Underlying Problems That Get Missed

Today, I ran a service call with another tech where the previous tech had diagnosed an intermittent piston restriction. I read the history beforehand. For the past several years, there were many assorted comfort complaints and a lot of minor charge adjustments in both the summer and winter. It is worth noting here that the system, like many in our market, was a heat pump.

There were mentions of freeze-up during the summer and high-pressure cut-out during the winter, which had me thinking it was an airflow issue even before we arrived.

As we pulled up, I noticed it was a townhome community with four homes per building.

There was no tenant home, so we accessed the home via lockbox, and as we walked up the stairs, I noticed the home was quite small, with two bedrooms and two baths. When we opened the air handler closet, it was… 3.5 tons.

The place had 12″ x 12″ tiles on the floor, and it was a simple rectangle, so we counted up length x width, and the entire home was just under 1200 sqft.

Now, sqft per ton is no way to do a load calculation, I admit it.

But this townhome had occupied spaces on both sides, meaning the only exposures and windows were on two sides, with big trees shading the back. The building was built in 2007, and this system was installed in 2016.

What's the next move you would make?

Common Sense

The great thing about having four other near-identical units on the building is that we can easily see what tonnage they had installed, and they were 2-ton units. Makes more sense.

So, in 2016, some fly-by-night company hacked in a 3.5-ton unit rather than using a 2-ton that may have been a little oversized in the first place, given the low loads on this home.

The result is a system that is running REALLY low airflow, resulting in low evap temperature and low superheat in the summer and high head pressure in the winter. Techs had tried to “fix” the problem each year with little charge adjustments rather than finding and fixing the underlying issue.

After walking around the home, we found some vents closed—likely because they were blowing somebody's wig off with the high air velocity.

We went into the attic and found some ducts unsealed, some insulation pushed out of the way, and two bath fans venting freely in the attic.

None of this required fancy tools or advanced diagnostic techniques to diagnose, just some common sense, some looking around, and a little comparison to figure out the story.

Elementary, my dear Watson. Elementary.

—Bryan

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Related Tech Tips

Checking Evaporators on Furnaces
In Florida, there are not many gas furnaces—at least not as many as up north. Sometimes, we can look like real dummies compared to techs who work on them every day. One thing to know about 80% gas furnaces with cased evaporator coils is that you can often check the evaporator coil by removing the […]
Read more
First Law of Thermodynamics
The first law of thermodynamics is an extension of the law of energy conservation. The latter states that energy can be neither created nor destroyed but converts from one form to another. Thermodynamics is the study of heat’s relationship with mechanical work, and it establishes heat as a form of energy that can be neither […]
Read more
Don't use Tank Caps on Systems
This is a video tech tip from our friend Brad at HVAC in SC. In this video, Brad demonstrates that using a cap off of a refrigerant tank on a system can depress the Schrader core on the system in some cases. Make sure to use proper caps that have seals or brass flare cones. […]
Read more
loading

To continue you need to agree to our terms.

The HVAC School site, podcast and daily tech tips
Made possible by Generous support from