Pinpoint Test L: The Air Conditioning (A/C) Is Always On
Refer to Wiring Diagrams Cell
55
, Automatic Climate Control System for schematic and connector information.
Normal Operation
Under normal operation, when A/C is requested, a message is sent over the bus from the electronic automatic temperature control (EATC) module, through the instrument cluster, to the
powertrain control module (PCM). The PCM receives input from the A/C cycling switch through circuit 883 (PK/LB). Voltage is provided to the A/C cycling switch through circuit 1040
(RD/BK)/348 (VT).
The PCM provides a ground for the A/C clutch relay coil through circuit 73 (OG/LB). The A/C clutch relay coil receives voltage through circuit 391 (RD/YE). Voltage for the A/C clutch relay
switch is provided through circuit 1810 (LG/OG). When the relay is activated, voltage is supplied to the A/C clutch solenoid through circuit 321 (GY/WH). Ground is supplied for the A/C
clutch through circuit 57 (BK).
The A/C cycling switch is used for A/C compressor cycling. The switch is used by the PCM to turn off the A/C compressor before the line pressures are low enough to drop the evaporator
temperature to low and freeze the condensation.
When an A/C request is received by the PCM, the A/C compressor clutch will only be engaged through the A/C clutch relay if all of the following conditions are met:
The PCM does not detect excessively high or low refrigerant pressure from the A/C pressure transducer.
The PCM does not detect excessively low refrigerant pressure from the A/C cycling switch.
The PCM does not detect excessively high engine coolant temperature.
The PCM does not detect an ambient air temperature too low.
The PCM has not detected a Wide Open Throttle (WOT) condition.
Possible Causes
Wiring, terminals or connectors
A/C pressure transducer
PCM
A/C clutch relay
Electronic automatic temperature control (EATC) module
A/C clutch air gap
PINPOINT TEST L: THE AIR CONDITIONING (A/C) IS ALWAYS ON
NOTE:
Before carrying out the following test, diagnose any PCM or instrument cluster DTCs.
Is the resistance less than 5 ohms?
K16 CHECK THE HVAC MODULE CONNECTION
Inspect the module connectors for:
corrosion.
pushed-out terminals.
damaged terminals.
Connect and correctly seat all the HVAC module connectors.
Clear the DTCs.
Operate the system and verify the concern is still present.
Is the concern still present?
Yes
INSTALL a new HVAC module. REFER to
Section 412-01
. TEST the system for normal
operation.
No
The system is operating correctly at this time.
The concern may have been caused by a loose
or corroded connector. CLEAR the DTCs.
REPEAT the self-test. TEST the system for
normal operation.
K17 CHECK THE PCM CONNECTION
Disconnect all the PCM connectors.
Inspect the module connectors for:
corrosion.
pushed-out terminals.
damaged terminals.
Connect and correctly seat all the PCM connectors.
Clear the DTCs.
Operate the system and verify the concern is still present.
Is the concern still present?
Yes
INSTALL a new PCM. TEST the system for
normal operation.
No
The system is operating correctly at this time.
The concern may have been caused by a loose
or corroded connector.
Page 34 of 45
2006 Town Car Workshop Manual
12/30/2011
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