Page 19
Defrost System
Low Pressure Switch
The HPXA12 is equipped with an auto−reset low pressure
switch which is located on the vapor line. The switch shuts
off the compressor when the vapor pressure falls below the
factory setting. This switch is ignored during defrost opera-
tion and when the outdoor temperature goes below 15°F.
The switch closes when it is exposed to 60 psig and opens
at 25 psig. It is not adjustable.
High Pressure Switch
The HPXA12 is equipped with an auto−reset high pressure
switch (single−pole, single−throw) which is located on the
liquid line. The switch shuts off the compressor when dis-
charge pressure rises above the factory setting. The switch
is normally closed and is permanently adjusted to trip
(open) at 640 + 10 psig (4412 + 69 kPa).
NOTE − A Schrader core is under the pressure switches.
HPXA12 Defrost Control Board
Figure 17
24V terminal strip
connections
diagnostic LEDs
pressure switch
circuit connections
defrost interval
timing pins
Note − Component Locations Will Vary With Board Manufacturer
ambient
sensor
coil
sensor
field select
temperature pins
Y2
Y2
DELAY
reversing valve
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