AIR CONDITIONING (A/C) CLUTCH RELAYÐPCM
OUTPUT
The powertrain control module (PCM) activates the
A/C compressor through the A/C clutch relay. The
PCM regulates A/C compressor operation by switch-
ing the ground circuit for the A/C clutch relay on
and off. The relay is located in the Power Distribu-
tion Center (PDC) (Figs. 17 or 18). For the location of
the relay within the PDC, refer to label on PDC
cover.
When the PCM receives a request for A/C from A/C
evaporator switch, it will adjust idle air control (IAC)
motor position. This is done to increase idle speed.
The PCM will then activate the A/C clutch through
the A/C clutch relay. The PCM adjusts idle air con-
trol (IAC) stepper motor position to compensate for
increased engine load from the A/C compressor.
By switching the ground path for the relay on and
off, the PCM is able to cycle the A/C compressor
clutch. This is based on changes in engine operating
conditions. If, during A/C operation, the PCM senses
low idle speeds or a wide open throttle condition, itwill de-energize the relay. This prevents A/C clutch
engagement. The relay will remain de-energized un-
til the idle speed increases or the wide open throttle
condition exceeds 15 seconds or no longer exists. The
PCM will also de-energize the relay if coolant tem-
perature exceeds 125ÉC (257ÉF).
AUTO SHUT DOWN (ASD) RELAYÐPCM OUTPUT
The ASD relay is located in the Power Distribution
Center (PDC) (Figs. 17 or 18). For the location of this
relay within the PDC, refer to label on PDC cover.
The ASD supplies battery voltage to the fuel pump,
fuel injector, ignition coil, generator field winding
and oxygen (O2S) sensor heating element. The
ground circuit for the coil in the ASD relay is con-
trolled by the powertrain control module (PCM). The
PCM operates the relay by switching the ground cir-
cuit on and off.
The fuel pump relay is controlled by the PCM
through same circuit that the ASD relay is con-
trolled.
The powertrain control module (PCM) energizes
the fuel pump through the fuel pump relay. (The
PCM was formerly referred to as the SBEC or engine
controller). Battery voltage is applied to the relay
from the ignition switch. The relay is energized when
a ground is provided by the PCM. The relay is lo-
cated in the Power Distribution Center (PDC) (Figs.
17 or 18). For the location of fuel pump relay within
PDC, refer to label on PDC cover.
For the 1994 model year, the ballast resistor and
ballast resistor bypass relay are no longer used to
control the fuel pump circuit.
DATA LINK CONNECTORÐPCM OUTPUT
Refer to the previous paragraphs on Data Link
ConnectorÐPCM Input for information.
EMR LAMPÐPCM OUTPUT
The EMR lamp is not used for the 1994 model
year.
Fig. 16 Vehicle Speed SensorÐTypical
Fig. 17 PDCÐYJ Models
Fig. 18 PDCÐXJ Models
14 - 24 FUEL SYSTEMJ
AIR CONDITIONING (A/C) CLUTCH RELAYÐPCM
OUTPUT
The powertrain control module (PCM) activates the
A/C compressor through the A/C clutch relay. The
PCM regulates A/C compressor operation by switch-
ing the ground circuit for the A/C clutch relay on
and off. The relay is located in the Power Distribu-
tion Center (PDC) (Figs. 17 or 18). For the location of
the relay within the PDC, refer to label on PDC
cover.
When the PCM receives a request for A/C from A/C
evaporator switch, it will adjust idle air control (IAC)
motor position. This is done to increase idle speed.
The PCM will then activate the A/C clutch through
the A/C clutch relay. The PCM adjusts idle air con-
trol (IAC) stepper motor position to compensate for
increased engine load from the A/C compressor.
By switching the ground path for the relay on and
off, the PCM is able to cycle the A/C compressor
clutch. This is based on changes in engine operating
conditions. If, during A/C operation, the PCM senses
low idle speeds or a wide open throttle condition, itwill de-energize the relay. This prevents A/C clutch
engagement. The relay will remain de-energized un-
til the idle speed increases or the wide open throttle
condition exceeds 15 seconds or no longer exists. The
PCM will also de-energize the relay if coolant tem-
perature exceeds 125ÉC (257ÉF).
AUTO SHUT DOWN (ASD) RELAYÐPCM OUTPUT
The ASD relay is located in the Power Distribution
Center (PDC) (Figs. 17 or 18). For the location of this
relay within the PDC, refer to label on PDC cover.
The ASD supplies battery voltage to the fuel pump,
fuel injector, ignition coil, generator field winding
and oxygen (O2S) sensor heating element. The
ground circuit for the coil in the ASD relay is con-
trolled by the powertrain control module (PCM). The
PCM operates the relay by switching the ground cir-
cuit on and off.
The fuel pump relay is controlled by the PCM
through same circuit that the ASD relay is con-
trolled.
The powertrain control module (PCM) energizes
the fuel pump through the fuel pump relay. (The
PCM was formerly referred to as the SBEC or engine
controller). Battery voltage is applied to the relay
from the ignition switch. The relay is energized when
a ground is provided by the PCM. The relay is lo-
cated in the Power Distribution Center (PDC) (Figs.
17 or 18). For the location of fuel pump relay within
PDC, refer to label on PDC cover.
For the 1994 model year, the ballast resistor and
ballast resistor bypass relay are no longer used to
control the fuel pump circuit.
DATA LINK CONNECTORÐPCM OUTPUT
Refer to the previous paragraphs on Data Link
ConnectorÐPCM Input for information.
EMR LAMPÐPCM OUTPUT
The EMR lamp is not used for the 1994 model
year.
Fig. 16 Vehicle Speed SensorÐTypical
Fig. 17 PDCÐYJ Models
Fig. 18 PDCÐXJ Models
14 - 24 FUEL SYSTEMJ
