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During the defrost mode, the reversing valve is energized, the outdoor
fan is de-energized, the compressor is energized, and the defrost con-
trol will provide a 24 V signal from terminal "Wout" to energize electric
heat stage 1, if the unit is so equipped.
For trouble shooting purposes, the defrost cycle can be manually initi-
ated by shorting the "TEST" pins together for 5 s while "Y" is energized.
After removing the short, defrost will terminate normally during the
"TEST" mode.
TEST PINS
STATUS LED
FIGURE 9: Demand Defrost Control
Heat Pump Safety Switch Operation
The unit is equipped with a safety package. The high pressure switch
prevents the pressure in the refrigeration system from becoming too
high. The loss of charge switch protects against loss of charge due to a
leak in the refrigeration system. If either of these safety switches open,
the unit will be shut off for the 5 min anti-short cycle time. Once this has
expired, a 6 h elapsed run timer begins. If a second opening of a safety
switch occurs during this 6 h period, the compressor will be locked out.
Resetting the lockout function is accomplished by:
1. Removing power from the control's thermostat 1st stage (Y) input for
longer than 2 s.
2. Removing power from "R" for more than 2 s.
3. Shorting the "TEST" pins together for more than 2 s while "Y" is
energized.
4. Shorting the "TEST" pins together for more than 5 s while "Y" is de-
energized.
Table 18: Test Pins
Test Pin Shorted
With Y Call
Greater than 2 s
Bypass ASCD
Greater than 5 s
Forced defrost
Johnson Controls Ducted Systems
Table 17: Demand Defrost Selection
*
For extreme environments as necessary only.
Table 19: Fault Codes
Description
High-pressure switch fault (not in lockout yet)
System in high-pressure switch lockout (last mode of
operation was normal compressor)
System in high-pressure switch lockout (last mode of
operation was defrost)
System in loss of charge switch lockout (last mode of
operation was normal compressor)
Low Voltage (<19.2 VAC) preventing further relay
outputs for > 2 s
Low Voltage (<16 VAC) stopped current relay outputs
for > 2 s
Liquid Line sensor failure (Open or Shorted)
Outdoor ambient sensor failure (Open or Shorted)
Control Failure
Without Y Call
Display error codes
Clear error codes
Unit
024 - 060
024 - 060
DEFROST CURVE
SELECTION JUMPER
5020803-UIM-M-0120
Pin Position
2
4*
A0349-001
STATUS LED
2 Flashes
3 Flashes
4 Flashes
5 Flashes
6 Flashes
7 Flashes
8 Flashes
9 Flashes
10 Flashes
17
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