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December 3, 2017

The Importance Of Seeing The Whole Picture

The NETTTS school here in Pawtucket, RI offers both Commercial Driver’s License and HVACR Technician career training, so as one of the HVAC Instructors I recently got a phone call about one of the buildings on campus having trouble with their air-conditioning. My students in the HVAC-R program were excited to test their new skills out and tripped over each other to get a piece of the action. We walked over to the other building and quickly discovered that the condenser fan was not moving, and the compressor was piping hot. AHH we thought, That must be it.

After installing the new condenser fan motor, we started the unit and were on our way….until the phone rang. Still no cooling. The class again rushed over to play hero. Everything seemed to be running, but the air from the supply vents was the same as the air entering the return. It was time to hook up our manifolds! And when we did, imagine our surprise when we had no pressure difference. The compressor was running but not compressing the refrigerant. Knowing that the unit had a reciprocating compressor, we made a guess that the connecting rods had broken from the crankshaft and the motor was still turning. The unit looked like it was going to be replaced soon anyway so we installed a new condensing unit the next day, Case closed, right?

A few weeks later someone noticed the suction line on the new condenser was all iced up.  What was going on? Again, the students and I all rushed over to the other building and when we threw our gauges on, it seemed like it was low on refrigerant. We knew we didn’t have a leak as we pressure tested and drew a vacuum of under 500 microns. When we charged the unit our pressures and superheat were dead on. What could be the issue? The filter! Onward to the filter! As we pulled the filter out we could clearly see we had forgotten to check it when we installed the new condenser.

And then a thought came to me. I have replaced a few older air conditioning systems recently and one of the things that struck me was how dirty the evaporators were. They seem to have all had a film of hair and dust on the intake side of the coil. It didn’t matter that the units were owned by one owner families, and that they were religious about the cleanliness of their homes, and fanatics about changing their filters. In each case I found the same thing. Taking this thought and sharing it with my HVAC students, we thought it would be best to examine the evaporator coil, just to make sure! And what do you think we found? Dirty coils.

After we cleaned the coil, and replaced the filter, the pressures stabilized to a more acceptable range. It was a great experience for the heating and cooling students at our HVAC School. It also suggests that hindsight is a great lens for seeing the whole picture.