I have a unique problem that I can’t seem to correct. I have a background in auto air conditioning so I know what’s going on with the a/c principals overall…i.e. what the components are, why they work, and what needs to be done for seasonal service…but I’m by no means a home HVAC guy. I’ve had several service men come out to take a look at our home HVAC unit but none of them can seem to get the cooling correct. I know everyone says their air conditioner is not cooling but mine does cool somewhat but it’s not very efficient at all and the temperature that’s coming out of the vents isn’t very cold…it is cool, but not cold like it should be. If it’s 70-80 degrees outside or so…then the home HVAC unit cools fine…temps over that, then you can forget about it cooling down to a comfortable temperature even over night when it should be easier to cool. My window A/C units that I’ve had to use to offset the heat in the house, put out twice the cold air out of the registers than my central HVAC unit. Granted, the windows units do not have to go through all the duct work and stuff the HVAC does. The windows units are the only thing that’s really keeping us going already this summer. I live in Texas, so it’s very hot during the summer here. Before I sink more money in it, I’d like to hear what other have to say about this. Does anyone have any ideas here on what could be causing my home HVAC not to perform efficiently?

A little back ground on my system:
I have a split system.
-The outside unit is a Bryant – it’s a 3 ton unit something like 33,000 BTUs. I don’t have the exact model number with me at the time of writing this, but I can get it if it’s needed.
-The inside air handler is a Lennox. It’s a down flow system with registers in the floor of the house. It’s a electric/gas model that in a small closet in the central part of the house. The blower motor, heater (which is gas), and original evaporator are older…they came with the house when I got it. I’m guessing here it’s matched to the outside condenser/compressor unit. Since it was there before I got there, I have no idea what was put in there. Looks like the evaporator or A/C part of the system was a add-on…after the central heat was originally installed. The outside unit and evaporator unit look at lot newer then the rest of the system. The heat will run you out of the house during the winter but the air conditioning is less than desirable.
-air flow itself out to the floor registers is OK…could be better…but it’s fairly strong. The blower motor blows through the gas heater part of the system to get through to the evaporator and then out to the floor registers.
-The supply air inlet is strange….(not sure if this is the correct wording for this part of the system)…let me explain, this is the part where the blower motor sucks air from the interior of the house and passes through the air filter before it goes to the system. What the original installers did here was drop the ceiling gown about 10-12 inches and made an air chamber with suction vents in every room so the air in the entire house is actually turned over.
-It had a slow leak in the system somewhere. No one could find it…it was suggested it’s probably the evaporator core (more on this later).
-I had one installer say that that the condenser didn’t seem to pull enough heat away from the house. I’ve felt it and the air that it blows out is warm but not hot like I’ve observed in other houses.

What I’ve done so far:
-Changed the filter regularly usually after 600 hours of use.
-The inside blower motor ahs been inspected and works fine. Air flow as mentioned above is fair through the system so I don’t think it’s a duct problem.
-The outside unit has been inspected- the fan motor on the condenser/compressor spins fine…starts and stops as the compressor kicks in. During the first part of the year when I was checking the system it was slow to start a little bit but it seems to work fine now. I might need to replace this motor and capacitor going forward.
-The condenser fins has been cleaned several times.
-I have not checked the electrical part of the outside condenser/compressor system but it does seem to work so I haven’t gone any further. Like I mentioned earlier, if it’s 70-80 degrees outside or so it cools good above this . Techs have looked at it and they haven’t said anything.
-I just had the evaporator replaced yesterday since an installer stated that that was the source of the leak or the coil could be dirty preventing it from cooling correctly. It’s an evaporator for a 4 ton Lennox unit and a orifice was put into it to make it work with the smaller 3-ton compressor. I plan on upgrading everything to a 4 ton unit when we have the funds. I thought my prayers would b answered with a new evaporator but I was wrong. First, I thought it might be the orifice may have been installed incorrectly but I should be seeing the compressor cut or the relief valve off from too much of a load if it was. With that said though, my old evaporator in the house had the same issue. So, I don’t think anything was actually done during the new evaporator install that changed anything significantly.
-Small (high side) copper line is hot to the touch
-Large (low side) copper line cold and has condensation.
-Freon level checked frequently but especially verified yesterday with the new evaporator core install.

Phew! Lots of typing and info there. Does anyone have any ideas here as to why my system is not cooling efficiently? I know they say that it’s only supposed to cool the inside temp like 20 degrees from the outside temp but even during the night, it doesn’t. It just can’t keep up when temps are really above 85 degrees. The air that’s coming out of the floor registers is cool but not very cold like my window units. I'm not sure about this, but is outside air supposed to enter the system somewhere?. I don't know if that if happening. I just can’t seem to figure out why it will not cool the house when everything appears to be working. Any help or advice would be greatly appreciated. Right now, I'm dazed, confused, and hot.

Thanks
Steve

Steve - First I'd call and complain very heavily at the folks who soaked you for the new condenser! And then I'd call someone who is knowledgeable about you inside/outside system. The units that run on top of a gas furnace can be tricky.

Or - you could move to where it isn't so hot in the summer (just kidding).

In the return air plenum that you said was dropped 10 to 12 inches from the ceiling. Is the ceiling space above the original ceiling the attic of your home or do you have a two story?

It’s just a one story home…in essence; it’s like a dropped ceiling just in the hallway. It’s not in the attic space; it’s actually inside the home itself. If you take out one of the air plenum vents in one of the rooms, you can actually see the old ceiling as the top of the air plenum. They used the old ceiling as the top of the plenum and put two sides on it which are at each end of the hall in both directions…and made the bottom look like the old ceiling. All together I’d say the air plenum is something like 20 ft long, 6 ft wide, and about 12 inches or so height. It’s like a rectangle. You don’t even notice it’s there; it just looks like the ceiling in the hallway is a little lower than the rest of the house.

I've called in air conditioning specialist a couple of times and explained to them what's going on with it…and to see if they knew something that I was missing. The main problem I'm having in calling in the pros in my area is I get a lot of inexperienced a/c techs who really don't understand what's going on there. A few haven't even seen a system like that. It seems most a/c companies are sending out inexperienced techs who basically just want to put Freon in the system and leave. Of course that’s probably the majority of their work that’s going on right now. The first thing they want to do it say "you need a new system"... and I might, but I'd like to know what's wrong here so I won't have to sink a lot of money in it and have the same problem. In my mind (and that may be the problem), what I have here should be working. The air gauges that techs are using on the compressor are saying that everything is fine. I guess I need to keep calling around to find a better a/c company... but it costs every time they come out.

That drop area can cause a problem. You have to be sure it is sealed properly to prevent the heated attic air from being sucked into the home. Attic air is really hot especially in the afternoon and evening when it is heat soaked.

The attic heat will also radiate down from the drywall that is attached to the ceiling right below the attic. It has been many years ago but I had a similar problem on a job so I just thought I would mention it.

Thanks! I appreciate any and all suggestions. I will definitely check that out.