1. Climate Control Systems Service Air Conditioning System Service
Topics covered in this presentation:
Gauge set and refrigerant
Service ports and valves
Discharging, evacuating and recharging

2. Introduction
The warm/hot part of the air conditioning system contains high pressure refrigerant, and the cool/cold part of the system contains low pressure refrigerant.
Hot
Various faults may occur (for example, clogged compressor or accumulator, leaking evaporator or condenser, blocked orifice tube etc.) that result in system pressures becoming too high or too low.
Hot
Warm
Cold
Cool
Incorrect system pressures can result in inadequate cooling and incorrect operation.
Pressure tests can be performed to help deduce these faults.

3. Gauge Set - 1
The gauge set, normally part of the charging station, is used to measure air conditioning system pressures.
Low Side Gauge
High Side Gauge
Manifold
The gauge set typically consists of the following:
Manifold - This is the main housing onto which the components are connected. It also contains passages to allow refrigerant flow.
High Side Valve
Low Side Valve
High Pressure Hose
Pressure Gauges - One measures high system pressures and the other measures low pressures.
Low Pressure Hose
Service
Hoses
Continued ...

4. Gauge Set - 2
Valves - One for high pressure side, other for low pressure side. When open, valve connects pressure hose to service hose.
Low Side Gauge
High Side Gauge
Manifold
High Pressure Hose -
This is connected to the high pressure service valve.
Low Pressure Hose - This is connected to the low pressure service valve.
High Side Valve
Low Side Valve
High Pressure Hose
Service Hoses - Sometimes only one. They connect to either a charging station (recovery unit) or oil supply tank.
Low Pressure Hose
Service
Hoses

5. Gauge Dials Low Pressure Gauge
The low pressure gauge measures both pressure and vacuum.
Pressure is measured in bar and vacuum is measured in millimetres of mercury (mm-Hg).
The gauge may also have scales to convert pressure and vacuum readings into equivalent evaporator temperatures.
Low Pressure Gauge
High Pressure Gauge
The high pressure gauge measures pressure only.
Pressure is again measured in bar, and the gauge may also convert pressure readings into equivalent condenser temperatures.
High Pressure Gauge

6. Manifold Flow Control - 1
Both Valves Closed
Both the low and high side valves are closed in order to pressure check the system.
There is no refrigerant flow connection between the service valve and the low and high pressure hoses.
The pressure gauges are open to their respective pressure hoses at all times.

7. Manifold Flow Control - 2
Low Side Valve Open
When only the low side valve is open, refrigerant flow occurs between the service valve and the service hoses.
The valves are normally set in this state when charging/recharging the system with refrigerant.

8. Manifold Flow Control - 3
High Side Valve Open
When only the high side valve is open, refrigerant flow occurs between the service hoses and the high pressure hose.
For some systems, the valves are set in this state when starting the charging/ recharging process.

9. Manifold Flow Control - 4
Both Valves Open
When both the high side and low side valves are open, refrigerant is able to flow between the service hose and the high and low pressure hoses.
The valves are normally set in this state when evacuating refrigerant and water/moisture from the system.

10. Refrigerant Types - 1
Two types of refrigerant are typically used in automotive air conditioning systems: R-12 & R-134a.
R-12
R-12 was the most widely used refrigerant. It is non-flammable, chemically stable at all temperatures, has a low boiling point and is soluble in mineral oils.
It was also inexpensive, however, R-12 is a CFC and as such can contribute to the breakdown of the ozone layer if exposed to the atmosphere, so has now been banned in newly produced vehicles. It is, however, still found in older vehicles.
R-12 is normally kept in a white container, and its connections are male with imperial (inch) threads.

11. Refrigerant Types - 2 R-134a
R-134a has replaced R-12 as the most commonly used refrigerant in automotive systems. R-134a is an HFC and does not contain the ozone depleting chlorine atoms that have made R-12 obsolete.
R-134a is non-flammable, chemically stable at all temperatures and has a low boiling point (but slightly higher than R-12). However, its operating pressures are higher than those of R-12.
R-134a is normally kept in a light blue container, and its connections are female with metric (millimeter) threads.

12. R-12 Service Port
The R-12 service fittings that connect to the charging station hoses have male imperial threads. There are normally two, one for the low pressure side and one for the high pressure side. The connections are of different sizes so they cannot be incorrectly fitted.
Male thread fitting
To charging station
The service fittings contain Schrader valves, which behave in the same way as a tyre air valve, only allowing refrigerant flow when depressed. Therefore, the charging station hose incorporates a depressor to activate the Schrader valve.
Schrader valve
To system
The service fittings are normally situated in an accessible position to allow easy connection and disconnection.
It is important that a dust cap is fitted over the Schrader valve when the service port is not in use to prevent dirt contamination.

13. R-134a Service Port
The R-134a service fittings that connect to the charging station hoses are a Quick Disconnect type (QD). There are normally two, one for the low pressure side and one for the high pressure side. The connections are of different sizes so they cannot be incorrectly fitted.
The large difference in the service fittings between R-12 (screw) and R-134a (QD), ensures that the wrong type of charging station, with the wrong refrigerant, cannot be used.
To system
QD Fitting
To charging station
The R-134a service ports also use Schrader valves and have the connections situated in accessible positions.
Schrader valve
As before, a dust cap must be over the Schrader valve when the service port is not in use.

14. Inspection Sight Glass
Inspection sight glasses are typically found in the accumulator (drier) or in the system hose line.
Sight glass
They are used to visually inspect the state of the refrigerant in the system.
Inspection sight glasses may also be used to observe the operation of the air conditioning system during clutch cycling, when a stream of bubbles appears.
Note: Inspection sight glasses are not normally used in R-134a systems as the sight glass appears cloudy, which could lead to misinterpreted results.
Accumulator

15. Typical Sight Glass Observations
Clear - Typically indicates a full system, but can also indicate an almost empty or overfull system.
Cloudy
Cloudy - This may indicate that the desiccant bag in the accumulator, or drier, has broken down and its contents are moving round the system.
Bubbles - Indicates that moisture is in the system. However, bubbles during clutch cycling or start-up is normal.
Bubbles
(Foamy)
Foamy - Indicates that the refrigerant level is low.
Oil
Streaked
Oil Streaked - Indicates that the refrigerant level is low, allowing compressor oil to move through the system.

16. Discharging the System
High pressure valve open
The air conditioning system needs to be discharged (recovered) whenever the system needs to be opened, or a component needs to be replaced.
Low pressure
valve open
A charging station is used to remove the refrigerant from the system.
The charging station is connected directly to the low and high pressure service valves, both pressure valves open.
Refrigerant
recovery
The recovered refrigerant is filtered and collected for reuse. Oil is also drained and the amount must be noted for refilling the system, once repairs/ replacements have been performed.
The refrigerant recovery is normally controlled by the charging station.
Charging station

17. Evacuating the System
High pressure valve open
An air conditioning system needs to be evacuated of all gas and moisture whenever it has been discharged, or opened to the atmosphere.
Low pressure
valve open
Both the high and low pressure valves are normally opened in order to evacuate the system.
A vacuum pump within the charging station is connected to the system. A vacuum is then created within the system and air (vapour) removed from the system.
The vacuum created causes any moisture in the system to boil at room temperature.
Leaks can be detected by checking the vacuum over a period of time.
Charging station

18. Recharging the System
High pressure valve closed
This process charges the system with the correct amount of refrigerant and oil by using the charging station.
Low pressure
valve open
The amount of refrigerant to be added is measured by weight, pounds or grams, and is normally found on an A/C label under the bonnet.
Typically, the high pressure valve is closed and the low pressure valve is opened during this process.
Before charging with refrigerant, the correct type and amount of oil must be added. The vacuum left within the system when evacuating draws the refrigerant into system.
After charging, the system pressures must be checked.
Charging station

19. Possible Recharging Errors
Undercharge
Undercharge occurs when not enough refrigerant has been charged into the air conditioning system. It can cause inadequate cooling at high heat loads, cause the refrigeration cycle to occur faster than normal and reduce the system pressures.
Overcharge
Overcharge occurs when too much refrigerant has been charged into the system.
With overcharge, there is little or no room to create vapours, so only liquid will be pumped round the system causing inadequate cooling. The system pressures will be much higher than normal and the compressor may run constantly.
Water/Moisture
Water/moisture in the system can cause acidic corrosion when the refrigerant and water mix. The water can also freeze, causing erratic system operation and not allowing system pressures to be measured correctly.