Lotus Elise Service Notes page 458

Lotus Service Notes Section XA
PH.4 - A C. CLUTCH & COOLING FAN CONTROL
A.C. Control
When the a.c. request button on the fascia is pressed, the signal is routed through the evaporator thermo-
static switch (to ensure no icing) and the trinary switch (to check acceptable refrigerant pressure) before feed-
ing the ECM input. Before energising the compressor clutch, the ECM first adjusts the idle air control valve to
compensate for the increased engine load. Compressor switching will be inhibited under certain conditions,
including: engine cranking; wide open throttle; excessive coolant temperature.
Cooling Fan Control - Elise
Elise models with a.c. are fitted with two radiator fans, one switched by the engine ECM on the basis of
coolant temperature (as for non-a.c. cars), with the second fan switched via the a.c. request push switch.
Cooling Fan Control - Exige
Exige models with a.c. are fitted with two radiator fans controlled by the engine ECM and a relay module
(mounted in the front services compartment), and operate always as a pair, either;
- off;
switched in series for half speed operation;
switched in parallel for full speed operation.
Under normal conditions, the fans operate only at vehicle speeds below 25 mph (40 km/h). When coolant
temperature reaches approx. 102°C, the fans operate at half speed, with full speed operation switching in if
coolant should reach 108°C. When the trinary switch on the receiver-drier indicates that a.c. is operating and
that condenser cooling is required, the fans will operate at fast speed regardless of coolant temperature.
Engine Malfunction
If the engine ECM detects certain types of engine malfunction, including misfire, or anomolies in coolant
temperature or intake air temperature, the cooling fans will be switched to full speed as an engine protection
strategy.
PH.5 - COOLANT RE-CIRCULATION PUMP
In order to control engine temperature in conditions of heat soak after engine switch off, a.c. cars are
equipped with an electric pump to circulate coolant through the engine and prevent localised boiling. The
pump is mounted at the rear of the cylinder head in the radiator by-pass circuit and when operating, pumps
coolant from the engine outlet elbow back into the engine at the thermostat housing. A smaller flow will also
occur through the radiator and heater circuits.
Pump Control
Elise: The re-circ. pump will operate with ignition off, when coolant temperature as sensed by a thermal switch
in the radiator feed pipe at the bottom front of the engine bay, is above approx. 100°C. A relay/timer module
mounted in the front services compartment, limits the operating time to 20 minutes.
Exige: The re-circ. pump is controlled by the engine management ECM and will operate the pump, with ignition
off, at temperatures over 105°C (off at 100°C) as indicated by the engine coolant temperature sensor. A timer
function limits pump operation time to 20 minutes.
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