Air conditioning control system

5. Evaporator Trinary pressure switch This switch, located in the high pressure line between

As this change of state occurs, a large amount of the receiver drier and the expansion valve, monitors latent heat is absorbed. The evaporator is therefore refrigerant pressure and by means of the relay cooled and as a result heat is extracted from the air controls the following system functions: flowing across the evaporator. The air flow is controlled by the blower fans which can be operated at various speeds.

To prevent liquid passing through to the compressor, a capillary tube (6), attached to the outlet pipe of the evaporator (5) and connected to the thermostatic expansion valve (4), controls the amount that the valve opens and closes in relation to the temperature of the low pressure high temperature refrigerant vapour (F4) at the outlet. The atomised refrigerant then passes through the evaporator (5). Fan blown air (A2) passes through the matrix (A3) of the evaporator and is cooled by absorption due to the low temperature refrigerant passing through the Condenser cooling fan evaporator. The condenser cooling fan operates automatically whenever the air conditioning system is switched on. A thermostat is positioned in the airflow leaving the evaporator to sense the temperature of the exterior fins. Should ice begin to form, due to a too cold condition, it will signal to disengage the electro-mechanical clutch on the compressor (1).

From the evaporator, low pressure, slightly superheated refrigerant (F5) passes to the compressor to complete the cycle.

AIR CONDITIONING CONTROL SYSTEM

The air conditioning control system comprises relays, thermostat, pressure switches, and a control panel.

1. Blower control

Together these controls, in conjunction with the

The blower can be operated at various speeds by

cooling fan, compressor clutch and blower, enable

turning the blower switch to the required position.

minimal input to maintain the required environment

When the blower is switched off, the air conditioning

inside the vehicle.

system will not operate. Selecting air conditioning provides the added facility of

2. Temperature control

cooled air available to be mixed with warm air from

Rotate the temperature control switch clockwise to

the heater system to give the required interior

increase the cooling effect. Use in conjuction with the

environmental conditions.

blower control as required.

1. Refrigerant pressure drops below 2.0 bar, 29₂ lbf/in (due to possible leakage), the compressor’s electro-mechanical clutch is dis-engaged.₂
2. When pressure rises above 2.0 bar, 29 lbf/in the compressor’s clutch is re-engaged.
3. Refrigerant pressure rises above 32 bar, 455₂ lbf/in (due to possible blockage), even with cooling fan operation, the compressor’s electro-mechanical clutch is dis-engaged. When the pressure drops below 26 bar, 375₂ lbf/in the compressor clutch is re-engaged.