Magic-Pak MHP4 Series, Инструкция по установке и обслуживанию, Страница: 10 / 17

Page 10 of 17 507861-01 Issue 1927
heat stage 2). If a 2-stage thermostat is used, “pigtail” W1
and W2 wires together when connecting the thermostat
wires at the unit.
Defrost Cycle
If the outdoor ambient conditions are such that frost forms
on the outdoor coil, the defrost control monitors the need
for, initiates, and terminates defrost cycles as necessary to
maintain system performance. The defrost control is time/
temperature initiated and temperature terminated with
a maximum defrost time (time-out) of 14 minutes. Time
between defrost cycles is preset at 90-minute intervals at
the factory, but can be field adjusted between 30, 60, or 90
minutes. To field adjust time between defrost cycles, place
defrost time plug in the proper position (see Figure 9).
Figure 8. Defrost Control
24V TERMINAL
STRIP
CONNECTIONS
DIAGNOSTIC
LEDS
HIGH PRESSURE
SWITCH
TEST
PINS
REVERSING
VALVE
DEFROST
THERMOSTAT
LOW PRESSURE
SWITCH
SERVICE LIGHT
CONNECTIONS
FIELD SELECT
DEFROST INTERVAL
TIMING PINS
30
TEST
90
60
P1
Figure 9. Defrost Interval Timing Jumper
Defrost control will initiate a defrost cycle if the time period
has elapsed and the defrost sensor sees a temperature
below freezing. At the start of a defrost cycle, the defrost
control will energize the reversing valve solenoid, shifting
the reversing valve and de-energizing the outdoor fan.
The defrost control will also energize auxiliary heat for
increased comfort during defrost. The unit will remain in
defrost until the defrost sensor has determined that the
frost has been removed from the coil or a 14-minute time
period has elapsed.
The defrost control is also equipped with a set of pins to aid
in the troubleshooting of the defrost system (see Figure 9).
The following is a brief outline of the testing of the defrost
system.
1. Defrost sensor must be closed, 32°F or below. If
temperatures are such that the switch will not close,
jumper between defrost sensor terminals on the
defrost control.
2. Start system in heating operation.
3. Place the defrost pin jumper on the test pins for a brief
second, then place back on the proper defrost time
setting (30, 60, or 90). This will speed up defrost time
interval as shown in Table 7.
Defrost Control Setting Defrost Test Cycle Time
30 minutes 7 seconds
60 minutes 14 seconds
90 minutes 21 seconds
Table 7. Defrost Test Cycle Time
The reversing valve will then shift to defrost mode and
the outdoor fan should stop. After 2 seconds of defrost
operation, the reversing valve should shift back to heating
operation and the outdoor fan should start.
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 8.
Mode Green LED (DS2) Red LED (DS1)
No power to control Off Off
Normal operation /
power to control
Simultaneous slow flash
Timed lockout Alternating slow flash
Low pressure switch
fault
Off Slow flash
Low pressure switch
lockout
Off On
High pressure switch
fault
Slow flash Off
High pressure switch
lockout
On Off
Table 8.