This article covers the installation of Air Conditioning on the Alfa 33 907 Series.

All parts come from a wrecked Alfa 33 907 Series which had a factory installed A/C unit. Finding an donor A/C system had begun some years ago but i was reluctanct to trust the hands of mechanics who would install air conditioning to my car. I had been afraid of low quality job and I wouldn't risk letting anyone molest my stock setup car. So, the magic moment of finding a wrecked 33 with A/C installed came and the price to obtain the items was as low as 60 € for compressor, piping, evaporator excluding condensers which had been not worth dealing since the car had suffered from a front end collision. I knew that I wasn't buying something right out of the box, there would surely be problems underlying but since the price of acquiring the parts was just 60 €, I would be able to repair the system according to specs and procedures all within a wide time frame.

Let's make a brief overview of the Alfa 33 A/C system There is so much saying about that system meaning being inefficient, awkward etc. but one can make the system perform in the best way possible. We need to take into account that it is an 80s design with many limitations.

The main components of the AC system are demonstrated on the diagram. 

An A/C system has the primary role to cool down and dehumidify the air inside the passenger compartment. This process requires the items you see in the picture above and the presence of a special gas called refrigerant. This gas (commonly known as Freon) and its variants is widely used in refrigerators and it absorbs heat in order to change its status (liquid to gas and vice versa) which results in conditioned air inside the passenger compartment.

Freon originally used in the Alfa 33 A/C system is CFC - 12 (R12). However since current legislation has prohibited R-12 as of 1996, a new substitute HFC-134a (R134a) is used which more or less produces the same cooling results.

Freon is a non poisonous, non flammable, non explosive and anticorrosive element which suits automotive needs and safety features.

A few words for the A/C system cycle:

Freon leaves the compressor (from port Discharge or "D") in gas form at high pressure (10-18 bar) and temperature (80-100 C) where it enters the condensers. With the help of electric fans and dynamic air, Freon cools down at 40-50C and leaves in liquid form entering the drier filter. The main purpose of this filter is to filter out any moisture present in Freon so that upon entering the expansion valve no freezing or clogging can occur which will reduce the system efficiency and operation. The main role of the Thermal Expansion Valve (TXV) is to atomize Freon which lowers its pressure and temperature; once atomized Freon has entered the evaporator in liquid form, it absorbs heat from the passenger compartment as it needs to change its status (from liquid to gas). In this stage air inside the passenger compartment is significantly cooled down and dehumidified; moisture condensed is drained off the vehicle and Freon returns to the compressor (from port Suction or "S") in gas form and low pressure status. The cycle is then repeated.

As a safety measure, a Trinary Pressure Valve located at the drier filter, serves to

1. Deactivate the compressor electromagnetic coupling in the case of fall or rise in the pressure (serves as a minimum or peak  pressure switch)
2. Activates the right side condenser fan when pressure on the drier filter reaches 15-17 bar (fan operation stops when pressure is reduced by 3-4 bars); left side condenser fan is always activated during the operation of the A/C system
3. Finally a special device ensures fast idle when compressor is engaged.

A few words regarding retrofitting R134a in a R12 A/C system. Some components of the system must be replaced with R134a compatible elements.

1. Recover R12 Freon from the system.Drain off compressor oil. Since R12 is only compatible with mineral compressor oil, ester refrigerant oil must be used with R134a. Simply drain off mineral oil and add the same quantity of ester oil
2. Replace dryer filter specific to R134a desiccant (XH-7 or XH-9)
3. Replace expansion valve specific to R134a
4. Replace O-rings specific to R134a (HNBR type)
5. Fit compressor High and Low pressure service port fittings specific for R134a