Chrysler PT Cruiser, Service & Repair Manual, Page: 1925 / 2078

A/C LOW PRESSURE SWITCH
DESCRIPTION
The A/C low pressure switch is a single pole, single
throw, pressure actuated switch that is installed in a
threaded port into the suction passage of the accu-
mulator. The switch is located on the top of the accu-
mulator in a fitting that contains a Schrader type
valve, which allows the switch to be serviced without
discharging the refrigerant system. The accumulator
fitting is equipped with a O-ring to seal the switch
plumbing connection.
The A/C low pressure switch is a factory calibrated
unit. The switch cannot be adjusted or repaired and
if faulty or damaged it must be replaced.
OPERATION
The A/C low pressure switch monitors the pressure
of the refrigerant leaving the accumulator to the
compressor. The switch is connected in series electri-
cally with the heater-A/C control blower and mode
switches and the high pressure cut out switch
between ground and the Powertrain Control Module
(PCM). The switch contact open or close the path the
ground, signaling the PCM to turn the compressor
clutch on and off. This regulates the refrigerant sys-
tem pressure and controls evaporator temperature.
Controlling the evaporator temperature prevents con-
densate water on the evaporator fins from freezing
and obstructing air conditioning system air flow.
The A/C low pressure switch contacts are open
when the suction pressure is approximatly 152 kPa
(22 psi) or lower. The switch contacts will close when
the suction pressure rises to approximately 234 to
262 kPa (34 to 38 psi) or above. Lower temperatures,
below approximately -1° C (30° F), will also cause the
switch contacts to open. This is due to the pressure/
temperature relationship of the refrigerant in the
system.
DIAGNOSIS AND TESTING - A/C LOW
PRESSURE CLUTCH CYCLING SWITCH
Before performing diagnosis of the low pressure
clutch cycling switch, be certain that the switch is
properly installed on the accumulator fitting. If the
switch is too loose it may not open the Schrader-type
valve in the accumulator fitting, which will prevent
the switch from correctly monitoring the refrigerant
system pressure.
Also verify that the refrigerant system had the cor-
rect refrigerant charge(Refer to 24 - HEATING &
AIR CONDITIONING - STANDARD PROCEDURE).
(1) With gear selector in park or neutral and park
brake set, start engine and allow to idle.
(2) Raise hood and disconnect low pressure cut off
switch connector boot.
(3) Using a suitable jumper wire, jump across the
terminals inside wire connector boot.
(4) If the compressor clutch does not engage, the
cycling clutch switch, wiring, relay, or fuse can be
defective (Refer to 8 - ELECTRICAL/WIRING DIA-
GRAM INFORMATION - DIAGNOSIS AND TEST-
ING).
(5) If clutch engages, connect manifold gauge set.
Read low pressure gauge. At pressure above 97 kPa
(14 psi) and above, low pressure out off switch will
complete the clutch circuit. If the low pressure gauge
reads below 140 kPa (20 psi), the system is low on
refrigerant charge or empty due to a leak (Refer to
24 - HEATING & AIR CONDITIONING - STAN-
DARD PROCEDURE).
(6) Install connector boot on switch and repeat
Step 3. If the clutch does not engage, replace the low
pressure clutch cycling switch.
REMOVAL
NOTE: Note: It is not necessary to discharge the
refrigerant system to replace the low pressure
cycling switch.
(1) Disconnect and isolate the battery negative
cable.
(2) Disconnect the connector for the A/C low pres-
sure switch from the top connector on the accumula-
tor.
(3) Unscrew the A/C low pressure switch from the
fitting on the top of the accumulator.
(4) Remove the O-ring seal from the accumulator
and discard.
INSTALLATION
NOTE: Replace the O-ring seal before installing the
low pressure clutch cycling switch
(1) Lubricate the new O-ring seal with clean
refrigerant oil and install it on the accumulator fit-
ting. Use only refrigerant oil of the type recom-
mended for the compressor in the vehicle.
(2) Install and tighten the A/C low pressure switch
onto the accumulator fitting. The switch should be
hand-tightened onto the accumulator fitting.
(3) Reconnect the wiring harness connector to the
A/C low pressure switch.
(4) Reconnect the battery negative cable.
PT
HEATING & AIR COND. - LHD 24 - 19