Manual 2100-718A
Page
16 of 26
120*
SW
1
SW
2
TIME (SEC)
OFF
OFF
ON
ON
OFF
ON
OFF
ON
30
60
180
MIS-2668 A
OFF
LOW PRESSURE BYPASS TIMER SWITCH
*(FACTORY SETTING 120 SECONDS)
ACCUMULATED DEFROST TIME TIMER
(FACTORY SETTING 60 MIN.)
ON
MIS-2668A
FIGURE 8
Defrost Control Board
run through the 1-minute minimum defrost length
sequence in a matter of seconds and will automatically
terminate the defrost sequence.
There is an initiate defrost jumper (sen jump) on the
control that can be used at any outdoor ambient during
the heating cycle to simulate a 0° coil temperature.
This can be used to check defrost operation of the unit
without waiting for the outdoor ambient to fall into the
defrost region.
By placing a jumper across the
SEN JMP
terminals (a
¼" QC terminal works best) the defrost sensor mounted
on the outdoor coil is shunted out and will activate the
timing circuit. This permits the defrost cycle to be
checked out in warmer weather conditions without the
outdoor temperature having to fall into the defrost region.
In order to terminate the defrost test, the
SEN JMP
jumper must be removed. If left in place too long, the
compressor could stop due to the high pressure control
opening because of high pressure condition created
by operating in the cooling mode with outdoor fan off.
Pressure will rise fairly fast as there is likely no actual
frost on the outdoor coil in this artificial test condition.
There is also a 5-minute compressor time delay
function built into the HPC. This is to protect the
compressor from short cycling conditions. The board’s
LED will have a fast blink rate when in the compressor
time delay. In some instances, it is helpful to the
service technician to override or speed up this timing
period, and shorting out the
SPEEDUP
terminals for a
few seconds can do this.
Low Pressure Switch Bypass Operation
The control has a selectable (SW1) low pressure switch
bypass set up to ignore the low pressure switch input
during the first (30, 60, 120 or 180 seconds) of “Y”
operation. The default setting is 120 seconds.
After this period expires, the control will then monitor
the low pressure switch input normally to make sure
that the switch is closed during “Y” operation.
High Pressure Switch Operation
The control has a built-in lockout system that allows
the unit to have the high pressure switch trip up to two
times in one hour and only encounter a “soft” lockout.
A “soft” lockout shuts the compressor off and waits
for the pressure switch to reset, which at that point
then allows the compressor to be restarted as long
as the 5-minute short cycle timer has run out. If the
high pressure switch trips a third time within one hour,
the unit is in “hard” lockout indicating something is
certainly wrong and it will not restart itself.
Alarm Terminal
– If hard lockout is entered, "L" terminal
on defrost control board will become active with 24V,
activating alarm relay, if present (optional). Cycling
thermostat or main power will relieve lockout condition.
