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Brownout/Surge/Power Interruption Protection
The brownout protection in the UPM board will shut does the
compressor if the incoming power falls below 18 VAC. The com-
pressor will remain OFF until the voltage is above 18 VAC and
ANTI-SHORT CYCLE TIMER (300 seconds) times out. The unit
will not go into a hard lockout.
Malfunction Output
Alarm output is normally open (NO) dry contact. If pulse is select-
ed the alarm output will be pulsed. The fault output will depend on
the DIP switch setting for ALARM. If it is set to CONST, a con-
stant signal will be produced to indicate a fault has occurred and
the unit requires inspection to determine the type of fault. If it is
set to PULSE, a pulse signal is produced and a fault code is detect-
ed by a remote device indicating the fault. The remote device must
have a malfunction detection capability when the UPM board is
set to PULSE.
LED Fault Indicator
The UPM includes an alarm indicator with blink codes to indicate
a UPM fault. (See Table 32.)
Table 32 — UPM Board Fault Blink Codes
LED
FAULT
BLINKS
0
None
1
High Pressure
2
Low Pressure
Water Coil Freeze
3
Condition
Condensate Overflow Condensate levels in the unit drain pan
4
5
Brown Out
Air Coil Freeze
6
Condition
Freeze Protection Sensors 1 and 2 (FP1 and FP2)
FP1 is located on the refrigerant liquid line between the TXV and
the coaxial heat exchanger. If the temperature of the refrigerant en-
tering the coaxial coil (heating mode) drops below or remains at
26°F (–6.6°C) for 30 seconds the UPM controller will shut down
the compressor and enter into a soft lockout condition. Both the
status LED and the Alarm contact will be active. The LED will
flash three (3) times for this alarm condition. If this alarm occurs 2
times (or 4 times if the Lockout DIP switch is set to 4) within an
hour the controller will enter into a hard lockout condition. The
FP1 freeze limit trip can be lowered to 15°F (–9.4°C) by cutting
the R30 sensor located near the top of DIP switch SW1. However,
careful consideration should be given before cutting resistor R30.
For example, if the unit is employing a fresh water system resistor
R30 should remain to protect the coaxial heat exchanger from
freezing and damaging the unit.
FP2 is located on the refrigerant liquid line between the TXV and
the indoor coil. If the temperature of the refrigerant entering the in-
door coil (cooling mode) drops below or remains at 26°F (–6.6°C)
for 30 seconds the UPM controller will shut down the compressor
and enter into a soft lockout condition. Both the status LED and
the Alarm contact will be active. The LED will flash six (6) times
for this alarm condition. If this alarm occurs 2 times (or 4 times if
the Lockout DIP switch is set to 4) within an hour the controller
will enter into a hard lockout condition. The FP2 freeze limit trip
can be lowered to 15°F (–9.4°C) by cutting the R24 sensor located
near the top of DIP switch SW1. However, careful consideration
should be given before cutting resistor R24. For example, a low
refrigerant temperature could cause frosting on the indoor coil,
which restricts airflow causing the unit to malfunction.
Intelligent Reset
If a fault condition is initiated, the 5 minute delay on break time
period is initiated and the unit will restart after these delays expire.
FAULT CRITERIA
All fault conditions nominal
Refrigerant discharge pressure has
exceeded 600 psig
Refrigerant suction pressure has fallen
below 40 psig
Refrigerant temperature to the water coil
has fallen below 26°F for 30 seconds
are too high
Control voltage has fallen below 18 VAC
Refrigerant temperature to the air coil
has fallen below 26°F for 30 seconds
During this period the fault LED will indicate the cause of the
fault. If the fault condition still exists or occurs 2 or 4 times (de-
pending on 2 or 4 setting for LOCKOUT DIP switch) before 60
minutes, the unit will go into a hard lockout and requires a manual
lockout reset. A single condensate overflow fault will cause the
unit to go into a hard lockout immediately, and will require a man-
ual lockout reset.
Lockout Reset
A hard lockout can be reset by turning the unit thermostat off and
then back on when the RESET DIP switch is set to "Y" or by shut-
ting off unit power at the circuit breaker when the RESET DIP
switch is set to "R".
Selectable Alarm Mode
The UPM board can be configured to have either a constant or
pulse signal. If constant (CONT) is selected the UPM will provide
a closed contact at the alarm output until the alarm is cleared. If
pulsed (PULSE) is selected the UPM will sequence the alarm con-
tact with the fault LED flashes.
Test Mode (TEST)
In test mode the ASC and Random Start time delays are reduced
(5 seconds and 10 seconds respectively), and serve no function to
the end user equipment. The alarm and display relays also pulse
for both soft and hard lockout conditions, and are both cleared
through a manual reset.
UPM Sequence of Operations
Figure 39 shows the UPM sequence of operations.
Freeze Protection Sensors
The control system employs 2 nominal 10,000 ohm thermistors
(FP1 and FP2) that are used for freeze protection. Be sure FP1 is
located on the refrigerant line between the TXV and the condenser
coil and FP2 is located on the refrigerant line between the TXV
and the evaporator coil. See Fig. 46.
Thermostatic Expansion Valves
Thermostatic expansion valves (TXV) are used as a means of me-
tering the refrigerant through the evaporator to achieve a preset su-
perheat at the TXV sensing bulb. Correct superheat of the refriger-
ant 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 re-
frigerant in both modes of operation. When diagnosing possible
TXV problems it may be helpful to reverse the refrigerant 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 operating pressures.
Therefore, diagnosing TXV problems can be difficult.
TXV FAILURE
The most common failure mode of a 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 dia-
phragm will vary, depending on the pressure inside of the sens-
ing bulb. As the temperature of and pressure within the bulb de-
creases, the valve will modulate closed and restrict the refriger-
ant 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 diaphragm 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 there is inadequate flow
for the heat pump to operate.
59
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