Comfort-Aire HEH Series 2 to 5 Tons - Manual (Page 40)

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Installation, Operation & Maintenance HEV/H SERIES Heat Controller, LLC.
General
If operational diffi culties 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 verifi ed, board operation is confi rmed 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 verifi ed 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 verifi ed
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 fl ash 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 verifi ed 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 verifi ed, 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
fi ve 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” identifi es the most likely
sources of the problem.
• The “Solution” column describes what should be done to
correct the problem.
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.
TROUBLESHOOTING
WARNING!