NOTE: This is Lesson # 1 from the HVAC Maintenance Recovery Lesson's Page

AIR COMPRESSOR OPERATING INSTRUCTIONS

Due to the high cost of replacement and excellent reliability, many school districts nationwide still have pneumatic temperature control systems in one or more of their facilities. Critical to the proper operation of these systems is a clean, dry, oil-free source of air.

The heart of a pneumatic temperature control system is the air compressor. The following guidelines are intended to help you extend the life of your pneumatic temperature control devices. Operate air compressor systems on a year-around basis. You do not want warm, moist air to enter the airlines when the system is off.

Drain water from the air tank daily, year-around. Make certain that the air is drained from the bottom of the tank, not the midpoint on the end of the tank, through a siphon. Have the drain line from the tank, and the refrigerated air dryer, piped to a container, to keep from having oil spread all over the floor.

Keep an eye on the liquid in your container. Is it all clear water? That's what it is supposed to look like. If it is white or milky looking, this could indicate oil contamination.

The optimum design for a temperature control air compressor is 4 minutes on - 8 minutes off. This extended off time allows the compressor cylinder(s) to cool. This total on/off cycle time adds up to 12 minutes, or 5 on/off cycles per hour.

Compressor systems with more than 5 on/off cycles per hour have a need for further investigation. Either the tank is too small, the compressor is too small, the compressor is wearing out, or the system has lots of air leaks. Again, the compressor cylinder(s) will not cool, if it has frequent on/off cycles. This heats the lubricating oil to the point of vaporizing. As that oil is carried throughout the system, it condenses, plugging restrictors and damaging control devices. Keeping the oil from entering the air lines is much less expensive than removing it after the fact.Another major concern is the run-time ratio. Compressor systems whose on time exceeds the off time either have a compressor that is worn out, too small or the system has too many leaks. Again, oil contamination will result.

No filters should be placed between the compressor tank and the refrigerated air dryer. They will just collect water and cause problems. Pressure reducing valves must be downstream of the refrigerated air dryer and all filters.

Between the air compressor and the refrigerated air dryer, there should be no filters or pressure reducing valves. Moisture is certain to condense at these points, shortening the life of these devices.

A properly sized, good quality refrigerated air dryer is a must. When at the compressor, draining the tank on a daily basis, grab a hold of the outlet of the refrigerated air dryer. It should feel cold to the touch. If the equipment room has a high humidity level, you may even see water sweating from the cold outlet line. If the outlet line isn't cold, get the refrigerated air dryer serviced immediately! Pneumatic temperature control devices cannot tolerate moisture contamination.

The minimum compressor on pressure should be 60#. This allows the air to be in the refrigerated air dryer long enough to cool to the condensing temperature and wring out the moisture.

Clearance between the wall and the compressor flywheel should be a minimum of 14'. This allows the flywheel to operate as a fan and help cool the cylinder(s). Be certain that flywheel rotation blows the air across the compressor. It cools the compressor better than trying to draw the air across the compressor.

Use two air intake filter elements on the compressor. Alternate them twice a year - minimum. More frequently, if the area is dirty. Use a good quality, washable type filters. Put the freshly washed filter in a clean, dry location between changes.

Compressor oil should be changed only once a year. Remove the access plate and clean the sludge out of the bottom of oil sump, at every oil change. For pressure lubricated compressors, clean the oil pump pickup screen at the same time. Be certain to have a new access plate gasket on hand. Replace the access plate gasket, if it was damaged in removal.

Use a good quality, heavy-duty compressor grade oil only. Do not use any type of automotive grade oil. Not even non-detergent. Automotive oil is designed to go everywhere. That's good for cars, but it is not what is needed for temperature control air compressors. When an air compressor fails, replace it immediately with a slow RPM, pressure lubricated compressor, specifically designed for temperature control use. At least one major manufacturer makes their temperature control air compressor with side-seal rings. The ends of the rings are made at opposing angles, so that they overlap. Our experience is that a few extra dollars in a properly sized air compressor of this style, is well worth the investment.

In keeping with our commitment to be respectful of your time, this lesson will be continued next month, when we discuss the after air dryer filters needed to assure a clean, dry, oil-free source of air for pneumatic temperature controls.

* These lessons are brought to you independently of SchoolFacilities.com by Climate Makers, Inc. and are intended to be implemented by experienced HVAC technicians.