43
Residential Packaged Units - 60Hz Puron
®
Rev.: 4 Jan., 2012
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 “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 verifi ed, board operation is confi rmed 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 verifi ed
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 verifi ed 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 fi ve
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” 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!
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