ZN010, ZN510, and ZN520 Controllers
142 UNT-SVX07E-EN
Electric Heat
Fresh Air Damper
Table 82. Valves remain 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 the current step in the test sequence, the valves may be open. Refer
to the “Manual Output Test,” page 137.
Diagnostic present A specific list of diagnostics affects valve operation. For more information, see Ta bl e 7 8 and Table 79, page 140.
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 “Water Temperature Sampling Function,” page 116.
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 unit wiring diagrams on the unit.
Table 83. Electric heat not operating
Probable Cause Explanation
Normal operation The controller cycles electric heat on and off to meet the unit capacity requirements.
Requested mode: off
It is possible to communicate the operating mode (such as off, heat, cool) to the controller. When off is
communicated to the controller, the units shuts off the electric heat.
Communicated disable
Numerous communicated requests may disable electric heat, including an auxiliary heat enable input and the heat/
cool mode input. Depending on the state of the communicated request, the unit may disable electric heat.
Manual output test
The controller includes a manual output test sequence that verifies analog and binary output operation and
associated output wiring. However, based on the current step in the test sequence, the electric heat may not be
on. Refer to “Manual Output Test,” page 137.
Diagnostic present
A specific list of diagnostics affects electric heat operation. For more information, see “Diagnostics and
Troubleshooting,” page 129.
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 electric heat may not work properly.
No power to the controller
If the controller does not have power, electric heat does not operate. For the controller to operate normally, a 24 Vac
input voltage must be applied. When the green LED is off continuously, the controller does not have sufficient power
or has failed.
Unit wiring
The wiring between the controller outputs and the electric heat contacts must be present and correct for normal
electric heat operation. Refer to the unit wiring diagrams on the unit.
ECM motor/Motor control
board failure
ECM controls include sophisticated fan proving / interlock circuitry that will disable electric heat if one or more
motors are not performing normally
Hot water is present on a
changeover unit
On units with changeover coil and electric heat, simultaneous operation of hydronic heat and electric heat is not
allowed.
Table 84. Fresh air damper stays open
Probable Cause Explanation
Normal operation
The controller opens and closes the fresh air damper based on the controller’s occupancy mode and fan status.
Normally, the fresh air damper is open during occupied mode when the fan is running and closed during unoccupied
mode.
Manual output test
The controller includes a manual output test sequence that verifies analog and binary output operation and associated
output wiring. However, based on the current step in the test sequence, the fresh air damper may not be open. Refer
to “Manual Output Test,” page 137.
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 damper may not work correctly.
Unit wiring
The wiring between the controller outputs and the fresh air damper must be present and correct for normal damper
operation. Refer to the unit wiring diagrams on the unit.
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