31
TROUBLESHOOTING UNITS FOR PROPER
SWITCHING BETWEEN LOW & HIGH
STAGES
Check the suction pressures at the service valves. Suction pressure
should be reduced by 3--10% when switching from low to high
capacity.
Compressor current should increase 20 to 45% when switching
from low to high stage. The compressor solenoid when energized
in high stage, should measure 24VAC across pin numbers PL5--2
HI and PL5--5 C . When the compressor is operating in low stage,
the 24V DC compressor solenoid coil is de--energized. When the
compressor is operating in high stage, the 24V DC solenoid coil is
energized.
The solenoid plug harness that is connected to the compressor has
an internal rectifier that converts the 24V AC signal to 24V DC.
DO NOT INSTALL A PLUG WITHOUT AN INTERNAL
RECTIFIER
.
Unloader Test Procedure
The unloader is the compressor internal mechanism, controlled by
the DC solenoid, that modulates between high and low stage. If it
is suspected that the unloader is not working, the following
methods may be used to verify operation.
1. Operate the system and measure compressor amperage. Cy-
cle the unloader on and off at 30 second plus intervals at the
User Interface (from low to high stage and back to low
stage). Wait 5 seconds after staging to high before taking a
reading. The compressor amperage should go up or down
at least 20 percent.
2. If the expected result is not achieved, remove the solenoid
plug from the compressor and with the unit running and the
User Interface or thermostat calling for high stage, test the
voltage output at the plug with a DC voltmeter. The read-
ing should be 24 volts DC.
3. If the correct DC voltage is at the control circuit molded
plug, measure the compressor unloader coil resistance. The
resistance should be approximately 330 or 1640 ohms de-
pending on unloader coil supplier. If the coil resistance is
infinite or is grounded, the compressor must be replaced.
Two Stage Compressor
The two stage compressor contains motor windings that provide
2--pole (3500 RPM) operation.
Compressor Internal Relief
The compressor is protected by an internal pressure relief (IPR)
which relieves discharge gas into the compressor shell when
differential between suction and discharge pressure exceeds
550--625 psi. The compressor is also protected by an internal
overload attached to motor windings.
Compressor Control Contactor
The contactor has a 24volt coil. The electronic control board
controls the operation of the contactor.
Troubleshoot Compressor
If the compressor fails to operate, Table 16 can be used to verify if
there is any damage to the compressor windings causing system
malfunction.
Table 16 – Winding Resistance
Compressor Ohms
Model
Start Winding
Run Winding
GZ024
1.64
1.3
GZ036
1.52
0.88
GZ048
1.86
0.52
GZ060
1.63
0.39
GZ072 1.85
0.34
Tol/- 7%. All resistance values must be measured with
compressor at room temperature.
Systems Communication Failure
If communication with the compressor control is lost with the
Communicating System Wall Control, the control will flash the
appropriate fault code (see Table 15) to the rest of the
communicating system, including the wall control and the indoor
split geothermal unit.
Model Plug
Each control board contains a model plug. The model plug is used
to identify the type and size of unit to the control.
The correct model plug must be installed for the system to operate
properly (see Table 17).
Table 17 – Model Plug Information
Model
Model Plug
Number
Pins 1---4
Pins 2---3
GZ024
HK70EZ001
5.1K
11K
GZ036
HK70EZ002
5.1K
18K
GZ048
HK70EZ003
5.1K
24K
GZ060
HK70EZ004
5.1K
33K
GZ072
HK70EZ005
5.1K
39K
On new units, the model and serial numbers are input into the
board’s memory at the factory. If a model plug is lost or missing at
initial installation, the unit will operate according to the
information input at the factory and the appropriate error code will
flash temporarily.
NOTE
: RCD replacement boards contain no model and serial
information. If the factory control board fails, the model plug must
be transferred from the original board to the replacement board for
the unit to operate.
NOTE
:
The model plug takes priority over factory model
information input at the factory. If the model plug is removed after
initial power up, the unit will operate according to the last valid
model plug installed, and flash the appropriate fault code
temporarily.
Troubleshooting the Model Plug
If the unit is being identified incorrectly by model or size, verify
the plug resistance per Table 17. If resistance value verifies the
plug is good, ensure the plug is dry and condensate free.
NOTE
: Dielectric grease (field supplied) can be used on model
plug pins if condensate has been noted after drying the plug.
