Figure 1. (Click on the image for an enlarged view.)

In this troubleshooting situation you have inherited a service problem that goes back to last year’s cooling season… residential HVAC equipment that’s seven years old with a lot of history, and repeated trips in response to complaints that this split system that employs a horizontal, attic-installed gas furnace “just won’t keep the home comfortable.” Several different technicians have been involved, and all of them have focused on the sealed system as the source of the problem, with diagnoses ranging from an undercharge, to kinked tubing in the wall, to an inefficient compressor. Since the majority of the complaints, which have been lodged by the various tenants of this three-bedroom, two-bath rental, have been about uncomfortable temperatures in the summer (the mild winter climate hasn’t generated many requests for service), you’ve been asked to do whatever needs to be done to solve this situation.

When you arrive, you note that the outdoor ambient temperature is 80°F, and when you inspect the air-handling system in the attic, you find that the methods employed in the installation have made it extremely difficult to access the “A” coil, but you are able to make the necessary gauge connections (the HP hose for a high pressure reading at the air entering the coil and the LP hose for a low pressure reading at the air leaving the coil) to test the pressure drop across the coil. (See Figure 1.)

After allowing the system to operate for approximately 20 minutes, and noting that there is condensate in the drain, you begin your pressure test and note that the drop is measured at 0.6 in. wg.

Your troubleshooting question: What is the next step you need to take in order to continue your evaluation of this equipment?

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Publication date:07/04/2011