Aircon

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E30s are cool. But they won't keep you cool, and if you've got a tin-top in Diamond Metallic Black, then come those summer months you're really going to want something to lower the temperature in the cabin. That's where Aircon comes in.

Aircon.jpg

Overview

Air-conditioning was fitted as an optional extra to all E30s as early as 1984, except the 333i where owners had to choose between aircon and power steering. The system remained largely the same throughout the E30 production run, and is based around a sealed refrigerant oil, just like your fridge at home. I won't explain the science, but as the refrigerant is converted from a gas to a liquid it gains heat; as it goes back to a gas it loses heat and cools, and it is this cooling effect we make use of. It's therefore essential that our system be completely sealed, to keep the refrigerant inside and doing what it should.

The system uses a number of components to compress, liquify, filter and evaporate the refrigerant. Valves regulate the flow of refrigerant through the pipework, and the whole system is controlled from a switch on the dashboard. A pressure switch monitors the condition of the coolant and determines whether or not the compressor needs to be engaged; if required, the clutch locks to drive the compressor.

Since its introduction, the original refrigerant has been made illegal for environmental reasons in the EU and many other states. A conversion kit to a more modern coolant is available from BMW.

The aircon installation is essentially the same across the E30 range. However, different compressor-mounting brackets and pipework lengths mean that kits are not completely interchangeable between models.

Components

Compressor

AirconCompressor.jpg

The compressor is the main pump of the aircon system. Driven by a belt from the same pulley as the alternator and power steering pump, it is mounted on the exhaust side of the block.

The compressor itself does not pump continuously. Instead, it is activated based on the internal pressure of the system and whether or not the Aircon is turned on. That way, the compressor does not sap precious power, and therefore fuel, from the engine when it's not wanted.

Since the refrigerant is constantly changing between a gas and a liquid throughout the system, by the time it meets the compressor it is in a gaseous form. The compressor, unsurprisingly, compresses this gas which makes it hot, before pumping it on to the condenser.

Aircon Clutch

Condenser

AirconCondenser.jpg

The condenser looks suspiciously like a radiator, and is mounted in front of the main vehicle radiator. Its job is to receive the hot and pumped refrigerant gas, and to condense it into a liquid. Its location means that it will receive airflow through the front grille, but it is assisted by an electric fan mounted in front.

The condenser's location and construction make it one of the most fragile elements of the installation. Not only can it be damaged by road debris, but it is also exposed to road spray at its base, leading to rust. This makes them the prime source of refrigerant leaks and therefore total system failure.

Fan

Since the condenser mounts in front of the existing radiator, an electric fan is added to the condenser to aid air flow through the engine bay. The fan bolts directly to the condenser.

Evaporator

Heater matrix containing evaporator

The evaporator is a form of radiator, only in reverse. In the evaporator, the incoming liquid has space to expand into a gas, and as it does so it cools from the inside, creating the lovely chill that we expect from aircon.

The evaporator panel is housed inside the the heater matrix, which is an aircon-specific unit. For that reason, installing the evaporator means changing the entire heater matrix.

Expansion Valve

AirconValve.jpg

The expansion valve directly connects to the evaporator, and regulates the flow of refrigerant.

Pipework

AirconPipework.jpg

The piework of the Aircon system delivers the refrigerant back and forth between the condenser and the evaporator, and everything in between. It follows a snaking path along the right side of the engine bay, entering the cabin area through a pre-stamped hole by the battery tray, and returning through holes drilled into the bulkhead.

The pipes are metal-cored with screw fittings to obtain the best possible seal for the refrigerant. Because of this, they are prone to corrosion over long periods of time, especially if the system is left discharged or if the receiver drier has not been replaced regularly. THey should only be replaced with new genuine BMW components.

Receiver Drier

The Receiver drier is a form of filter, used to remove any moisture from the system that might otherwise corrode the pipework. It processes the liquid refrigerant between the condenser and the evaporator.

Because the receiver drier is so sensitive to moisture, they cannot be exposed to air for any longer than 24hours before being rendered useless. Because of this, the receiver drier is the most commonly replaced component, especially of second-hand aircon systems. It also forms an essential part of the R-134a Kit.

Pressure Switch

Mounted into the receiver drier will be one or two pressure switches, depending on which refrigerant is used. For early R12 systems, two switches detect the high and low pressure of the system. If the pressure is too low, usually caused by a lack of coolant, then the switch prevent the compressor from charging the system. If the pressure is too high, the compressor is again shut off to reduce the pressure. In the R-134a systems, these two switches are combined.

Refrigerant

The system takes 975g (2.1lbs) of refrigerant.

The original refrigerant gas for the aircon system was R-12; one of the more aggressive CFCs. It was banned in 1994.

However, since the E30 was still being produced in some markets in 1994, the final volume of aircon-equiped vehicles received a conversion kit to the less malevolent R-134a. Since the refrigerant in all E30s will be due for replacement (known as "recharging" the system), it is essential to convert your aircon over to an R-134a compatible system.

R-134a Kit

The R-134a kit, available from BMW, includes a new receiver drier, valves, pressure switch and some O-rings, like so:

AirconR134aKit.jpg

Since the kit combines the two pressure switches of the old system into one new unit, the wiring has to be customised to join the signals together. You need to short out the wiring for one of the old switches and solder the new plug supplied in the kit to the wires for the other old switch, connect the new plug to the new switch.

Ancilliaries

Alongside the primary Aircon components, there are other parts that work in conjunction with the aircon to make the car work better.

Radiator

Because of the location of the condenser, the existing radiator is normally a modified unit. Aircon-specific radiators have a different profile, making them deeper as well as taller to provide a larger cooling area. Their height means that their bottom protrudes further down into the valance.

Aircon radiators will also feature a boss (or bolt hole) for the fitting of an extra coolant temperature sensor. This allows the aircon to monitor the temperature of the radiator and increase the speed of the aircon fan if necessary, to prevent overheating.

Two sizes of radiator were available, and are known as UK and Tropical radiators. While not essential to the running of aircon, it is recommended to fit a tropical radiator to minimise the risk of overheating. However, it is possible to install aircon and keep your existing radiator, as long as it has the boss for the temperature sensor.

Valance

To help with the overall cooling of the radiator and condenser, special aircon-specific front valances were fitted to cars with factory-installed aircon. These valances feature an extra cutout (with no blanking plate or grille) to allow more air to flow over the bottom of the radiator.

If you are retrofitting aircon it is not essential to install the aircon-specific valance, but you must ensure that your radiator, condenser and fan are in good condition.

Installation

Main article: Retrofitting Aircon.

Almost every car these days leaves the factory with air-conditioning, and this causes a shock to our soft, pampered bodies when we get into an E30. So to give yourself a (not-so) modern convenience, learn more about retrofitting Aircon.

Common Problems

Aircon systems use a controlled substance at their core. We do NOT recommend working on these systems yourself. In the event of any problems with your aircon system, consult a refrigeration specialist.

Aircon Won't Turn On

You press the switch, it lights up, but nothing happens. Most of the time, this is caused by a lack of refrigerant. If you haven't had the system serviced in a long time, it's not surprising for the cooling gas to have boiled or leaked away. If you don't replace the refrigerator drier then moisture in the system allows the pipes to corrode, leading to leaks. With all the refrigerant gone, there's nothing to provide any cooling effect, so you need to take the car to a professional.