Service & Maintenance / Extra Edition

Troubleshooting Challenge: A Comfort Cooling System That's Not Gettin' Down

May 4, 2009
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Figure 1. (Click on the image for an enlarged view.)

This time around we have a customer who has called to say that it’s warmer than it should be in their home. “It’s just not as comfortable as it used to be,” is the way they’re explaining it. When you arrive you find a nine-year-old package unit, and you determine in a short time that, electrically, everything is as it should be, which means that what you have is a unit that is running, but is not cooling enough.

After carefully checking airflow over the indoor coil and making sure that it’s not dirty, and that there isn’t a clogged filter problem, you turn your attention to the refrigeration system. Since this R-22 unit is equipped with a fixed-bore metering device (multiple capillary tube) you implement the use of the superheat method to check the charge. In order to accomplish your evaluation, you employ the chart shown in Figure 1, and plug in the following temperature readings you obtained.

• Air entering the indoor coil: 68°F

• Air entering the outdoor coil: 90°

Figure 2. (Click on the image for an enlarged view.)

As your next step, you check the low-side operating pressure of the refrigeration system and find it to be 61.5 psig, which you plug into the chart in Figure 2 to convert it to a temperature. As your last step in the process, you measure the suction line temperature and find it to be 55°.

With your evaluation tests complete, you proceed to your diagnosis.

Your three-part troubleshooting question:

1. What was the superheat reading supposed to be for this unit?

2. What was the actual superheat of the unit?

3. What is your diagnosis?

Compare your answers with ours by clicking here.

Publication date: 05/04/2009

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