Mazda Training manual — part 275

Air Conditioning Fundamentals

TC070-05-01S

10 – SERVICING AIR
CONDITIONING SYSTEMS

74

Using Manifold Gauges

The following table describes the connections required for various A/C tests and servicing
tasks.

Low-Side Valve

Center Port

High-Side Valve

System Testing

Closed

Closed

Closed

Discharging

Open

Connect to a
refrigerant recovery/
recycling system.

Open

Leak-testing

Closed

Connect to a
refrigerant supply.

Open

Vapor charging

Open

Connect to a
refrigerant supply.

Closed

Guidelines

•

Close the shutoff valves before removing them from the service ports.

•

Keep the gauge shutoff valves closed when not in use.

•

Connect the gauge hoses to a recovery unit and remove any refrigerant from them after
every use.

•

Make sure that the shutoff valves are within 12 inches of the service valve.

•

Never vent R-12 or R-134a into the air. Always use a recovery system.

Evaluating Gauge Readings

Temperature and humidity affect the pressures you record with the manifold gauge.
Pressure on a hot day will be higher than on a cold day. Check the manufacturers'
specifications for normal pressures at various temperatures.

Air Conditioning Fundamentals

TC070-05-01S

10 – SERVICING AIR
CONDITIONING SYSTEMS

75

FIGURE 39. To
safely and properly
repair an A/C
system, you must
use a refrigerant
recovery and
recycling station.

Refrigerant Stations

Since refrigerant can never be released into the air, you must use
special equipment to recover and store the refrigerant. Figure 39
shows a typical refrigerant recycling / recharging station, often called a
charging station.


















This type of station performs several tasks, including:

•

Recovering (or discharging) refrigerant from the system

• Recycling

refrigerant

•

Evacuating the system of moisture

•

Vacuum testing the system for leaks

•

Charging the system with refrigerant

Air Conditioning Fundamentals

TC070-05-01S

10 – SERVICING AIR
CONDITIONING SYSTEMS

76

Recovery

The first step in repairing an A/C system is to remove the refrigerant from the vehicle and
store it in the refrigerant tank. This operation is known as recovery. During the recovery
process, both refrigerant and oil are collected from the system. The oil must be drained and
measured for replacement with new oil later.

Note: In an orifice tube system, the accumulator may store liquid refrigerant, which may be
difficult to recover. The recovery process can be improved by making sure the engine is at
normal operating temperature. Keeping the system temperature up helps prevent liquid
refrigerant from being released suddenly from the accumulator.

Once refrigerant has been recovered, the station will display the weight of the refrigerant
that was removed. Note the weight or quantity of the refrigerant removed because this can
indicate leaks or overcharging. Open the vehicle’s A/C system only after recovering the
refrigerant.

Recycling

Many recharging stations also recycle refrigerant. As the refrigerant is collected, it is run
through a filter-dryer unit that traps particles, acid, and moisture. This ensures the stored
refrigerant is of the best quality.

Evacuation

After repairs have been performed, or if a system has been open for a long period of time,
the system must be evacuated to remove moisture and ensure that it will hold a vacuum.
The minimum time any system should be evacuated is 15 minutes. The longer the
system has been open, the longer it should be evacuated.

The A/C system is evacuated by creating a vacuum within it. Negative pressure reduces the
boiling point of any water in the system, causing it to turn from a liquid to a vapor. When the
water turns to vapor, it can be drawn out from the system. All water must be removed from
the system, because if water mixes with the refrigerant, hydrochloric acid forms.
Hydrochloric acid is very corrosive and will damage the A/C system components.

Air Conditioning Fundamentals

TC070-05-01S

10 – SERVICING AIR
CONDITIONING SYSTEMS

77

REVIEW EXERCISE 10

Fill in the words that complete these sentences correctly. Check your answers with the
answer key on page 80.

1. When repairing an air conditioning system, you must first _________________ the

refrigerant.

2. Evacuating an A/C system forces any _________________ in the system to boil and

turn to _________________ .

3. When R-12 contacts _________________ , it turns into hydrochloric acid, a very

dangerous substance.

4. Never evacuate a system until removing the _________________ .

5. Recycling removes _________________ , _________________ , and

_________________ from the refrigerant.

6. Pressure readings on a manifold gauge are affected by _________________ and

_________________ .