Two-Speed Control Fault Conditions - Lennox HP21 Unit Information

Two-Speed Control Fault Conditions

If the control is in low speed operation, high speed opera-
tion, OFF" mode or speed change delay, the control
counts" or accumulates faults on an internal cycle counter.
Only faults which occur during compressor operation and
which cause the compressor to shut off are counted. After a
fault is counted, the control stops unit operation, resets and
begins a five minute time delay (step 2, operation se-
quence). If the control senses a fault at the end of five
minutes, the unit will not restart. If the control counts three
faults during the same thermostat demand, the control
locks out unit operation.
NOTE−If the control locks out, it can be reset by break-
ing thermostat demand for about five seconds then
remaking thermostat demand. Also, anytime thermo-
stat demand is removed or power is interrupted, the
control resets to zero faults.
A fault occurs when
1− Compressor operation is monitored by high pressure
switch and crankcase temperature thermostat. These
controls are wired in series. If either one trips, com-
pressor operation is interrupted and one fault is
counted. High pressure switch must be reset manually
but crankcase temperature switch resets automatical-
ly.
IMPORTANT-If the cycle counter counts three faults
during the same thermostat demand, the control locks
out. The outdoor unit remains inoperable until thermo-
stat demand is broken. This indicates further
troubleshooting is needed. Though the control can be
reset by breaking thermostat demand, the unit may re-
main inoperable. The
temperature conditions may still exist and must be lo-
cated and corrected before the unit can be placed back
in service.
high pressure or high
It is likely that the control could count three unit faults
from the crankcase temperature switch during a single
thermostat demand since this switch resets automati-
cally. However, the cycle counter can only count unit
faults from the high pressure switch if the reset button
is pushed without interrupting thermostat demand.
2− On all units using the TSC two-speed control, terminals
S1 and S2 on the control are connected to temperature
sensors (thermistors) which monitor the temperature
of the compressor motor windings. The two-speed
control measures the resistance through the sensors.
The sensors increase their resistance as temperature
increases (for example, too much superheat). When
the resistance through the sensors increases above a
preset limit, the control stops compressor operation.
As the compressor windings cool, the resistance
through the sensors drops below the reset limit, the
control resets automatically and one fault is counted.
NOTE-Intermittent continuity (bad connection or failing
components) can cause false lockout or lit LED. Check
all electrical connections thoroughly.
The sensors can be checked by measuring resistance
(ohms) through the sensors with the wires discon-
nected from the control (unit not running). The sensor
wires are not polarity sensitive. Table 3 shows winding
temperature sensor resistance values which will cause
the TSC to lock out. When the unit is operating normal-
ly, the resistance through the sensors should be below
the trip value shown in table 3.
The control can be checked by comparing the resist-
ance measured through the sensors to the voltage
measured across the sensor terminals with the unit
running. Table 4 shows voltage measured across two-
speed control terminals S1 and S2 with the
compressor running.
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