41
IOM, BS/BT Models
Enertech Global
Section 9: Controls
fault retry mode. At startup, the low pressure switch
monitoring is suspended for 30 seconds to avoid
nuisance faults (If the low pressure switch is open
before startup then the unit will not start upon
receiving an Y1 call and will lock out instead).
High Pressure (HP)
If the high pressure switch opens, the compressor
operation will be interrupted, and the control will go
into fault retry mode. There is no delay between the
time the switch opens and the board entering into
fault retry mode. There is also no delay of switch
monitoring at startup. (If the high pressure switch is
open before startup then the unit will not start upon
receiving an Y1 call and will lock out instead.)
Flow Switch (FS)
If equipped, a flow switch ensures the source
water maintains the minimum required flow rate.
This ensures that pumps are working and water
connections remain intact. The flow switch will
also trip when the source water begins to freeze,
providing additional protection.
Hot Discharge Gas Temperature (DGT)
When the hot discharge gas temperature is above
220°F for 30 continuous seconds, the compressor
operation will be interrupted. The control will go into
fault retry mode.
Desuperheater Leaving Water Temp (DLWT)
Controls monitor the desuperheater leaving water
temperature (DLWT. The hot water generator pump
is de-energized when the leaving water temperature
(DLWT) is above 130°F or when the compressor
discharge line (DGT) is cooler than leaving water
temperature (DLWT).
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. When diagnosing a possible bad
sensor, the following table may be used to verify a
valid temperature reading
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
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.
When an O/U Voltage condition occurs, the board
will initiate a fault, shut down the compressor, and
start the five minute ASC period. All four fault LEDs
will flash (HP + LP + FS + CO) 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.
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 5 min. 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.