Lennox Merit Series 13HPX Units Installation Instructions Manual page 14

CHECKING
The 13HPX unit is factory-charged with enough HFC-410A
refrigerant to accommodate a 15-foot length of refrigerant
piping. Charge should be checked and adjusted using the
tables provided on the charging procedure sticker on the unit
access panel. Detailed information is given in the 13HPX
Installation and Service Procedures manual, which is
available on DaveNet.
Defrost System
The defrost system includes a defrost thermostat (S6) and a
defrost control (CMC1).
DEFROST CONTROL (CMC1)
This defrost control includes the combined functions of a
time/temperature defrost control, defrost relay, time delay,
diagnostic LEDs, and a terminal strip for field wiring
connections.
The defrost control provides automatic switching from
normal heating operation to defrost mode and back. When
the defrost thermostat is closed, the control accumulates
compressor run time at 30, 60 or 90 minute field adjustable
intervals. When the selected compressor run time interval is
reached, the defrost relay is energized and defrost begins.
Defrost Control Timing Pins (P1)
Each timing pin selection
accumulated compressor run time period for one defrost
cycle. This time period must occur before a defrost cycle is
initiated. The defrost interval can be adjusted to 30 (T1),
60 (T2), or 90 (T3) minutes (see figure 17). The maximum
defrost period is 14 minutes and cannot be adjusted.
NOTE — Defrost control part number is listed near the P1
timing pins.
•
Factory default is 90 minutes.
•
If the timing selector jumper is missing, the defrost
control defaults to a 90-minute defrost interval.
Compressor Delay (P5)
The defrost control has a field-selectable function to reduce
occasional sounds that may occur while the unit is cycling in
and out of the defrost mode.
The compressor will be cycled off for 30 seconds going in
and out of the defrost mode when the compressor delay
jumper is installed.
NOTE — The 30‐second compressor feature is ignored
when the TEST pins have been jumper.
provides a different
Page 14
Time Delay
The timed‐off delay is five minutes long. The delay helps to
protect the compressor from short‐cycling in case the power
to the unit is interrupted or a pressure switch opens. The
delay is bypassed by placing the timer select jumper across
the TEST pins for 0.5 seconds.
The TEST mode is activated by removing the jumper on the
defrost termination pins (30, 60 or 90) and placing the
jumper on the TEST pins after 24VAC is applied to the
control. The low pressure input is ignored in TEST mode.
IMPORTANT
The TEST pins are ignored and the TEST function is
locked out:
S
If the jumper is applied on the TEST pin before 24VAC
is applied to the control.
S
If there is a jumper on the 30 or 60 minute defrost ter­
mination pins.
Bypass-Anti-Short Cycle Delay
The Y1 input must be active ON, the high pressure switch
must be closed or a jumper must be installed on the high
pressure terminals of the control.
Initiate a Force Defrost
The Y1 input must be active ON, the high pressure switch
must be closed or a jumper must be installed on the high
pressure terminals of the control, the defrost thermostat
must be closed or a jumper must be placed across the DF
terminals on the control and the O terminals must not have
24VAC (no power to reversing valve) before control will enter
into a force defrost.
Test Mode Sequence
Using the defrost termination pin, short the TEST pins for a
period of two seconds:
•
Clear timed lockout / or pressure switch lockout
function.
•
Enter defrost mode
After entering force defrost, if the jumper is removed before
5 seconds has elapsed, the unit will remain in forced defrost
mode until defrost thermostat opens or terminated on
maximum defrost time (14 minutes). If the jumper is not
removed, once 5 seconds has elapsed (7 seconds total), the
unit will terminate defrost and return to heat mode. The
TEST mode will then be locked­out and no further TEST
mode operation will be executed until the jumper on the
TEST pins is removed and re­applied to the applicable
defrost termination pins.
Test Mode