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 

_________________ .