System Operations - Lennox XC21 Series Unit Information

°F
−40
−35
−30
−25
−20
−15
−10
−5
0
5
10
15
20
25
30
35
40
45
50
55
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 main 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 33, 32 and 34 feature
function.
COMPRESSOR ANTI−SHORT CYCLE DELAY
The main 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.
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.
XC21
Table 5. HFC−410A Temperature (°F) − Pressure (Psig)
°C Psig
−40.0 11.6
−37.2 14.9
−34.4 18.5
−31.7 22.5
−28.9 26.9
−26.1 31.7
−23.3 36.8
−20.6 42.5
−17.8 48.6
−15.0 55.2
−12.2 62.3
−9.4 70.0
−6.7 78.3
−3.9 87.3
−1.1 96.8
1.7 107
4.4 118
7.2 130
10.0 142
12.8 155
and High Discharge
°F
60
65
70
75
80
85
90
95
100
105
110
115
120
125
130
135
140
145
150
In communicating system, the icomfort Toucht thermostat
has a separate built−in 5−minute non−adjustable short cycle
protection.
Resetting Anti−Short Cycle Delay
The E33 pins on the main control can be jumpered
between 1 to 2 seconds to reset the anti−short cycle delay
sequence.
HIGH (S4) AND LOW (S87) PRESSURE SWITCHES
The unit's reset pressure switches LO PS (S4) and HI PS
(S87) are factory−wired into the main control on the LO−PS
and HI−PS terminals, there locations are illustrated on page
5. Sequence of operations for both pressure switches are
provided in figures 33 and 32.
HIGH DISCHARGE LINE TEMPERATURE
(RT28)
The high discharge line temperature sensor location is
illustrated on page 5. This sensor's sequence of
operations is provided in figure 34.
Line
High Discharge Line Sensor Open/Shorted Event
Discharge sensor open / short fault is ignored during initial
90−seconds of compressor run time. After that, if discharge
temperature sensor is detected open or short, the control
will de−energize all the outputs and anti−short cycle timer is
started. Discharge sensor faulty alert LED code will be
displayed.
OUTDOOR AMBIENT TEMPERATURE (RT13)
If the outdoor ambient temperature sensor detected a
open, or out of range −40ºF to +140ºF (−40ºC to 60ºC) then
LED alert codes are displayed, however cooling operation
will continue. See table 9 for LED alert codes for the
ambient sensor. Location of outdoor ambient temperature
sensor is illustrated on page 5.
Page 32
°C Psig
15.6 170
18.3 185
21.1 201
23.9 217
26.7 235
29.4 254
32.2 274
35.0 295
37.8 317
40.6 340
43.3 365
46.1 391
48.9 418
51.7 446
54.4 476
57.2 507
60.0 539
62.8 573
65.6 608
SENSOR
Condition