Air Conditioning System

Griffith 500 System - 1994 pre-Serpentine

Jan 98
I understand that installations vary according to manufacturing date. So the descriptions I am giving are specific to my car ('94 pre-serpentine Griff 500) which was installed post-delivery by the Malaysian factory (car itself was imported from Blackpool). However, the Chimaera's is almost identical. I am no expert on air-con systems and am sharing what I have observed and experienced.

Components of air-con system:

1. Condensor - essentially a heat exchanger like the engine cooling radiator.

2. Compressor - a mechanically driven pump which drives the coolant R134a gas around the a/c cooling circuit.

3. Fan coil - located in fan box to cool air circulated by ventilation system.

4. Reservoir/valve - not sure of correct name, serves to prevent coolant from freezing by regulating flow rate.

5. A/c thermostat.

6. Fuel line cooler.

Electrical circuit description:
A/c thermostat switch provides on/off signals to the compressor and cooling fan relay(s), according to set and measured cabin temperatures. Whenever a/c is switched on the cooling fans are activated, independent of engine temperature. The compressor is engaged if thermostat determines cabin cooling is required. The rotary compressor is driven by power from the engine via a belt, and drive is engaged by an electromagnetic clutch to circulate R134a coolant around a/c cooling circuit.

Coolant circuit description:
R134a coolant is enclosed in its own independent circuit under high pressure connected between components by rubber hoses and seals. From the compressor the gas flows into the condensor, which is placed immediately in front of the radiator separated by a 25cm gap. Radiator and condensor are thermally insulated from each other as far as possible. Gas from the condensor passes through a reservoir/valve which has a small window to observe flow of R134a which is a liquid after cooling. The valve stops flow when there is insufficient flow rate (i.e. if R134a freezes which is catastrophic in this high pressure system). R134a is environmentally friendlier than Freon, but it is still poisonous to humans! From the valve, gas flows through fan coil which provides heat exchange unit to cool cabin. Gas returning to the compressor passes through a fixture attached around the fuel line located near the RHS cam cover.

Mechanical drive:
Drive from flywheel is connected via one belt to the water pump. From the pulleys at the water pump, one belt drives the alternator and the other the a/c compressor.

Important points:
1. R134a fluid has a boiling point of approximately 90C at the system pressure. Therefore, for the a/c system to work, this temperature must not be reached or exceeded. This is not easy within the engine bay where most of the hoses are, especially around the radiator and condensor area unless there is good airflow. Unfortunately, this is not the case when the car is in slow traffic in warm weather, exactly when the a/c is most useful! Therefore, when in slow traffic in summer where engine bay temperatures are often in the 100C range, the effectiveness of the a/c diminishes. Heat soak compounds the problem. Apart from the obvious, it raises the ambient temperature of the fan coil.

2. The cooling of the fuel line makes use of the cooling circuit to prevent fuel from vapourizing before it goes to the injectors. This is known to happen occassionally in warm weather causing engine misfires.

3. The a/c system is fairly unstable in the Griff/Chimaera. A slight loss of pressure in the coolant circuit, and the fact that engine compartment temperatures are very near the R134a's boiling point, any slight changes to these parameters would render the a/c system useless. I have experienced this situation particularly often in the climate where I live. Looking for presence of liquid flow in the window of the reservoir valve helps determine what's happenning in the system.
Kenny Heng

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