Heater Circuit; Air Conditioning - Basic Principles; Closed Circuit - Lotus Evora Service Notes

Lotus Service Notes
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.
Section PN
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