Installation, Operation & Maintenance | HEV/H SERIES | Heat Controller, Inc. |
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TROUBLESHOOTING
General
If operational difficulties are encountered, perform the preliminary checks below before referring to the troubleshooting charts.
•Verify that the unit is receiving electrical supply power.
•Make sure the fuses in the fused disconnect switches are intact.
After completing the preliminary checks described above, inspect for other obvious problems such as leaking connections, broken or disconnected wires, etc. If everything appears to be in order, but the unit still fails to operate properly, refer to the “DXM2 Troubleshooting Process Flowchart” or “Functional Troubleshooting Chart.”
DXM2 Board
DXM2 board troubleshooting in general is best summarized as verifying inputs and outputs. After inputs and outputs have been verified, board operation is confirmed and the problem must be elsewhere. Below are some general guidelines for troubleshooting the DXM2 control.
Field Inputs
Conventional thermostat inputs are 24VAC from the thermostat and can be verified using a voltmeter between C and Y1, Y2, W, O, G. 24VAC will be present at the terminal (for example, between “Y1” and “C”) if the thermostat is sending an input to the DXM2 board.
Proper communications with a thermostat can be verified using the Fault LED on the DXM2. If the control is NOT in the Test mode and is NOT currently locked out or in
a retry delay, the Fault LED on the DXM2 will flash very slowly (1 second on, 5 seconds off), if the DXM2 is properly communicating with the thermostat.
Sensor Inputs
All sensor inputs are ‘paired wires’ connecting each component to the board. Therefore, continuity on pressure switches, for example can be checked at the board connector. The thermistor resistance should be measured with the connector removed so that only the impedance of the thermistor is measured. If desired, this reading can be compared to the thermistor resistance chart shown in the DXM2 AOM manual. An ice bath can be used to check the calibration of the thermistor.
Outputs
The compressor and reversing valve relays are 24VAC and can be verified using a voltmeter. For units with PSC blower motors, the fan relay provides a contact closure to directly power the blower motor, or provide 24VAC to an external fan relay. For units with ECM blower motors, the DXM2 controls the motor using serial communications, and troubleshooting should be done with a communicating thermostat or diagnostic tool. The alarm relay can either be 24VAC as shipped or dry contacts for use with DDC controls by clipping the JW1 jumper. Electric heat outputs are 24VDC “ground sinking” and require a voltmeter set for DC to verify operation. The terminal marked “24VDC” is the
24VDC supply to the electric heat board; terminal “EH1” is stage 1 electric heat; terminal “EH2” is stage 2 electric heat. When electric heat is energized (thermostat is sending a “W” input to the DXM2 controller), there will be 24VDC between terminal “24VDC” and “EH1” (stage 1 electric heat) and/or “EH2” (stage 2 electric heat). A reading of 0VDC between “24VDC” and “EH1” or “EH2” will indicate that the DXM2 board is NOT sending an output signal to the electric heat board.
Test Mode
Test mode can be entered for 20 minutes by pressing the Test pushbutton. The DXM2 board will automatically exit test mode after 20 minutes.
Advanced Diagnostics
If a communicating thermostat or diagnostic tool is connected to the DXM2, additional diagnostic information and troubleshooting capabilities are available. The current status of all DXM2 inputs can be verified, including the current temperature readings of all temperature inputs. With a communicating thermostat the current status of the inputs can be accessed from the Service Information menu. In the manual operating mode, most DXM2 outputs can be directly controlled for system troubleshooting. With a communicating thermostat the manual operating mode can be accessed from the Installer menu. For more detailed information on the advanced diagnostics of the DXM2, see the DXM2 Application, Operation and Maintenance (AOM) manual (part #97B0003N15).
DXM2 Troubleshooting Process Flowchart/Functional Troubleshooting Chart
The “DXM2 Functional Troubleshooting Process Flowchart” is a quick overview of how to start diagnosing a suspected problem, using the fault recognition features of the DXM2 board. The “Functional Troubleshooting Chart” on the following page is a more comprehensive method for identifying a number of malfunctions that may occur, and is not limited to just the DXM2 controls. Within the chart are five columns:
•The “Fault” column describes the symptoms.
•Columns 2 and 3 identify in which mode the fault is likely to occur, heating or cooling.
•The “Possible Cause column” identifies the most likely sources of the problem.
•The “Solution” column describes what should be done to correct the problem.
WARNING!
WARNING! HAZARDOUS VOLTAGE! DISCONNECT ALL ELECTRIC POWER INCLUDING REMOTE DISCONNECTS BEFORE SERVICING.
Failure to disconnect power before servicing can cause severe personal injury or death.
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