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!

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!

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.

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

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

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!

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.