At the root of any study that compares human beings to all other animals on earth is the simple understanding that the one thing that makes humans different is their ability to reason. And, of course, that’s a good thing…..most of the time. However, after a lifetime of study of how human beings think, I’ve come to the conclusion that, in certain situations, due to the ability to reason, people sometimes uncessarily complicate somethng that isn’t complicated. For example, I recently presented the following troubleshooting problem, which is straightforward and not complicated:
AN A/C SYSTEM THAT’S NOT KEEPING THE HOUSE COMFORTABLE
In this troubleshooting situation, our customer’s description of the problem is “not cooling” and “blowing warm air”, and the equipment that is supposed to keep this residence comfortable is a split system that has been in service for sixteen years. The service history of this unit includes several electrical repairs, and in one instance, a leak in the sealed system was found and repaired.
When you arrive, you find the following conditions:
- The indoor temperature is near 85-degrees.
- The thermostat set-point is 70-degrees.
- The indoor fan motor is running normally, and you determine that the indoor air flow is sufficient.
When you go to the condensing unit to continue your evaluation, you find that the outdoor fan motor and compressor are operating on this R-22 system, and, after confirming proper air flow through the condenser coil, you measure an ambient temperature of 90-degrees. When you connect your gauges to the high and low side access valves, you read the following pressures.
- Low-side pressure: 90 PSIG.
- High-side pressure: 170 PSIG.
To complete your diagnosis, you apply the pressure readings to the temperature scales on your gauge set, and you also measure the current draw of the compressor as lower than normal.
Your troubleshooting question: What is the specific failure that is preventing this system from cooling properly?
I received a variety of answers to this question, most of them incorrect. And, like I said, I’m convinced that the underlying reason for this is the tendency of people to complicate something that is straightfoward and simple. In this case…..troubleshooting an HVACR system that’s not performing as it should…. the simplicity lies in two fundamental processes:
1. Troubleshooting is always a systematic elimination of the possibilities.
2. Knowing what right is in the first place so you’ll know what wrong is when you see it.
On the first point, we accomplished a lot of elimination in the description of the problem. The indoor air handler was operating…indoor air flow was sufficient, which proved that the evaporator coil wasn’t dirty…the the outdoor fan motor was operating and the condenser coil was clean…and the compressor was running. So, we eliminated all of the possibilities in regard to the air flow and electrical systems, which means that the problem lies in the refrigeration system.
And, that brings us to the second fundamental process…knowing what right is in the first place.
In our problem situation, we stated that the low side pressure reading was 90 PSIG. When you apply the fundamentals of the operation of a comfort cooling system, knowing that what you’re looking for is an indoor coil temperature of approximately 40-degrees, and you apply that knowledge to reading the R-22 scale of the gauge, what you find is that the low side operating pressure is supposed to be approximately 69 PSIG.
So, the conclusion here is that our low side operating pressure is higher-than-normal.
Regarding the high side operating pressure, we stated that our gauge showed it to be 170 PSIG. Again, consulting the R-22 scale on a gauge and adding 30-degrees to that figure to allow for the heat of compression (after all we did say that this unit was in service for 16 years, which means that it is a standard efficiency unit, so 30 is the number we add to the amibient temperature to calculate what the high side should be on this particular system), you’ll find that the operating pressure in a 90-degree ambient is supposed to be approximately 260 PSIG.
So, the conclusion here is that our high side operating pressure is lower-than-normal.
And, when you put our two conclusions that are understood from the fundamental perspective of knowing what right is in the first place….a higher-than-normal low side pressure reading and a lower-than-normal high side pressure reading… together, along with the other fact we stated (the current draw of the compressor is lower than it should be), the diagnosis is that the compressor is not working due to a valve failure. When comperssor valves fail to seat properly and no longer internally separate the low side from the high side, the compressor cannot pull down properly on the low side, nor discharge properly on the high side. In essence, it’s “not pumping.”
A simple and un-complicated conclusion, arrived at by applying the two simple and straightfoward factors we stated above.
Learn from yesterday….Live for today…..Look forward to tomorrow.