0.0
\
\
\
20.0
40.0
60.0
80.0
100.0
120.0
140.0
Temperature
(degF)
Fig. 40 -- Thermistor Nominal Resistance
WSHP
Open
Controller
-- With the WSHP Open con-
troller option, the 100 most recent alarms can be viewed using
the BACview 6 alarm status and alarm history.
To view the alarms:
1. Navigate
to the Alarm
Status
screen
from the Home
screen using the arrow softkeys. The screen will display
the current alarm status, either normal or Alarm, and al-
low for scrolling through the unit's alarm status.
2. From the Alarm Status screen, press the Alarm softkey to
view the 100 most recent alarms which are labeled with
date and time for easy reference.
NOTE:
Active faults can be viewed
by scrolling down,
these faults indicate a possible bad sensor or some condi-
tion which may not merit an alarm.
3. To view alarms which have been corrected, scroll down
through the Alarm screen to Return Top Normal screen.
NOTE:
Alarms
are automatically
reset once alarm con-
dition has been corrected.
See Table 32 for possible alarm cause and solution.
Thermostatic
Expansion
Valves--Thermostat-
ic expansion valves (TXV) are used as a means of metering the
refrigerant through the evaporator to achieve a preset superheat
at the TXV sensing bulb. Correct superheat of the refrigerant is
important for the most efficient operation of the unit and for the
life of the compressor.
Packaged
heat pumps
typically
use one bi-flow
TXV to
meter refrigerant in both modes of operation.
When diagnosing
possible TXV problems it may be helpful to reverse the refrig-
erant flow to assist with the diagnosis.
Geothermal
and water source heat pumps
are designed to
operate through
a wide range of entering-water
temperatures
that will have
a direct
effect on the unit refrigerant
oper-
ating pressures.
Therefore,
diagnosing
TXV problems
can be
difficult.
TXV FAILURE -- The most COlnmonfailure mode ofa TXV
is when the valve fails while closed. Typically, a TXV uses
spring pressure to close the valve and an opposing pressure,
usually from a diaphragm, to open the valve. The amount of
pressure exerted by the diaphragm will vary, depending on the
pressure inside of the sensing bulb. As the temperature of and
pressure within the bulb decreases, the valve will modulate
closed and restrict the refrigerant flow through the valve. The
result is less refrigerant in the evaporator and an increase in the
superheat. As the temperature at the bulb increases the dia-
phragm pressure will increase, which opens the valve and
allows more refrigerant flow and a reduction in the superheat.
If the sensing bulb, connecting capillary, or diaphragm
assembly are damaged, pressure is lost and the spring will force
the valve to a closed position. Often, the TXV will not close
completely so some refrigerant flow will remain, even if inade-
quate flow for the heat pump to operate.
The TXV sensing bulb must be properly located, secured,
and insulated as it will attempt to control the temperature of the
line to which it is connected. The sensing bulb must be located
on a dedicated suction line close to the compressor. On a pack-
aged heat pump, the bulb may be located ahnost any place on
the tube running from the compressor suction inlet to the
reversing valve. If the bulb is located on a horizontal section, it
should be placed in the 10:00 or 2:00 position for optimal
performance.
Use caution when tightening
the strap. The strap must be
tight enough to hold the bulb securely but caution must be
taken not to over-tighten
the strap, which could dent, bend,
collapse or otherwise
damage the bulb.
AIRFLOW
(°F)
THERMISTOR
,_ AR_
_COIL\\
AIRFLOW
EXPANSION
\vf_) .....
VALVE
OVERFLOW
(CO)
AIR COIL
FREEZE
WATER
PROTECTION
COIL
FP1
T
1
WATER
IN
WATER OUT
PROTECTION
LEGEND
COAX
--
Coaxial Heat Exchanger
•_
Airflow
Refrigerant
Liquid Line Flow
Fig. 41 -- FP1 and FP2 Thermistor Location
f
SUCTION
COMPRESSOR
DISCHARGE
J
47
Advertisement
Table of Contents
