Installation, Operation & Maintenance | HTV/HTD/HTH SERIES | Heat Controller, Inc. |
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 “CXM Troubleshooting Process Flowchart” or “Functional Troubleshooting Chart.”
CXM Board
CXM board troubleshooting in general is best summarized as simply 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 CXM control.
Field Inputs
All inputs are 24VAC from the thermostat and can be verified using a volt meter between C and Y, G, O, W. 24VAC will be present at the terminal (for example, between “Y” and “C”) if the thermostat is sending an input to the CXM board.
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 CXM AOM manual. An ice bath can be used to check calibration of the thermistor.
Outputs
The compressor relay is 24VAC and can be verified using a voltmeter. The fan signal is passed through the board to the external fan relay (units with PSC motors only). 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 volt meter 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 CXM 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 CXM board is NOT sending an output signal to the electric heat board.
Test Mode
Test mode can be entered for 20 minutes by shorting the test pins. The CXM board will automatically exit test mode after 20 minutes.
CXM Troubleshooting Process Flowchart/Functional Troubleshooting Chart
The “CXM Functional Troubleshooting Process Flowchart” is a quick overview of how to start diagnosing a suspected problem, using the fault recognition features of the CXM 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 CXM controls. Within the chart are five columns:
•The “Fault” column describes the symptoms.
•Columns 2 and 3 identify in which mode the fault is likey 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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