System Operations - Lennox Collection XC21 System Installation Instructions Manual

INSTALLING ISOLATION GROMMETS
Locate the isolation grommets (provided). Slide grommets
onto vapor and liquid lines. Insert grommets into piping
panel to isolate refrigerant lines from sheet metal edges.
SUCTION LINE
LIQUID LINE
TWO ISOLATION GROMMETS ARE
PROVIDE FOR THE LIQUID AND
SUCTION LINE PIPE PANEL PASS
THROUGH.
REAR VIEW OF UNIT EXTERIOR
Figure 24. Isolation Grommets
System Operation
IMPORTANT
Some scroll compressor have internal vacuum protector
that will unload scrolls when suction pressure goes
below 20 psig. A hissing sound will be heard when the
compressor is running unloaded. Protector will reset
when low pressure in system is raised above 40 psig. DO
NOT REPLACE COMPRESSOR.
The air conditioner control (A175) provides the following
system functions:
S
Compressor anti−short−cycle delay.
S
High (S4) and low (S87) pressure switches
S
Ambient (RT13) and Discharge Line (RT28)
Temperature Sensors Monitoring and Protection.
S
Five strikes lockout safety feature for High/Low
Pressure Switches
Temperature. See figures 27, 28 and 29 feature
function.
COMPRESSOR PROTECTION
CYCLE DELAY
The air conditioner control protects the compressor from:
S
Short cycling (five minutes) when there is initial power
up
S
Interruption in power to the unit
S
High or low pressure switch or discharge line sensor
trips
S
Delay after Y1 demand is removed.
506587−01
PIPING PANEL
and High Discharge Line
ANTI−SHORT
In non−communicating systems the delay is set for 300
seconds (five minutes) and can not be changed. To
override timer when active or inactive, place a jumper on
the field test pins between 1 and 2 seconds.
In communicating system, the icomfort Touch
has a separate built−in 5−minute non−adjustable short cycle
protection.
Resetting Anti−Short Cycle Delay
The E33 pins on the air conditioner control can be
jumpered between 1 to 2 seconds to reset the anti−short
cycle delay sequence.
HIGH (S4) AND LOW (S87) PRESSURE SWITCHES
Low Pressure Switch (LO−PS)
pressure switch sequence of operation.
High Pressure Switch (HI−PS)
pressure switch sequence of operation.
Pressure Switch Event Settings
The following pressures are the auto reset event value
triggers for low and high pressure thresholds:
S
High Pressure (auto reset) − trip at 590 psig; reset at
418.
S
Low Pressure (auto reset) − trip at 25 psig; reset at 40.
COMPRESSOR PROTECTION
LOCKOUT SAFETY FUNCTION
The five−strike lockout safety function is designed to
protect the unit's compressor from damage. The five−strike
feature is used for high pressure (S4) and low (S87)
pressure switch trips and high discharge temperature
(RT28).
Resetting Five−Strike Lockout
Once the condition has been rectified, power to the heat
pump control's R terminal must be cycled OFF, or a jumper
placed on the FIELD TEST pins between 1− to 2−seconds
to reset the heat pump control.
UNIT SENSORS
Sensors connect to the heat pump control through a
field-replaceable harness assembly that plugs into the
control. Through the sensors, the control detects outdoor
ambient, coil, and discharge temperature fault conditions.
As the detected temperature changes, the resistance
across the sensor changes. Tables 7 and 8 shows how the
resistance varies as the temperature changes for both
type of sensors. Sensor resistance values can be checked
by ohming across pins listed in table 6.
NOTE When checking the ohms across a sensor, be
aware that a sensor showing a resistance value that is not
within the range shown in table 6, may be performing as
designed. However, if a shorted or open circuit is detected,
then the sensor may be faulty and the sensor harness will
need to be replaced.
Page 30
® thermostat
See figure 27 for low
See figure 28 for high
FIVE−STRIKE