MAINTENANCE, SERVICING, AND SAFETY:GENERAL SAFETY PRECAUTIONS

GENERAL SAFETY PRECAUTIONS

Cylinders

Refrigeration and air-conditioning service persons must be able to handle compressed gases. Accidents oc- cur when compressed gases are not handled properly. One of the first rules is that oxygen or acetylene must never be used to pressurize a refrigeration system. Oxygen will explode when it comes into contact with oil. Acetylene will explode under pressure, except when properly dissolved in acetone as used in commercial acetylene cylinders.

Dry nitrogen or dry carbon dioxide are suitable gases for pressurizing refrigeration or air-conditioning systems for leak tests or system cleaning. However, the following specific restrictions must be observed.

Commercial cylinders contain pressures in excess of 2,000 pounds per square inch of nitrogen (N2) at nor- mal room temperature. Commercial cylinders contain pressures in excess of 800 pounds per square inch of carbon dioxide (CO2) at normal room temperature. Cylinders should be handled carefully. Do not drop them or bump them. Keep cylinders in a vertical position and securely fastened to prevent them from tip- ping over.

Do not heat the cylinder with a torch or other open flame. If heat is necessary to withdraw gas from the cylinder, apply heat by immersing the lower portion of the cylinder in warm water. Never heat a cylinder to a temperature over 110 degrees F (43 degrees C).

Pressurizing

Pressure-testing or cleaning refrigeration and air-conditioning systems can be dangerous! Extreme caution must be used in the selection and use of pressurizing equipment. Follow these procedures:

1. Never attempt to pressurize a system without first installing an appropriate pressure-regulating valve on the nitrogen or carbon dioxide cylinder discharge. This regulating valve should be equipped with two functioning pressure gauges. One gauge indicates cylinder pressure; the other indicates discharge or downstream pressure.

2. Always install a pressure-relief valve or frangible-disk type of pressure-relief device in the pressure supply line. This device should have a discharge port of at least 1/2 inch National Pipe Thread (NPT) size. This valve or frangible-disk device should be set to release at 175 pounds per square inch gauge (psig).

3. A system can be pressurized up to a maximum of 150 psig for leak testing or purging.

Tecumseh hermetic-type compressors, for example, are low-pressure housing compressors. The compressor housings (cans or domes) are not normally subjected to discharge pressures. They operate instead at relatively low suction pressures. These Tecumseh compressors are generally installed on equipment where it is impractical to disconnect or isolate the compressor from the system during pressure testing. Therefore, do not exceed 150 psig when pressurizing such a complete system.

4. When flushing or purging a contaminated system, care must be taken to protect the eyes and skin from contact with acid-saturated refrigerant or oil mists. The eyes should be protected with goggles. All parts of the body should be protected by clothing to prevent injury by refrigerant. If contact with either skin or eyes occurs, flush the exposed area with cold water. Apply an ice pack if the burn is severe, and see a physician at once.

Refrigerants

R-12 refrigerants have effectively been replaced in modern air-conditioning equipment with R-134a or any of the other approved substitutes, and R-22 has some acceptable substitutes also. They are considered to be nontoxic and noninflammable. However, any gas under pressure can be hazardous. The latent energy in the pressure alone can cause damage. In working with R-12 and R-22 (or their substitutes), observe the same precautions that apply when working with other pressurized gases.

Never completely fill any refrigerant-gas cylinder with liquid. Never fill more than 80 percent with liquid. This will allow for expansion under normal conditions.

Make sure an area is properly ventilated before purging or evacuating a system that uses R-12, R-22, or their equivalents. In certain concentrations and in the presence of an open flame such as a gas range or a gas water heater, R-12 and R-22 may break down and form a small amount of harmful phosgene gas. This poison gas was used in World War I.

Lifting

Lifting heavy objects can cause serious problems. Strains and sprains are often caused by improper lifting methods. To avoid injury, learn to lift the safe way. Bend your knees, keep your back erect, and lift gradu- ally with your leg muscles.

The material you are lifting may slip from your hands and injure your feet. To prevent foot injuries, wear the proper shoes.

Electrical Safety

Many Tecumseh single-phase compressors are installed in systems requiring off-cycle crankcase heating. This is designed to prevent refrigerant accumulation in the compressor housing. The power is on at all times. Even if the compressor is not running, power is applied to the compressor housing where the heating ele- ment is located.

Another popular system uses a run capacitor that is always connected to the compressor motor windings, even when the compressor is not running. Other devices are energized when the compressor is not running. That means there is electrical power applied to the unit even when the compressor is not running. This calls for an awareness of the situation and the proper safety procedures.

Be safe. Before you attempt to service any refrigeration system, make sure that the main circuit breaker is open and all power is off.

Steam and Hydronic Line Controls:Balancing Valves,Valve Adapters, and Filters

Solid-State Devices:The Unijunction Transistor

The Second Law of Thermodynamics:The Entropy Balance

Special Applications:Occupant Controlled Windows with HVAC

SOLID-STATE DEVICES:TESTING THE DIODE

Steam and Hydronic Line Controls:Balanced-Pressure Thermostatic Steam Traps

Steam Heating Systems:Gravity Steam Heating Systems

Motors:The Shaded- Pole Induction Motor

SAFETY ON THE JOB:PRESSURIZING