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Lotus Evora. Instruction - part 80

Lotus Service Notes

Section PN

Refrigerant Circuit

Expansion valve

High pressure

vapour line

Receiver-

drier

Condenser Evaporator

Low pressure

vapour line

Compressor

p115

Heater Circuit

Heater matrix

Heater

Thermostat return rail

housing

Header

Coolant outlet tank

housing

Air bleed

screws

Outlet

from head

Re-circulation pump

Pipe runs

through LH sill

p116

Lotus Service Notes

Section PN

PN.1 - GENERAL DESCRIPTION

The heating, ventilation and air conditioning (HVAC) main unit comprises a plastic casing secured to the

front face of the main chassis tub, housing the fan blower, a.c. evaporator and heater matrix, with a fresh air

inlet adaptor on its top face, a re-circulation intake port on the rear face, and an outlet to the air distribution

chamber on the top rear of the unit.

Heater Circuit

The heating system uses engine coolant to provide a heat source transferred to the interior airstream via

a heat exchanger matrix mounted within the HVAC unit. Hot coolant is directed from an offtake on the engine

outlet housing at the rear of the cylinder head, via a re-circulation pump (see below), into pipework running

through the LH sill, and connecting to the heater matrix. The outlet from the matrix connects to return pipwork

routed alongside the supply line to the LH end of the heater return rail. This rail runs down the 'V' of the cylin-

der block, alongside the by-pass pipe, and connects to the engine side of the thermostat housing at the front

of the engine.

In conditions of 'heat soak', after stopping a hot engine, the electric re-circulation pump mounted in the

heater supply line at the LH side of the engine bay, is energised under engine ECU control, to pump coolant

around the heater circuit and limit the potential for localised boiling within the cylinder head.

Air Conditioning - Basic Principles

The air conditioning unit uses a variable displacement compressor system with a thermostatic expansion

valve to provide refrigerated air to the vehicle interior. The system comprises:

a closed circuit containing refrigerant R134a;

a variable displacement 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 fixed to the front of the engine cooling radiator, between the front subframe longerons and

tilted forwards at 45°;

an evaporator unit (cooler) contained within the HVAC housing ahead of the cabin footwell bulkhead;

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

a refrigerant receiver-drier unit mounted on the outside of the front subframe RH longeron, ahead of the

RH front wheel.

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 PN.5. Failure to observe these precautions may result in personal injury.

The discharge hose from the engine driven compressor connects to a rigid aluminium pipe at the RH

side of the engine bay, with the junction supported on an vibration isolator plate. The high pressure discharge

pipe is routed through the RH body sill via foam support blocks clamped to the outside of the chassis main

siderail. At the rear of the RHF wheelarch, the pipe rises to another junction plate secured to the outside of

the subframe longeron, where it connects to the condenser supply pipe/hose assembly which runs over the

wheelarch area to the RH side of the condenser, to which it connects on the topside. The condenser outlet

union is sited alongside the inlet union, and supplies a rigid aluminium pipe running to the receiver-drier unit

mounted ahead of the RHF wheelarch. From here, another pipe, incorporating the trinary switch, connects to

the expansion valve mounted on the evaporator inlet pipe at the RH side of the HVAC unit. Refrigerant leaving

the evaporator passes through the expansion valve into a pipe/hose assembly which connects to a sill pipe

and then continues to run in parallel to the supply line back to the compressor.

Lotus Service Notes

Section PN

Compressor

The variable displacement compressor is mounted on the front side of the engine, and is driven by the

multi-rib auxiliary belt. The compressor operates to discharge refrigerant vapour at high pressure and tem-

perature into the condenser and 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. The compressor contains a ring of

cylinders with axes parallel to the compressor drive shaft, and whose pistons are driven up and down the bores

by a rotating 'swash plate', the angle of which, in relation to the drive shaft, is variable. With a small swash plate

angle, a short piston stroke is produced for a low refrigerant flow; a high swash plate angle results in greater

piston stroke for a higher flow of refrigerant. The angle of the swashplate is determined by the pressure dif-

ferential between that on top of the pistons, and that within the housing, applying a force to the underside of

the pistons, in conjunction with a coil spring around the drive shaft.

This differential is controlled by a solenoid valve under ECU control, using pulse width modulation. When

the valve is open, the output from the cylinders is bled off to the compressor housing to result in no pressure

differential. The angle of the swashplate is then determined by the coil spring which pushes the plate to a

near neutral position to provide minimal flow. As the valve is progressively closed, the pressure differential

increases, with the pressure on top of the pistons pushing the swashplate to a greater angle, and producing

an increased refrigerant flow.

The engine ECU is programmed to minimise refrigerant flow until an a.c. request is made, thus allowing

the compressor to be run at all times in the interests of system lubrication, and the reduction of inactivity dam-

age.

To safeguard the drive system in the event of compressor seizure, an electromagnetic clutch in the pulley

hub is used to disengage the drive as signalled by a sensor in the compressor nose. The clutch will also be

disengaged by the ECU if a loss of refrigerant is detected by the trinary switch (see below).

Hot refrigerant vapour from the compressor is fed via flexible hoses and alloy pipwork routed through the

body RH sill, to the front mounted condenser.

Condenser

The aluminium condenser is a 'parallel flow' heat exchanger, configured with side mounted collector tanks

interconnected by 40 oval shaped, horizontal tubes, all provided with generous finning. The unit is fixed to the

front of the engine cooling radiator, sited between the longerons of the front subframe, and angled forwards at

45°. The hot vapour received from the compressor, is admitted into the top section of the RH condenser tank,

and flows through 32 tubes to the LH tank before returning to the lower section of the RH tank via the bottom

8 tubes. In so doing, heat is released to the surrounding air via the condenser finning, with airflow boosted by

two electric fans mounted on top of the engine radiator, and ram air flow caused by vehicle movement.

A union at the bottom of the RH tank directs the condensed, liquid refrigerant into pipework connecting

with the receiver-drier.

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 on the outside of the subframe RH longeron, ahead of the RHF wheel.

A trinary switch fitted into the pipe between the receiver-drier and expansion valve supplies a pressure

signal to the engine ECU, which then 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. This data is also used by the ECU to engage the two condenser fans at half speed at

pressures over 17.5 bar (see also sub-section KJ.5).

Expansion Valve

The expansion valve block is fitted into the high and low pressure pipes at the evaporator connection, and

provides a variable restriction to the flow of high pressure liquid into the evaporator, such that the consequent

pressure drop causes a change of state to a low pressure, low temperature atomised liquid.

By sensing the temperature and pressure of refrigerant leaving the evaporator, the expansion acts to

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

Lotus Service Notes

Section PN

Evaporator

The evaporator is a 'serpentine' type heat exchanger mounted within the HVAC unit. 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 across the evaporator finning. 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. system pressurised, ambient temperature above 3°C), the a.c. circuit is activated and re-

frigerant flow established. A thermostat, using a thermistor positioned against the outlet side of the evaporator

finning, monitors the temperature of the refrigerated air and signals the ECU to regulate refrigerant flow in order

to provide an output air temperature just above that at which ice may form on the evaporator.

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 into

pipework routed through the body RH sill, to the compressor.

Ventilation

Air in the cabin is exhausted via an outlet vent at the left hand side of the rear bulkhead, and another at

the bottom right hand corner of the bulkhead. Ducting from each of these vents connects to the rear luggage

compartment, from which air escapes to atmosphere through two one-way flap valves fitted in the rear transom

and concealed by the rear bumper.

PN.2 - HEATER/A.C. AIRFLOW OVERVIEW

The HVAC unit comprises left and right hand plastic mouldings sandwiched together and containing a

pair of blower fans supplied from two intake sources, an a.c. evaporator, a heater matrix, and two electrically

controlled flaps; one for the fresh air intake and one for the heater matrix.

Outlet to screen vents

Outlet to face level vents

Air distribution unit

Outlet adaptor Duct to

passenger

footwell

Pollen filter

Distribution

drum actuator

Intake adaptor

Fan housing

Fixing to chassis

bulkhead

Fixing to subframe Refrigerant connections

crossmember

Temperature flap actuator

Fixing bracket to subframe

p118

Content .. 78 79 80 81 ..