Lotus Elise S1 Service Notes page 450

Lotus Service Notes Section PH
Condenser
The aluminium condenser is horizontally mounted beneath the engine cooling radiator, and is of parallel
flow construction. The hot vapour received by the condenser from the compresser, releases heat to the
surrounding air via the condenser finning, with airflow boosted by two electric fans mounted below the con-
denser, and ram air flow caused by vehicle movement.
Receiver-Drier
The receiver-drier unit, mounted on the right hand side of the radiator duct, houses a screen sack filled
with desiccant to absorb traces of moisture and other contaminants from the refrigerant. A sight glass built into
the top of the receiver-drier enables a quick check of the refrigerant charge in the system. If the refrigerant
charge is low, a stream of bubbles will be visible at the sight glass. Note: A clear sight glass, may indicate that
the system is correctly charged, or completely empty, although the latter situation is usually accompanied by
oil streaks.
A trinary switch on the receiver-drier senses the pressure of refrigerant and allows system operation only
within a pressure range of 2 to 32 bar in order to prevent damage from too high a pressure, or from compressor
oil starvation caused by too low a pressure. A third switching point, at 17.5 bar, is used on Exige models for
condenser fan control input to the engine ECM (see sub-section PH.4). An additional safeguard is provided in
the form of a high pressure relief valve in the condenser inlet pipe, which opens at 38 - 41 bar.
Expansion Valve
The expansion valve block is fitted into the high and low pressure lines at the evaporator, and provides a
restriction to the flow of high pressure liquid into the evaporator, such that the consequent pressure drop
causes a change of state from a high temperature, high pressure liquid, to a low pressure, low temperature
atomised liquid. The expansion valve senses the pressure of refrigerant leaving the evaporator, and modu-
lates the valve inlet opening in order to provide optimum cooling performance.
Evaporator
The evaporator is a tube and fin type heat exchanger mounted in a plastic housing fitted into the chassis
well ahead of the passenger compartment footwell. All incoming airflow is directed through the evaporator,
before being directed through or around the heater matrix, through the blower fan, and into the air distribution
chamber.
The low pressure liquid refrigerant flowing into the evaporator via the expansion valve, begins to boil
(evaporate) and in so doing, draws the necessary heat for this process from the airstream passing over the
evaporator surface. This airstream is consequently cooled, and is directed through the various outlet vents to
the passenger compartment.
When the a.c. switch is pressed by the driver, and other parameters allow it (i.e. ignition on, blower fan
speed selected, a.c. pressure switch closed), the a.c. circuit is activated and the compressor clutch is engaged.
In order to prevent the possibility of ice formation at the evaporator, a thermostatic switch is housed inside the
evaporator casing, with a temperature sensing capillary line inserted into the outlet side of the finning. The
switch is used to cycle the compressor on and off as necessary to maintain the minimum output air tempera-
ture without danger of icing.
The inlet and outlet pipes connect to the evaporator via the expansion valve block, into which they are
sealed using 'O' rings and a clamp plate. The inlet is supplied from the receiver-drier, and the outlet feeds the
compressor.
Heater System
The heater system uses engine coolant to provide a heat source transferred to the interior airstream via
a heat exchanger matrix mounted in an 'air blend' unit housed within the chassis well, ahead of the cabin
footwell. The coolant is fed from the cylinder head outlet pipe via an alloy pipe running along the outside of the
RH chassis side rail. Coolant is returned via a similar pipe along the LH chassis rail to the engine side of the
thermostat housing.
Air temperature is controlled by an air blend flap within the heater housing which directs a varying propor-
tion of the airflow through, or around the matrix as determined by the position of the temperature selector knob.
When full cold is selected, the control mechanism closes an electrical microswitch which operates a vacuum
solenoid valve, in order to supply a vacuum operated water valve to close the coolant supply to the matrix. The
water valve is fitted at the right hand bottom of the engine bay.
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