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Trouble Shooting
Clogged Filter Switch
This LED will remain lit the entire
time that the Normally Open switch
is closed. The LED will be turned off
immediately after resetting the
switch (to the Normally Open
position), or any time that the IDM is
turned "Off" .
If the switch remains closed, and the
IDM is turned "On" , the SERVICE LED
will be turned "On" again after the 2
(±1) minute ignore delay.
This LED being turned "On" , will have
no other affect on unit operation. It is
an indicator only.
Fan Failure Switch
When the "Fan Failure" switch is
wired to the RTOM, the LED will
remain flashing the entire time the
fan proving switch is closed,
indicating a fan failure, and it will
shut the unit operations down.
Zone Temperature Sensor
(ZTS) Test
Note: These procedures are not for
programmable or digital
models and are conducted
with the Zone Sensor Module
electrically removed from the
system.
Test 1 - Zone Temperature
Thermistor (ZTEMP)
This component is tested by
measuring the resistance between
terminals 1 and 2 on the Zone
Temperature Sensor. Below are some
typical indoor temperatures, and
corresponding resistive values.
RT-SVX21F-EN
Test 2 - Cooling Set Point
(CSP) and Heating Set Point
(HSP)
Table 13.
Cooling setpoint and heating
setpoint
Nominal ZTEMP
Zone Temperature
Resistance
50 F°
10.0 C°
19.9 K-Ohms
55 F°
12.8 C°
17.47 K-Ohms
60 F°
15.6 C°
15.3 K-Ohms
65 F°
18.3 C°
13.49 K-Ohms
70 F°
21.1 C°
11.9 K-Ohms
75 F°
23.9 C°
10.50 K-Ohms
80 F°
26.7 C°
9.3 K-Ohms
85 F°
29.4 C°
8.25 K-Ohms
90 F°
32.2 C°
7.3 K-Ohms
The resistance of these
potentiometers are measured
between the following ZSM
terminals. Refer to the chart above
for approximate resistances at the
given setpoints.
Cool SP = Terminals 2 and 3
Range = 100 to 900 Ohms
approximate
Heat SP = Terminals 2 and 5
Range = 100 to 900 Ohms
approximate
Test 3 - System Mode and Fan
Selection
The combined resistance of the
Mode selection switch and the Fan
selection switch can be measured
between terminals 2 and 4 on the
Zone Sensor. The possible switch
combinations are listed below with
their corresponding resistance
values.
Test 4 - LED Indicator Test,
(SYS ON, HEAT, COOL &
SERVICE)
Method 1
Testing the LED using a meter with
diode test function. Test both forward
and reverse bias. Forward bias
should measure a voltage drop of 1.5
to 2.5 volts, depending on your
meter. Reverse bias will show an
Over Load, or open circuit indication
if LED is functional.
Method 2
Testing the LED with an analog
Ohmmeter. Connect Ohmmeter
across LED in one direction, then
reverse the leads for the opposite
direction. The LED should have at
least 100 times more resistance in
reverse direction, as compared with
the forward direction. If high
resistance in both directions, LED is
open. If low in both directions, LED is
shorted.
Method 3
To test LED's with ZSM connected to
unit, test voltages at LED terminals
on ZSM. A measurement of 32 VDC,
across an unlit LED, means the LED
has failed.
Relative Humidity Sensor Test
This component is measured by
measuring the mA output signal on
the Relative Humidity Sensor. Verify
accuracy of the sensor annually. If
the output reading is 0 mA, first
verify that power is applied to the
sensor. A reading of 4 mA
corresponds to 0% RH and 20 mA
corresponds to 100% RH.
% RH
mA
30
8.8
40
10.4
50
12.0
60
13.6
70
15.2
80
16.8
Note: Measurements should be
made from LED common
(ZSM terminal 6 to respective
LED terminal). Refer to the
Zone Sensor Module (ZSM)
Terminal Identification table
at the beginning of this
section.
Programmable & Digital Zone
Sensor Test
Testing serial communication voltage
1.
Verify 24 VAC is present between
terminals J6-14 & J6-11.
2.
Disconnect wires from J6-11 and
J6-12. Measure the voltage
between J6-11 and J6-12, should
be about 32 VDC.
47
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Troubleshooting
