HP - C 2
Electronic Expansion Valve (EEV) Test
Overview
Some communicating system heat pumps use a spe-
cial expansion valve called an EEV (Figure 1) in the
outdoor unit.
The EEV adjusts its internal orifice size in small incre-
ments via commands from the EEV board. The EEV
stepper motor coil connects to the circuit board at
connector J1.
Two sensors provide input information to the EEV
control board. The board has a suction pressure
transducer and a suction line temperature sensor.
These sensors provide the board the needed informa-
tion to calculate operating suction vapor superheat.
Based upon the values received from these sensors,
the EEV board will adjust the flow of refrigerant into
the outdoor coil during heat mode to provide superior
control of operational superheat.
Problems
The EEV control board has two LED’s that flash to
indicate operational status and faults. The GREEN
LED is the STATUS LED and the RED LED is the
FAULT LED.
Figure 1
This expansion valve operates at half open during
cool mode and adjusts to a larger or smaller step po-
sition to provide refrigerant metering capability in heat-
ing mode. The operation of the valve is controlled by a
circuit board located in the outdoor unit. The EEV
board (Figure 2) receives its power from the 24 volt
transformer located in the outdoor unit on plug J6.
Figure 2
J6
J1
Control Input
24 VAC Stage/Mode
To Coil on EEV
Status LED
Red
Fault LED
Green
Test Pins
- Test
- Open
- Close
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