Is my AC working right?

11 years ago

We've lived in this house for over a year now and have never noticed any issues with heating or cooling. In other words, it has always been whatever temperature we tell it to be.

About a month ago, I noticed that our upstairs AC wasn't working at all. There is an entire unit dedicated to the upstairs. I called a company out, guy came and said condenser fan motor was out. He replaced it, said it was working now, and left. It look about 12 hours for the temperature to get down, but that night it did seem to get to whatever we set it at.

I then started noticing that in the heat of the day (like 90 degree weather), our upstairs AC would never go below 78 no matter what I set the thermostat to. Our downstairs AC (2 units for downstairs) has no problems maintaining as cold as we'd like.

I called the company back out, and the tech basically just inspected the condenser again. He said the system is working fine, and he has no explanation for why it won't cool below 78. He casually mentioned that maybe the ducts need to be rebalanced or we need more insulation, but he didn't offer to look into either of those things. To be fair, he said the attic was too hot for him to be in there, and I agreed with him. I have changed all air filters and the tech cleaned the condenser.

I'm glad that he wasn't saying the unit was broken or undersized, but I am really frustrated by not getting below 78 degrees in the daytime. Even if you try to say they are only designed to go 20 degrees below the temp outside (which I don't think is right, but what do I know), it's still not going 20 degrees down. The tech agreed with me that it's not like I am trying to make it 65 degrees and that 78 is not exactly comfortable.

I am reading such mixed things on the internet. Some people say this is just "the way things are when it's really hot" and others are saying a system should go to whatever temp you set it at, it just may run longer and be more expensive to run than you'd like. What is the right answer? And for what it's worth, I have a very nice, well-built home with no apparent issues with insulation. (We have no trouble getting it toasty warm in the winter)

Featured Answer

klem1

11 years ago

There are a number of possabilities and your questions can only be answered by a compitent tech after inspecting the system. I don't advise you hire a tech and tell him "Klem said" but if you want to takle it yourself and have a few tools and a little experience I'll be happy to tell you the most likly things to test and look for.

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Comments (8)

C F
Original Author
11 years ago
Klem, thanks so much for your comment. Sadly, I am not handy at all, so I doubt there is much I would be able to do with checking the system out myself.

My plan right now is to just wait it out. It has been cool this week, so the system has been meeting whatever temp we set it to. If we have another strong heat wave, I'll have to re-evaluate getting another pro opinion. I'm also going to wait for our next utility bill to see if it's been running nonstop and the bills have gotten out of hand.

Appreciate the help!
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thegypsyrover
11 years ago
Why don't you contact your utility company. Many of them offer free energy audits. They also should be able to answer questions about what is common in your area regarding air conditioning in extreme temperatures. Hope this helps!
mike_home
11 years ago
Where are you located? What is the area of the second floor? Do you know the size of the second floor AC? If not, see if you can get the model number of the outside unit. The size will be coded in the model number.

It could be the AC is undersized when it is very hot outside. Can you go into the attic and verify how many inches of insulation at there? Increasing the insulation could be an easy fix to the problem.
tigerdunes
11 years ago
What is supply temp and return temp? Easy to check with digital thermometer that are available at big box store. I agree about knowing the size of system and size living area expected to be cooled. What is your location? Is system running continuously or is it cycling? Humidity levels? How many returns? Filter has been checked or replaced?

IMO
Vith
11 years ago
last modified: 11 years ago
Things to check:
- insulation levels in attic - not enough allowing easy heat transfer to living space
- attic ventilation - air may not be venting properly in the attic causing super heat
- size of ductwork and type - if you have 4" flex runs that's going to be a huge difference than using 6" rigid
- tonnage of AC condenser - as mentioned might be undersized in very hot conditions
C F
Original Author
11 years ago
Hi all,

Sorry I went AWOL after posting this. I wanted to provide an update for anyone who's interested. A couple of weeks after posting this comment, the AC totally stopped working again.

I called a different company out, and they said the evaporator coil had been leaking freon and was almost completely empty. Because the unit is about 10 years old, we opted to replace the whole air conditioner with a new, more efficient one rather than replace just the coil. I had the unit replaced on Monday. I also paid extra for them to check all of the ceiling ducts upstairs and seal any leaks.

Here it is Thursday and I just went upstairs to see how things are going. The darn thing is reading 76 when I have it set at 75! I called, and the company said that is not normal--it should go below 76. My expectation was it would cool to whatever I set it to (although realistically would never ask it to go below 73). About to deal with them again tomorrow...

To answer some previous questions, it's a pretty big house. The upstairs is probably about 2,000 sq feet and is open to cathedral ceilings in the downstairs. I have no problems whatsoever keeping the downstairs cool. 2 units cool the downstairs. Upstairs is a 5 ton unit. Probably 10 returns. All in the ceiling. All just checked and confirmed clear and sealed. All filters are brand new. We're located in Oklahoma. Temperatures have been pretty high- like 95 lately, but again, downstairs has no problems.

I'll let you all know what they end up saying now! Thanks again for all of your help!
ionized_gw
11 years ago
Was the AC running continuously when you set it to 75 and the thermometer was reading 76? If not, then just set it one degree lower.