Trane TTA240F Series Installation Operation & Maintenance page 21

Temperature Tests
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 can be 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.
Zone Nominal
Temperature Resistance
50°F or 10.0°C 19.9 Kohms
55°F or 12.8°C 17.47 Kohms
60°F or 15.6°C 15.3 Kohms
65°F or 18.3°C 13.49 Kohms
70°F or 21.1°C 11.9 Kohms
75°F or 23.9°C 10.50 Kohms
80°F or 26.7°C 9.3 Kohms
85°F or 29.4°C 8.25 Kohms
90°F or 32.2°C 7.3 Kohms
Test 2 - Cooling Set Point (CSP)
and Heating Set Point (HSP)
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.
TTA-SVN03A-EN
Troubleshooting
ReliaTel™ Controls
Test 4 - LED Indicator Test, (SYS
ON, HEAT, & COOL)
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.
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.
3. Reconnect wires to terminals J6-
11 and J6-12. Measure voltage
again between J6-11 and J6-12,
voltage should flash high and low
every 0.5 seconds. The voltage on
the low end will measure about
19 VDC, while the voltage on the
high end will measure from
approximately 24 to 38 VDC.
4. Verify all modes of operation, by
running the unit through all of the
steps in the "Test Modes" section
discussed in "Unit Start-Up" .
5. After verifying proper unit
operation, exit the test mode.
Turn the fan on continuously at
the ZSM, by pressing the button
with the fan symbol. If the fan
comes on and runs continuously,
the ZSM is good. If you are not
able to turn the fan on, the ZSM is
defective.
RTCI Loss of communications
If the RTCI loses input from the
building management system, the
RTRM will control in the default mode
after approximately 15 minutes. If the
RTRM loses the Heating and Cooling
setpoint input, the RTRM will control
in the default mode instantaneously.
The temperature sensing thermistor
in the Zone Sensor Module is the only
component required for the "Default
Mode" to operate.
21