Two for One???

I am looking for some enlightment regarding what I found, or at least think I found, on an inspection yesterday. I am relatively new in the business (two + years) and I haven’t run in to this before. House had split AC system with evaporator coil, horizontal-flow furnace & air handler unit in the attic. What has me perplexed is that there are two air conditioner condensing units (ACCU’s) outside for this single system. One ACCU is 1½ ton and the other is a 2½ ton. Is it possible to have two working ACCU’s for a single evap coil? How does this work? I have never seen anything in literature about this arrangement. If anyone out there knows what this is all about, I would appreciate a shout.

Thanks much,
Gary Loughman
Assured Home Inspections, Pllc

Did you see 2 sets of refrigerant lines in the attic? I doubt that a single evap coil would have 2 condensing units in a residential setup. There might be 2 coils in parallel, providing 2 stages of cooling, though. If you didn’t see both sets of refrigerant piping, then there may be a coil at another location for a separate zone.

Jim King

Looking at my digital picture, I am only seeing one set of refrigerant lines at the coil location. This is a small one story place and there is only one zone. Outside , each ACCU has there own refrigerant lines that enter the house going to the attic. I am sorry that I haven’t figured out how to send the picture along with my message.


If two sets of lines are entering the house, and you only saw one set in the attic, then the other set must be going somewhere else. Perhaps to a wall mounted unit in the master bedroom?



No wall units anywhere. I may try to go back and look this over a little better than I did the first time. Because I hadn’t seen anything like this before I should have been more of a detective to find out more about what I was looking at.

Thanks for your help.


If you’ve got two Condensers, you got to have two air handlers. The attic unit usually conditions the upper floor. There’s got to be another air handler in the lower crawlspace/basement area somewhere.

Are these two Condensers the same age?

Not necessarily. Many years age FEDDERS developed a dual coil that fit into a single furnace/air handler, but was operated by two condensing units. It was controlled by a thermostat with two mercury bulbs that would make connection 2 degrees apart. If the first system could not cool the house, the temperature would rise 2 more degrees and activate the second condenser.

Frequently the two line sets were joined in a common conduit and appeared to be a singe installation inside the house.

There was also an occasional attempt to use two small condensers in place of a larger unit (sometimes the cost difference was enough to do this) by joining the two lines into one larger line set. There were about 200 reasons why this didn’t work, but you never know until you try.

Was that the side by side evap unit?

To David Valley,
Thanks, but there is only one floor, 1,144 sq.ft., on pier & beam.
ACCU’s are same age.

To Jae Williams,
Thanks, I thought I was going nuts or something.

Gary Loughman

Hmmm…Never seen such an animal in my area.

You’re not off the hook yet. You definitely have an additional air handler somewhere.

You stated…

So the other set of pressure lines are going somewhere!!!

Four tons of cooling is way too much for 1,144 SF, even in hot, humid Houston. I suspect one of those condensers was abandoned when replaced by the other.

Jim King

James is correct, thats way too much cooling for that size home even in Texas. Did you run the ac units to see if they both ran at all.Without seeing the set up,I would go with possible abandoned unit also.Matt

My 1st question is did you try to operate the AC system with automatic controls? If you did, did both condensers operate?

If there is no 2nd air handler in the house, then consider the possibility that the AC had been swapped out at one time or another and whoever did the changeout didn’t remove the old condenser. Just a thought.

My “go to guy” in HVAC, considered one of the very best in the business, lived in the Cinci area, and was the FEDDERS trouble-shooter nationally. I think the pilot program for those units was centered around him. I know he didn’t think much of the concept, but made a concerted effort to make them work.

I don’t know if the system got too far away from the mid-west.

Yes, sometimes they were called that. “Duo-flex” was the registered trade name.

The coils were occasionally joined for custom usage–1 1/2 ton on one side, 2 1/2 ton on the other. Or various other mixes. The factory supplies, though, were generally matched by size.

Guys two condensing units one evaporator is common in light commercial HVAC and very common in commercial refrigeration but not in residential very unusual. But time has taught me to expect the uncommon in this HI business.

I would be very shocked to find two condensing units on one evap in a small residential unit unless the past owner was in the HVAC business and designed his own controls which would also require an oil separator to keep one condensing unit from robbing oil from the other unit which is a common occurrence with that type of set up.

I would have to think someone just left an abandoned unit. As Tony N. would say NEED PICTURES MORE THE BETTER.


Gary stated that both units are the same age.

Ok I still need Pic’s As you know David anything is possible


I’m a little confused with your terminology, as you describe what you were seeing. I’m not critisizing, just trying to get a clear uderstanding of what’s existing.

Attic installation - Minimal height and /or working space ?
Horiz. Nat.Gas Furnace (1) - ?
Horiz. designed Evap. Coil (1) - ?
Outdoor Cond. Units (Cooling only or Ht. Pump?) (2) - ?

Split or 2 staged or Circuited evap. coils were/are still used for a lot of light commercial construction today, according to a friend of mine in the business.
I use to design and spec them in the 70’s and 80’s, some even in residential situations, although those systems were usually reserved for higher end properties (local mansions ?).
I know Texas is hot, but 11/2 AND A 21/2 ton on 1100-1200 sq.ft.?? I hope you recommended to your Client, that further investigation was warrented by a Prof. HVAC Contr., for analysis and recommendations.

Good Luck