Multi-Zone Technical Overview

TESTING
PAGE 29
ENGLISH
OUTDOOR UNIT TESTING PROCEDURES
Temperature sensor testing
The temperature sensors are negative coecient type. These
sensors will reduce their electrical resistance as temperature
decreases. Should the sensors fail, the ECU will generate an
appropriate Error Code.
To check the calibration of the sensors:
1. Shut o power to the outdoor unit.
2. Disconnect the sensor at the circuit board plug.
3. Measure the temperature of the air surrounding the
sensor.
4. Measure the electrical resistance of the sensor. Do
not force leads into sensor plug.
5. Compare the measured resistance of the sensor
against the specication resistance/temperature
limit listed in the reference table in this manual.
6. If the sensor resistance is outside of the specication
tolerances shown on the resistance/temperature
table, replace the sensor.
Restricted/Sticking Outdoor Unit Check Valve Test
The Check Valve allows refrigerant to ow freely around the
outdoor unit heat mode EEV during cooling mode. The valve is
a one directional device. The check valve has an internal steel
ball that will allow refrigerant to bypass or it will backseat and
block refrigerant ow.
In heating mode this valve will backseat to force liquid
refrigerant to ow into and through the Heat Mode EEV.
If the check valve sticks, the refrigeration cycle will experience
malfunction. Depending upon the mode of operation, a
sticking check valve may bypass the outdoor EEV and ood
the outdoor coil, or it may force liquid refrigerant through the
outdoor EEV during heating mode and cause a restriction.
How to test a check valve
1. With the system running in cooling mode, the
valve should ow refrigerant freely past the EEV. Take
the temperature of the liquid entering and leaving
the check valve. If there is a large temperature drop,
the check valve is partially restricted. If the
temperature of the liquid refrigerant into and out of
the check valve are the same, the valve is freely
owing liquid. If the valve is restricted, replace it.
2. In heating mode, the valve should block refrigerant
ow and force the liquid into the outdoor unit
Heating Mode EEV. Check the temperature of the
liquid entering and leaving the check valve. If the
valve is working properly, there should be warm liquid
at the entrance to the valve and cold refrigerant at
the exit. If there is no temperature dierence, the
valve is allowing liquid to bypass the EEV. Replace the
check valve.