TEST METER SAFETY

Choosing the proper meter and leads are very important to the success and safety of the HVACR technician. Always choose a meter that has the highest category rating that you can afford. This is preferably a CAT 4, 600v rating. Make sure that the test leads carry the same for your personal safety.

For more of this information on choosing the proper test equipment, obtain the series of the Technical Institute Manuals, available at the ONLINE STORE at RSES.

WHAT ARE AIR CHANGES?

An air change is how many times the air enters and exits a room from the HVAC system in one hour. Or, how many times a room would fill up with the air from the supply registers in sixty minutes.


Engineering room airflow may present a real challenge when balancing an HVAC system. Most calculations only use the heat loss or gain of a room to decide on required airflow and often don’t take into consideration required room ventilation needs. Let’s take a look at how an air change calculation may simplify this step in your air balancing.

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DUAL-PRESSURE PNEUMATIC SYSTEMS

The source of air in a typical pneumatic system is an electrically driven air compressor. Most pneumatic systems can be serviced with a compressor sized under 10 horsepower. The most efficient air compressors in this size range are piston-style reciprocating units.

Regardless of the design of the compressor, the need for clean, dry, and oil-free air is essential to ensure that the air lines, controllers, switches, relays, restrictors, and other components in the system remain clean and operate satisfactorily. For this reason, a number of related devices, such as coalescent filters and refrigerated driers, are necessary in a system to remove any oil vapors and dirt particles and to dry the air. Even the use of oil-less air compressors does not guarantee that oil will not be present in the system. Often, the compressor intake air may con~ oil vapors that can pass through the compressor and condense into harmful droplets in the system if removal devices are not employed.

TO UNDERSTAND MORE ON THIS SUBJECT, GO TO THE ONLINE STORE AND OBTAIN YOUR COPY OF TECHNICAL INSTITUTE MANUAL 3.

THE INHERENT PROTECTOR

Suppose you are testing a Copeland 3D (Discus) compressor and your ohmmeter registers OL from line to line on all of the 3-phase legs. The compressor is cold so you determine that the compressor is not off due to an overheat/internal thermostat trip. Your early assessment is that the compressor is bad and must be replaced. You call your supervisor who immediately sees a red flag when you say all 3 windings are open. It may be a defective “inherent protector”. This happened to a service tech that I supervised a few years ago. And it did have a bad protector.  Please see the following photo and wiring diagram for more information on how this all works and the numbers needed to obtain a replacement inherent protector. By the way, this part is located beneath the terminal plate and is mounted just above the motor windings in order to detect the first possible overheat situation.