Mazda Training manual - part 274

Air Conditioning Fundamentals

TC070-05-01S

10 – SERVICING AIR   
CONDITIONING SYSTEMS

 

 

 

70

OBJECTIVES 
 
 
After completing this section, you will be able to describe how to: 
 
• 

Use a manifold gauge 

 
• Recover 

refrigerant 

 
• 

Evacuate an A/C system 

 
• 

Test for a leak 

 
• 

Charge a system using liquid or vapor refrigerant. 

 
 
 
OVERVIEW 
 
An automotive A/C system is under pressure and contains potentially lethal materials. 
Recharging an A/C system is not simply a matter of opening the system and adding 
refrigerant. You must take special precautions to prevent accidents. 
 
 
Follow these five steps to ensure a safe and accurate recharge: 
 
1.      Air conditioners have both a high-pressure and a low-pressure side. Use a manifold 

gauge to check the system’s pressures. If either side’s pressure is too high or low, the 
A/C system will not perform correctly, and might explode. 

 
2.   Recover the refrigerant. 
 
3.      Evacuate the trapped moisture in the system. If moisture remains, the system will not 

perform properly and dangerous chemical compounds may form. 

 
4.      Check the system for leaks and repair any you find. 
 
5.      Recharge the system with the correct type and amount of refrigerant. 
 
 
The remainder of this section, discuses each step in detail. 
 

Air Conditioning Fundamentals

TC070-05-01S

10 – SERVICING AIR   
CONDITIONING SYSTEMS

 

 

 

71

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 

 

 

FIGURE 37. A 
manifold gauge is a 
calibrated device 
used for measuring 
A/C system pressure.

 

 
 

Answers to 
Review Exercise 9

 

 

1.  A

 

2.  D

 

3.  E

 

4.  C

 

5.  B

 

 

CHECK THE PRESSURE 
 
 
Servicing an A/C system starts with using a manifold gauge set to 
check the pressure. 
 
The Manifold Gauge 
 
A manifold gauge is a calibrated device used to measure air 
conditioning system pressure. This device allows the technician to 
perform four important tasks: 
 
1. Monitor the pressure inside the operating system. 
 
2. Monitor the flow of refrigerant into the system during charging. 
 
3. Control the flow of refrigerant into the system during charging. 
 
4. Access the system for discharging 
 
A typical manifold gauge set, shown in Figure 37, consists of a center 
manifold and two (or sometimes three) gauges. 
 

 

 
Manifold gauges help determine where and at what pressure to deliver 
refrigerant. The valves open and close passageways to the center port 
and its service hose. 

 

The gauges on either end of the manifold select which system to apply 
to the center manifold area. Although the low pressure gauge appears 
on the left in this drawing, and the high pressure gauge appears on the 
right, not all manifold gauge sets will be oriented this way. 
 

Air Conditioning Fundamentals

TC070-05-01S

10 – SERVICING AIR   
CONDITIONING SYSTEMS

 

 

 

72

Making the Connection 
 
Use one of the following methods to ensure that you connect the manifold gauge correctly. 
 
 

•  Identify the high and low side of the system by tracing the hose from the condenser 

back to the compressor. The compressor connects to the high- pressure side of the 
system. 

 

•  Both R-12 and R-134a systems use connectors of different sizes to help prevent 

connecting the gauges to the wrong sides. Furthermore, R-12 and R-134a system have 
different-sized valves, to prevent accidental mixing of refrigerants. 

 

•  The threaded Schrader valve is the most commonly used service valve, or port, for the 

R-12 system. R-134a systems use larger, metric-thread, quick- connect service valves. 

 

Air Conditioning Fundamentals

TC070-05-01S

10 – SERVICING AIR   
CONDITIONING SYSTEMS

 

 

 

73

FIGURE 38. R-12 and 
R-134a systems use 
different connections 
to the manifold 
gauge.

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
The manifold gauge connects to the air conditioning system as shown 
in Figure 38. 

 

1.      The low pressure gauge connects to the service valve between 

the evaporator and compressor suction port. 

 

2.      The high pressure gauge connects to the service valve between 

the compressor and the condenser. 

 

3.      The center port is used to add and remove refrigerant. This port 

can be connected to refrigerant supply tank, evacuation pump, or 
refrigeration oil canister. 

 

For R-12 only 

        For R-134a only