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62 UNT-SVX07A-EN
Maintenance
diagnostics
Table M-D-3. Fan outputs do not energize
Probable Cause Explanation
Random start After power-up, the controller always observes a random start that varies observedbetween 0 and 25 seconds. The controller
remains off until the random start time expires.
Power-up control wait When power-up control wait is enabled (non-zero time), the controller remains off until one of two conditions occurs:
1. The controller exits power-up control wait once it receives communicated information.
2. The controller exits power-up control wait once the power-up control wait time expires.
Cycling fan operation When the fan mode switch is in the auto postion, the unit fan cycles off when there is no call for heating or cooling. The heating/
cooling sources cycle on oroff periodically with the unit fan to match the capacity according to pulse-width-modulation (PWM) logic.
Unoccupied operation The fan cycles with capacity when the unit is in unoccupied mode. This occurs even if the unit is in continuous fan operation. While
unoccupied, the fan cycleson or off with heating/cooling to provide varying amounts of heating or cooling to the space. to match the
capacity according to pulse-width-modulation (PWM) logic.
Fan mode off When using the local fan mode switch to determine the fan operation, the off position controls the unit fan to off.
Requested mode: off It is possible to communicate the operating mode (such as off, heat, and cool) to the controller. When “off” is communicated to the
controller, the unitcontrols the fan to off. The unit is not capable of heating or cooling when the controller is in this mode.
Diagnostic present A specific list of diagnostics effects fan operation. For more information, see the “Diagnostics” section.
No power to the If the controller does not have power, the unit fan will not operate. For the controller controller to operate
controller normally, it must have an input voltage of 24 VAC. Whenthe green LED is off continuously, the controller does not have sufficient
power or the controller has failed.
Manual output test The controller includes a manual output test sequence to verify binary output operation and the associated wiring. However, based
on the current step in the test sequence, the unit fan may not be powered on. Refer to the “Manual Output Test” section.
Unit wiring The wiring between the controller outputs and the fan relays and contacts must be present and correct for normal fan operation.
Refer to the typical unit wiringdiagrams in the Appendix of this manual.
Table M-D-4. Valves Stay Closed
Probable Cause Explanation
Normal operation The controller opens and closes the valves to meet the unit capacity requirements.
Requested mode: off It is possible to communicate the operating mode (such as off, heat, and cool) to the controller. When off is communicated to the
controller, the unitcontrols the fan to off. The unit is not capable of heating or cooling when the controller is in this mode.
Valve override The controller can communicate a valve override request. This request effects the valve operation.
Manual output test The controller includes a manual output test sequence to verify analog and binary output operation and the associated wiring.
However, based on thecurrent step in the test sequence, the valves may not be open. Refer to the “Manual Output Test” section.
Diagnostic present A specific list of diagnostics affects valve operation. For more information, see the “Diagnostics” section.
Sampling logic The controller includes entering water temperature sampling logic that automatically invokes during 2-pipe or 4-pipe changeover. It
determines whenthe entering water temperature is either too cool or too hot for the desired heating or cooling mode. Refer to the
“Entering Water section.
Unit configuration The controller must be properly configured based on the actual installed end devices and application. When the unit configuration
does not match the actualend device, the valves may not work correctly.
No power to the If the controller does not have power, the valves do not operate. For the controller controller to operate normally,
it must have an input voltage of 24 VAC. When the green LED is off continuously, the controller does not have sufficient power,or the
controller has failed.
Unit wiring The wiring between the controller outputs and the valve(s) must be present and correct for normal valve operation. Refer to the
typical unit wiring diagrams in the Appendix of this manual.
Table M-D-5. Valves Stay Open
Probable Cause Explanation
Normal operation The controller opens and closes the valves to meet the unit capacity requirements.
Valve override The controller can communicate a valve override request to affect the valve operation.
Manual output test The controller includes a manual output test sequence that verifies analog and binary output operation and the associated wiring.
However, based on thecurrent step in the test sequence, the valves may be open. Refer to the “Manual Output Test” section.
Diagnostic present A specific list of diagnostics affects valve operation. For more information, see the “Diagnostics” section.
Sampling logic The controller includes entering water temperature sampling logic that automatically invokes during 2-pipe or 4-pipe
changeover to determine if the entering water temperature is correct for the unit operating mode. Refer to the “Entering Water
Temperature Sampling” section.
Unit configuration The controller must be properly configured based on the actual installed end devices and application. When the unit configuration does
not match the actual end device, the valves may not work correctly.
Unit wiring The wiring between the controller outputs and the valve(s) must be present and correct for normal valve operation. Refer to the
typical unit wiring diagrams inthe Appendix of this manual.