Loading ...
Loading ...
Loading ...
506318-03CPage 8 of 11 mrcool.com
During a single demand cycle, the defrost control will lock
by any pressure switch wired to the control board. In
addition, the diagnostic LEDs will indicate a locked-out
pressure switch. The unit will remain locked out until power
to the board is interrupted, then re-established or until the
jumper is applied to the TEST pins for 0.5 seconds.
NOTE: The defrost control board ignores input from the
low-pressure switch terminals as follows:
• During the TEST mode,
• During the defrost cycle,
• During the 90 second start-up period,
•
valve switches heat/cool modes. If the TEST pins are
jumpered and the 5 minute delay is being by-passed,
the LO PS terminal signal is not ignored during the 90
second start-up period.
Diagnostic LEDs
The state (Off, On, Flashing) of two LEDs on the defrost
board (DS1 [Red] and DS2 [Green]) indicate diagnostics
conditions that are described in Table 3.
Mode Green LED (DS2) Red LED (DS1)
No power to control Off Off
Normal operation /
power to control
Anti-short cycle
lockout
Low pressure switch
fault
Off
Low pressure switch
lockout
Off On
High pressure switch
fault
Off
High pressure switch
lockout
On Off
Table 3.
Defrost Board Pressure Switch Connections
The unit’s automatic reset pressure switches (LO PS - S87
and HI PS - S4) are factory-wired into the defrost board on
the LO-PS and HI-PS terminals, respectively.
Low Pressure Switch (LO-PS) — When the low pressure
switch trips, the defrost board will cycle off the compressor,
and the strike counter in the board will count one strike.
The low pressure switch is ignored under the following
conditions:
• during the defrost cycle and 90 seconds after the
termination of defrost
• when the average ambient sensor temperature is
below 15° F (-9°C)
• for 90 seconds following the start up of the compressor
• during “test” mode
High Pressure Switch (HI-PS) — When the high pressure
switch trips, the defrost board will cycle off the compressor,
and the strike counter in the board will count one strike.
Defrost Board Pressure Switch Settings
• High Pressure (auto reset) - trip at 590 psig; reset at
418.
• Low Pressure (auto reset) - trip at 25 psig; reset at 40.
5-Strike Lockout Feature
The internal control logic of the board counts the pressure
switch trips only while the Y1 (Input) line is active. If a
pressure switch opens and closes four times during a Y1
(Input), the control logic will reset the pressure switch trip
counter to zero at the end of the Y1 (Input). If the pressure
the control will enter a lockout condition.
The 5-strike pressure switch lockout condition can be reset
by cycling OFF the 24-volt power to the control board or by
shorting the TEST pins between 1 and 2 seconds. All timer
functions (run times) will also be reset.
If a pressure switch opens while the Y1 Out line is engaged,
a 5-minute short cycle will occur after the switch closes.
Compressor Delay
occasional sounds that may occur while the unit is cycling
in and out of the defrost mode. When a jumper is installed
on the DELAY pins, the compressor will be cycled off for
30 seconds going in and out of the defrost mode. Units are
shipped with jumper installed on DELAY pins.
NOTE: The 30 second compressor delay feature (known
as the quiet shift) must be deactivated during any unit
performance testing. The feature is deactivated by
removing the jumper located on the compressor delay pins
on the control board mounted inside the unit control box.
This feature is optional for the homeowner, but may impact
testing performance.
Loading ...
Loading ...
Loading ...