NOTE: This is Lesson # 2 from the HVAC Maintenance Recovery Lesson's Page
Many of today's refrigerated air dryers have a dirt filter, as an integral part of the water dump mechanism. This operates as a pre-filter, extending the life of the oil filters that follow. To determine whether or not this filter is dirty, there should be air gauges on the entering side of the air dryer and the leaving side of the dryer. Most of the operating manuals indicate that when the pressure drop across the gauges reaches 10#, the filter should be cleaned. Our experience indicates that this is a waste of time. The cost of a replacement dirt filter is minimal. Go ahead and replace the dirt filter, when the pressure drop indicates that it is time.
After the dirt filter, there should be a good quality, coalescent oil filter. Again, this filter requires air gauges on each side to determine the pressure drop. The air gauge after the dirt filter, mentioned above, acts as the air gauge on the entering side of the coalescent filter. The coalescent oil filter is also replaced when the pressure drop between the gauges reaches 10#.
The coalescent filter should be followed by a superior quality, activated charcoal, oil vapor adsorbing filter. This is your last line of protection. Don't try to save a few pennies here. The frequency, with which this filter is changed, is determined by the filter quality and the system air consumption. Your installing contractor, or filter supplier, should help you determine the frequency of changing this filter. As a general rule, even if the air consumption is low, this filter should be changed at least annually. We suggest it be changed when changing the oil on the compressor.
Remember, all of the above filters are to be at high pressure and after the refrigerated air dryer.
Feel the outlet line of the refrigerated air dryer every day. It should feel cold, like a glass of ice water. In the summer, you may even see it sweat, like a glass of ice water. If it's doing that, you don't even have to feel it. If it is not cold to the touch, immediate adjustment, repair or replacement of the refrigerated air dryer is recommended. The key word being immediate. Moisture in pneumatic air lines can cause lots of unpleasant and costly damage.
After all the filters, you will find one, or more, pressure-reducing valves (prv). Some systems have one prv for the day setting of the thermostats and another for the night setting. Any adjustments to the pressure settings must be done when there is air flow through that prv. That is, only adjust the day prv, when in day operation. After switching from day operation to night operation, wait a few minutes to let the system settle out, before making any adjustments to the night prv.
Following every prv, there should be a 30# safety pop-off valve. This is needed, in the event of a failure of the prv. At least once a year, typically when changing the compressor oil, these pop-off valves should be exercised. Wrap the pop-off valve with a brown paper towel. Pull the ring on top of the valve until it blows air at full force. If there is moisture or oil at that point, the paper towel will help keep it from blowing all over everything, including you. It will also help in analyzing what's going on.
If the towel appears wet, set it aside for a while. Later, if the towel has dried to its original color, the dark stain was just water. Get the air dryer checked immediately. If the dark stain is still there, it's oil contamination! Double-check all the filters, replacing as required. If the problem isn't obvious, recheck the compressor run time; the distance between the wall and the flywheel; make certain that the flywheel rotation is correct; and so on. If the air compressor is not properly cooled, it will pump oil.
Removal of oil contamination is extremely expensive. Not removing oil contamination can be even more expensive. Oil contamination can cause poor operation of controls, resulting in lots of comfort and indoor air quality complaints, inefficient operation, constant recalibration and potentially costly replacement of damaged controls. Instead of going to the expense of removing oil contamination, repairing or replacing defective controls, and upgrading the sequence of operation, this where you need to start looking at the big picture. If the pneumatic temperature controls are broken, dirty, and providing poor sequences of operation, you may be better off taking the money needed to refurbish the pneumatic controls and investing in modern direct digital controls.
When a replacement air compressor is needed, do not buy a new compressor that is not specifically designed for temperature control use. We prefer slow speed, pressure lubricated air compressors for pneumatic temperature control work. Properly sized, they can last for decades. Anything less than a properly sized air compressor and storage tank system, specifically designed for temperature control use, will cost you more in the long run. Replacement air compressor and tank assemblies should be sized for one-third run times and five on/off operations per hour. That is, 4 minutes on, and 8 minutes off, is an ideally sized air compressor and tank assembly. This assures that you spent enough, without spending too much.
Finally, keep good records on the compressor run time. It will help to determine the cause of future compressor problems, air leaks and air consumption. If you'd like a copy of the compressor timing information log form that we use, you may print it by going to:
http://www.climatemakersinc.com/lessons/compressor_timing.pdf