Lotus Elise / Lotus Exige. Instruction - part 97

    

Lotus Service Notes                                 Section PL

Page 2

Heater Circuit

Water feed pipe along outside
of RH chassis siderail

Heater
matrix

Water return pipe
along outside of

Water return to

LH chassis siderail

engine side of
thermostat

    

 p77c

Coolant re-circulation pump

Refrigerant Circuit

Receiver-drier

Feed & return pipes
along outside of RH
chassis siderail

Condenser

Expansion valve

        Compressor

Evaporator casing

        p78c

    

Lotus Service Notes                                 Section PL

Page 3

PL.1 - GENERAL DESCRIPTION

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 an outlet on the left hand side of the cylinder head, and via an alloy pipe
running along the outside of the RH chassis side rail to the matrix.  Coolant is returned via a similar pipe along
the outside of the LH chassis rail to a by-pass return pipe on the left hand side of the engine.

Air temperature is controlled by a pair of air blend flaps within the heater housing which direct a varying

proportion of the airflow through, or around the matrix as determined by the position of the temperature selec-
tor knob.  Note that no water valve is fitted, such that the matrix is always 'hot' when the engine is running.

Air Conditioning (If fitted) - Basic Principles

The air conditioning unit uses a cycling clutch system with a thermostatic expansion valve to provide

refrigerated air to the vehicle interior.  The system comprises:
-

a closed circuit containing refrigerant R134a;

-

a compressor mounted on the front side of the engine, driven by multi-vee belt from the front end of the
crankshaft via an electromagnetic clutch;

-

a condenser mounted horizontally at the front of the car, beneath the engine cooling radiator;

-

an evaporator unit (cooler) fitted in the chassis well ahead of the cabin footwell;

-

a thermostatic expansion valve fitted at the inlet connection to the evaporator;

-

a receiver-drier unit mounted above the heater/a.c. unit

Closed Circuit

The closed refrigerant circuit should not be opened unless absolutely necessary, and only then using

appropriate refrigerant recovery equipment.  Never allow the refrigerant to vent to atmosphere.  Refer to sub-
section PL.5.  Failure to observe these precautions may result in personal injury.

Expansion

Trinary switch

valve

Service ports

Condenser

Compressor
connections

Receiver-drier

High pressure
relief valve

Sill pipes

        p75c

    

Lotus Service Notes                                 Section PL

Page 4

Compressor

When the engine is running, and the refrigeration controls demand it, the electromagnetic clutch incorpo-

rated in the compressor pulley is energised, which then locks the pulley to the shaft and drives the compressor.
The rotary vane type compressor operates to discharge refrigerant vapour at high pressure and temperature
into the condenser.  The compressor is lubricated by a quantity of special refrigerant oil, most of which is
retained in the compressor, with the remainder being circulated with the refrigerant.  An integral thermal cut-out
switch is designed to prevent overheating damage by interrupting the compressor clutch circuit if an exces-
sively high temperature is detected.

A thermostat, sensing the temperature of the refrigerated air as it leaves the evaporator, signals the

compressor to cycle on and off.  In order to avoid engine stalling and to maintain idle speed when the compres-
sor driving load is placed on the engine, the a.c. request and compressor command signals are processed by
the engine management ECU, which amends the idle air control valve position as necessary.

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 compressor, 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.

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 past the heater matrix, and then 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 through the
evaporator.  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.
A thermostat, using a sensor inserted into the outlet side of the evaporator finning, monitors the temperature of
the refrigerated air and signals the compressor to cycle on and off in order to maintain outlet air temperature
just above freezing.

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.

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.

By sensing the temperature and pressure of refrigerant leaving the evaporator, the expansion valve is

able to modulate the flow of refrigerant into the unit to optimise the cooling performance.

Receiver-Drier

 The receiver-drier unit is fitted into the refrigerant line between the condenser and evaporator expansion

valve, and houses a screen sack filled with desiccant to absorb traces of moisture and other contaminants from
the refrigerant.  The unit is mounted in the chassis well above the heater/a.c. unit.  A sight glass built into the
top of the receiver-drier allows a visual assessment of refrigerant charge to be made - 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.  If refrigerant charge is low, a stream of bubbles will be visible at the sight glass.

A trinary switch fitted into the top of 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 system damage from too high
a pressure, or from compressor oil starvation damage caused by too low a pressure.  A third switching point is
used to engage the two condenser fans at half speed at pressures over 17.5 bar (see also sub-section KH.5).
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.

    

Lotus Service Notes                                 Section PL

Page 5

PL.2 - HEATER/A.C. AIRFLOW OVERVIEW

The major units of the Heating Ventilation and Air Conditioning (HVAC) system comprise a dual intake

blower fan, an evaporator housing (with no evaporator fitted for non a.c. cars), a heater housing and an airflow
distribution unit.  The fan blower unit and the combined evaporator/heater unit are mounted in the chassis
climate chamber ahead of the cabin footwells, with the airflow distribution unit mounted on the top of the
chassis scuttle area.  Ambient air is collected from the radiator air intake duct via two ports in the radiator
ducting, which mate to apertures in the chassis front crossmember.  Moulded ducting on the rear side of the
chassis front face directs this air, via a shut off butterfly flap valve on a.c. cars (to provide a recirc. function), to
the blower fan front intake.  The rear intake of the double sided fan housing is connected to perforated ports in
the front wall of each footwell.

The fan blower unit directs all airflow through the a.c. evaporator (if fitted), after which a pair of linked air

blender flaps, control the proportion of air which flows through the heater matrix.  The upper flap is driven by a
stepper motor from the cockpit temperature selector, with the lower flap linked to the upper by toothed belt.
After leaving the HVAC chamber, air is ducted to a distribution chamber mounted on the top of the chassis
scuttle which distributes air to screen, face level vents and footwell vents.  The distribution chamber contains
a horizontal, three vane, rotary flap, driven by a stepper motor, and controlling outlets to the screen and face
level vents.  A link rod connects this flap to a second flap controlling airflow to the footwells.  Ducting for the
windscreen vents is incorporated into the underside of the fascia top panel.

Schematic Airflow

Face level
vent

Windscreen
vent

Footwell vent

Re-circ. ports in
footwell

Blower fan

Heater matrix

A.C. evaporator

Stepper motor for

Re-circuation flap

re-circ. flap

(a.c. cars only)

Chassis front wall

Crash structure

Fresh air in

        p101