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System Testing & Troubleshooting
DIAGNOSTIC DISPLAYED REASON FOR DIAGNOSTIC UCM’S REACTION RESET REQUIRED
Saturated Liquid Temperature
Sensor Fail - Circuit 2
(Circuit #2 40-60 Ton units only)
Problem: Circuit 2 Saturated Liquid
Line Temperature sensor input is out
of range.
Check: Sensor resistance between
830 ohms (200 F) and 345.7Kohms
(-40 F). If not, check field/unit wiring
between Sensor and MCM.
The Superheat/Subcool Module is
installed and the unit is reading a
signal that is out of range for the
Circuit 2 Saturated Liquid Line
Temperature Sensor input on the
MCM. (Temp < -40 F or Temp > 200
F).
The Superheat/Subcool
calculation is invalid and the
values are set to zero. No other
change in unit operation occurs.
This diagnostic is for information
only.
(INFO) An automatic reset occurs
after the Circuit 2 Saturated Liquid
Temperature Sensor input returns to
its allowable range. In order to
prevent rapid cycling of the
Diagnostic, there is a 10 second
delay before the automatic reset.
SCM Communications Failure
(20-30 Ton units only)
Problem: The CGM has lost
communications with the SCM.
Check: Check field/unit wiring
between CGM and SCM.
The CGM has lost communications
with the SCM.
A “Lockout” request is sent to the
Compressor Staging Control
function. The Liquid Line
Solenoid Relays and LPC
Bypass Relays are de-
energized. A failsafe function in
the SCM will cause all SCM
outputs to be zeroed and de-
ener
ized.
(PAR) An automatic reset occurs
after communication has been
restored.
Suction Temp Sensor Fail - Circuit 1
Problem: Circuit 1 Suction Line Temp
sensor input is out of range.
Check: Sensor resistance between
830 ohms (200 F) and 345.7Kohms
(-40 F). If not, check field/unit wiring
between Sensor and SCM/MCM.
The Superheat/Subcool Module is
installed and the unit is reading a
signal that is out of range for the
Circuit 1 Suction Line Temp Sensor
input on the SCM/MCM. (Temp < -
40 F or Temp > 200 F).
The Superheat/Subcool
calculation is invalid and the
values are set to zero. No other
change in unit operation occurs.
This diagnostic is for information
only.
(INFO) An automatic reset occurs
after the Circuit 1 Suction Line Temp
Sensor input returns to its allowable
range. In order to prevent rapid
cycling of the Diagnostic, there is a
10 second delay before the
automatic reset.
Suction Temp Sensor Fail - Circuit 2
(Ckt #2 40-60 Ton units only)
Problem: Circuit 2 Suction Line Temp
sensor input is out of range.
Check: Sensor resistance between
830 ohms (200 F) and 345.7Kohms
(-40 F). If not, check field/unit wiring
between Sensor and MCM.
The Superheat/Subcool Module is
installed and the unit is reading a
signal that is out of range for the
Circuit 2 Suction Line Temperature
Sensor input on the MCM. (Temp < -
40 F or Temp > 200 F).
The Superheat/Subcool
calculation is invalid and the
values are set to zero. No other
change in unit operation occurs.
This diagnostic is for information
only.
(INFO) An automatic reset occurs
after the Circuit 2 Suction Line
Temperature Sensor input returns to
its allowable range. In order to
prevent rapid cycling of the
Diagnostic, there is a 10 second
delay before the automatic reset.
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