A/C COMPRESSOR CLUTCH CONTROL
The A/C compressor electromagnetic clutch is powered by the
A/C relay. Compressor operation requires that the A/C relay be
activated by both Electronic Climate Control (ECC) module and Engine
Control Module (ECM). The ECM turns A/C compressor off when engine is
at full acceleration, at high engine temperature, and for 5-10 seconds
after starting engine.
The ECC control module normally supplies voltage to A/C
relay, except when heater (blower motor) fan is off and vehicle speed
is less than 20 MPH, when heater fan is off and recirculation is on,
or momentarily when under full acceleration.
If A/C is switched off using the AC OFF switch, ECC control
module will cut supply voltage to relay, turning off compressor.
However, this does not apply when air distribution control is in
defrost setting, since A/C is always on in this case.
A/C PRESSURE SWITCHES
The A/C compressor is connected in series with the lowpressure
switch, high-pressure switch, and safety switch. The highpressure
and safety switch cut power to the A/C compressor if pressure
in the A/C high-pressure circuit becomes excessive, supplying a signal
to ECM to start cooling fan.
The low-pressure switch (pressostat) turns A/C compressor on
and off to maintain pressure within limits.
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1995 854T and 1998 V70R