Troubleshooting
RT-SVX21AC-EN 79
Unit Economizer Control (ECA)
Test Procedures
Electromechanical Control
This series of tests will allow you to diagnose, and
determine where, and if a problem exists in the system
economizer operation. Test 1 determines if the problem is
in the Unit, or if it is in the ECA. Test 2 tests sensor inputs.
Test 3 tests the resistors and sensors. Conduct the tests in
numerical order until problem is found.
Test 1
Verifying that the economizer actuator (ECA) is functional:
1. Using the “Test Mode” described in the “System Start-
Up” section, pu
t the unit into the economizer mode
and verify that the economizer actuator (ECA) drives
fully open (approximately 90 seconds).
2. If the ECA is not driving the
da
mpers, verify that 24 Vac
is between the ECA terminals TR and TR1 is present. If
24 volts is not present, a wiring or terminal problem
exists from the control transformer. Make any
necessary repairs, see wiring diagrams to
troubleshoot.
3. If 24 Vac is present, adj
ust the minimum position
potentiometer fully clockwise. If the actuator does not
drive, the economizer actuator is bad. Replace the ECA.
Test 2
Testing the ECA resistors and sensors
1. Testing the Mixed Air Sensor (MAS). Disconnect the
wires conn
ected to T and T1 on the ECA, and;
a. Measure the resistance of the sensor between the
wires
180B an
d 181B.
b. Measure the temperature at the MAS location.
Using the Tem
perature versus Resistance chart,
verify the accuracy of the MAS.
Replace the sensor if it is out of range.
2. Testing the Outdoor Air Switch. If the temperature is
abo
ve 60 degrees, it will need to be chilled. Measure
the resistance of the sensor on the ECA SO and +.
The resistance should be approximately 390 Ohms.
Replace the Switch if it is open.
Replace the ECA if it is out of range.
3. Testing the R1 Resistance.
Measure the resistance of th
e sensor on
the ECA SR
and +.
The resistance should be approximately 420 Ohms.
Replace the ECA if it is out of range.
4. Testing the R2 Resistance.
Measure the resistance of the sensor on the ECA P and
P1
.
The
resistance should be approximately 130 Ohms.
Replace the ECA if it is out of range.
Troubleshooting procedures for
Direct Drive Plenum Fan
Prior to troubleshooting, verify all wiring and wiring
connections. The motor has internal protections that will
shut down the motor before damage occurs. A power
cycle is required to reset some of the internal protections.
Before proceeding, power down unit for 1 minute and then
power on.
Please follow steps sequentially unless directed
di
fferently in
solution.
Refer to RT-SVP08*-EN for a Com
pre
hensive
Troubleshooting Guide.
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