Please note that this article was developed using an IRCM from an 87/88 Turbocoupe.
IRCM's from other years may or may not have any resemblance to the one used for the article.
The primary function of the IRCM in our Turbo Coupes is to provide a controlled source
of power (switched 12 volts) to the engine control computer (ECC) and it's related components.
Additionally, it has several secondary functions; it houses and controls the fuel pump relay and
the engine cooling fan relay(s), and also controls the air conditioning clutch by means of a
solid-state transistorized switching circuit.
ECC power relay
When 12 volts from the ignition switch is applied to the IRCM, the ECC relay is energized
and supplies power for the internal IRCM circuitry and the ECC itself. Note that this power
source is switched via the ignition, and is not constantly present.
Fuel pump relay
Once the ECC power relay applies power to the ECC, a signal is sent by the ECC to the IRCM
that energizes the fuel pump relay, which in turn supplies power to the fuel pump. Note that
this circuit has other protective devices, e.g. the inertia switch in the trunk that shuts
off power to the the fuel pump in case of a collision.
Cooling fan relay(s)
As measured by the ECT sensor, when the coolant temperature reaches 210° the ECC signals
the IRCM to turn on the primary (passenger side) radiator cooling fan. Once the temperature
drops below about 190°, the fan is shut off. If the temperature exceeds about 220° ,
the ECC also tells the IRCM to turn on the secondary (drivers side) cooling fan. The shut-off
temperature for this fan is around 200°. Additionally, when the air conditioning
compressor is turned on, the ECC will cause the IRCM to energize the primary fan. Finally,
if the A/C high-side pressure exceeds about 310psi, the secondary fan will be energized.
Air conditioning clutch control
The air conditioning compressor clutch is powered through a solid-state transistor circuit
in the IRCM. Basically if the A/C is active, the circuit is told to energize the clutch. This changes
somewhat in the case of a vehicle with electronic climate control. Additionally this circuit
is controlled by the A/C low pressure switch which disallows the A/C clutch being energized
if the refrigerant pressure is too low.