Working With Compressors

Whenever working on compressors, look at crankcase oil sight glass reservoirs for proper oil level.  If it is below 1/3 full, add oil; if greater than 2/3 full, think about draining the excess.   If the oil is foaming excessively, then evaluate if any problems exist.

Once a year, when possible on larger compressors, perform an acid analysis of the oil.  If heavy acids exist drain the oil and install fresh oil.  Fill to a ½ sight glass or manufacturer’s recommendations. 

Never take ohm measurements or continuity checks on compressors until you confirm that all power is off, including the crank case heater.  Always lockout and tag out the electrical supply.

Cut out or unbolt the compressor.  Never use a torch to remove the compressor because the oil could ignite and start a fire.  The pressure in the system should be 0-2 psig before opening the system. 

Never run a compressor that is under a vacuum; this can cause arcing internally to the terminals and damage the compressor.  Nor should you run a compressor until they discharge service valves are open to the system.

If you would like more information, contact your local refrigeration supply house and request technical service manuals for any compressors you expect to be maintaining or repairing.  Always reference the service manual for trouble shooting and standard procedures.  If there is no technical information available, contact ARI for the compressor manufacture’s phone number and address and request literature from the manufacturer before experimenting on unfamiliar equipment.

Several compressor manufactures offer 3 – 5 day factory training seminars in various regions during the year.  Consider attending these every few years to stay current with new product releases and service information.

Zone Control Systems On The Job

Zoning should be based on separating the areas of the building depending on how they are used.  Common examples of this would be the bedrooms being in one zone and the living areas in another zone in residential building.  In a commercial building you would want to consider the directions the building faces.  Common examples of this would include the south side of the building being in a separate zone from the north side.

On The Job Example

When your customer complains about handing trouble closing their house door on zone control system, this indicates that the pressure-relief device is either not working properly or is not calibrated.  To test the static pressure on the unit, install a U-tube manometer in the supply duct work and operate the systems.  Go to all of the zone-control thermostats and set them to close down the dampers.  Inspect the static pressure with the dampers open and closed.

When they are closed, the pressure-relief dampers should open up to allow the pressure to escape to a secondary location.  If this does not happen, check the manufacture’s specifications to verify proper operation and maintenance procedures.  Never manually disconnect or force the relief dampers open because this will prevent the unit from delivering adequate air during heavy load periods.

Here's a helpful website on zone control systems that includes a useful graphic.

The Refrigeration Cycle Is All Around You

Maybe you have never taken notice, but the refrigeration cycle is taking place all around you.  If you are an HVAC technician or learning how to be one, this can be a great time to learn more about this cycle if you just start paying attention everywhere you go.

Start looking for the major refrigeration components in every aspect of your life.  Go into your kitchen and observe the refrigerator.  Notice the type of evaporator.  Is it finned, forces air, or automatic defrost?  Feel for the heat rejection from the condenser.  Is it coming from underneath or around the back?  This will indicate if it is using a forced air cooled condenser or a static cooled. 

Next time you go to your local grocery store, observe the coolers in the medium temperature and frozen foods section.  Look for case thermometers, drain lines, ice buildup, and pipe chases.  Listen for any noises associated with the equipment.  Try to locate where the mechanical room and all the compressors are.  Are there any units which are self-contained?

Observing and listening wherever you are will give indications of the refrigeration and air conditioning system.  This includes convenience store, offices, and department stores.  Look for ductwork, piping, thermostats, coolers or any other equipment associated with the mechanical refrigeration and air conditioning systems in the building.  The methods modern building owners use to conceal their mechanical systems and equipment will sometimes amaze the intelligent observer.

Electrical Circuits

Before troubleshooting electrical circuits, the technician needs to learn to first visually check the obvious conditions.  This includes inspecting the thermostat to verify if it is on and adjusted to trigger the circuit.  Next, the technician can check circuit breakers and disconnects.  If all appears usual, the control panel should be opened to check the equipment and fuses.

When it becomes time to check the electrical circuit using the diagram, troubleshooting can be easier if the technician simplifies the circuit to three major areas:

• Line voltage
• Low voltage
• Thermostat control

This means to first locate on the schematic the thermostat circuit and analyze it.  It is the primary control and without it nothing else will work.  Using the voltmeter will immediately determine if the control circuit is sending a signal to the unit.  Next, check the line voltage side of the transformer and the secondary side of the transformer for control voltage.  If all appears normal as expected, then begin to jump through the circuit looking for open switches or failed components.  Remember, an open switch will read potential voltage difference and a closed switch will not. 

Good preventative maintenance while working on electrical controls includes inspecting for loose wiring, work connections, and dirty or pitted contacts.  Wiring and connections should be repaired, but contacts which are pitted should be replaced.  Occasionally, a dirty contact can be cleaned with an industrial-grade contact solvent, but this is often only a temporary fix to keep the equipment running.

Whether you live in Loudoun County, Fairfax County or Manassas, HVAC inspections and electrical testings must be done regularly.

Practicing Safety With Tools And Equipment

It is extremely important to observe safety procedures when you work with electrical and mechanical refrigeration equipment.  Do not work on electrical equipment with live power applied while standing in puddles of water.  If you must work in equipment in wet, moist, or humid conditions, turn off the power first. 

Use insulated tools and rubber gloves to take off covers whenever chances are high for electrical shock.

When using electrical test measuring instruments, be sure to only touch the rubber test probes with your hands.  If possible, keep one hand behind your back, ground one end with an alligator clip, and use the other hand to test the electrical circuits.  In case of an accidental electrical shock, this will help to prevent electricity from going through your heat.

Inspect power tools for worn electrical cords or poor grounding.  When an extension cord is required, be sure to ground the equipment.  Avoid using small gauge extension cords.  They create too much voltage drop and generate heat, thus overloading circuit protectors.  Don’t use accessories that convert three prong plugs into two prong adaptors.  They do not provide the necessary grounding required for electrical safety.

Test equipment and electronic instruments such as gas analyzers, power meters, vacuum pups, and gauges that need maintenance and calibration on an annual basis.  If these instruments have been used rigorously, they may need to be checked twice a year. 

Tools needing maintenance usually need to be shipped back to the manufacturer’s factory or dealer.  Seasons when work is slow can be the best time to do this.  Equipment that is not properly maintained is prone to damage and can shorten the life span of the tools.  It is best to develop a “testing schedule” to rotate all tools and equipment that should be checked regularly.