22
Enertech Global
HP IOM, Rev. B
Load Heat Exchanger Freeze (T1)
When in cooling mode, if the heat exchanger temperature is
lower than 30°F for 10 continuous seconds, the compressor
operation will be interrupted, and the control will go into fault
retry mode. This sensor is located on the refrigerant line in
between the heat exchanger and TXV (refrigerant inlet of heat
exchanger in cooling mode).
Source Heat Exchanger Freeze (T4)
When in heating mode, if the heat exchanger is lower than
the setpoint for 10 continuous seconds, the compressor
operation will be interrupted, and the control will go into
fault retry mode. The setpoint is 12°F for closed loop (DIP
switch AFRZ = ON) and 30°F for open loop (DIP switch AFRZ
= OFF). At startup, the flow sensor is not monitored for 30
seconds to avoid nuisance faults. This sensor is located on the
refrigerant line in between the source heat exchanger and TXV
(refrigerant inlet of heat exchanger in heating mode).
Domestic Water Safety
Only Vented Units equipped to heat domestic hot water
require a separate electrical safety circuit. Units with domestic
water creation include an additional contactor which is
energized through a thermal switch. This switch is attached
to the load outlet and ensures water temperature does not
exceed 150°F. Should temperatures reach this point, the
switch will open and the secondary contactor will open,
disabling the compressor.
Thermistor Sensors
The following table indicates the normal operating range of
the temperature sensing thermistors. Readings outside this
range are indicative of a bad sensor. The Lockout Board will
display the associated fault.
Fault Retry
All faults (except O/U Voltage and Bad Thermistor Sensors) are
retried twice before finally locking the unit out (three faults
total).
The fault retry feature is designed to prevent nuisance service
calls. There is an anti-short cycle (ASC) period of 8 minutes
between fault retries. On the third fault of the same sensor,
within 30 minutes, the board will go into lockout mode and
the “Call For Service” indicator on the thermostat will flash
the number of pulses that correspond to the fault as shown in
Fault Indication Table.
Intelligent Lockout Reset
If the thermostat is powered off (Y1 removed) for one minute
then back on (soft reset), the board will reset and the last fault
will be stored in memory for ease of troubleshooting. If main
power is interrupted to the board, the fault memory will be
cleared (hard reset).
Control Board Switch Settings and Diagnostics
For fast and simple control board diagnosis, the lockout board
includes five LEDs: Green, Orange, Red, Yellow, and a Green
status indicator�
The Lockout Board LED Identification Table is located on
the following page.
Section 7: Controls
Temp.
(°F)
Resistance
(KΩ)
TEMP.
(°F)
Resistance
(KΩ)
10
46�95
130
3�60
15
41�39
200
1�16
20
36�50
220
0�87
30
28�61
250
0�59
77
10�00
257
0�54
When an O/U Voltage condition occurs, the board will initiate
a fault, shut down the compressor, and start the 8 minute ASC
period. All four fault LEDs will flash and the thermostat “Call
For Service” indicator will be flashing 11 pulses.
This feature is self- resetting and never retries or locks out. If
voltage returns to normal range, normal operation will resume
if/when the ASC period is over. When normal operation is
restored the four fault LED’s will stop flashing and the “Call For
Service” indicator will turn off.
When diagnosing a possible bad sensor, the following table
may be used to verify a valid temperature reading.
Temperature Sensor Operating Range
Sensor Name
Range
T1
10-200
T2
20-257
T3
20-220
T4
10-220
Over/Under Voltage Protection
The lockout board protects the compressor from operating
when an over/under voltage condition exists. The control
monitors secondary voltage from the transformer (24VAC) to
determine an over/under voltage condition is occurring on
the primary side of the transformer. Under voltage (<18VAC)
causes the compressor to disengage and restart when the
voltage returns to >20VAC. Over voltage (>31VAC) causes the
compressor to disengage and restart when the voltage returns
to <29VAC.
