Thread: A new one on me, 2 ac systems reversed

Just listening to the local homeshow guy. A caller said he had a two story house that was 8 years old and never did cool right downstairs, but the upstairs cooled real good. Said he called an AC guy for service and the AC guy told him the lines were switched. The line set for the downstairs condensing unit was connected to the evap coil for the upstairs unit and vice versa.

I guess I never have really considered this, but it doesnt surprise me now that I think about it.

Anyone seen it before, and how do you check. Turn on the upstairs or downstairs system only and check the airhandler in the attic to make sure its correct and that the proper condensing unit is running?

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Originally Posted by imported_John Smith

Just listening to the local homeshow guy. A caller said he had a two story house that was 8 years old and never did cool right downstairs, but the upstairs cooled real good. Said he called an AC guy for service and the AC guy told him the lines were switched. The line set for the downstairs condensing unit was connected to the evap coil for the upstairs unit and vice versa.

I guess I never have really considered this, but it doesnt surprise me now that I think about it.

Anyone seen it before, and how do you check. Turn on the upstairs or downstairs system only and check the airhandler in the attic to make sure its correct and that the proper condensing unit is running?

In order for the units to turn on it would also mean that the t-stats were reversed as well.

Originally Posted by Scott Patterson

In order for the units to turn on it would also mean that the t-stats were reversed as well.

Not necessarily.

If both thermostats are in demand and turning on their perspective units, they could run, but would not cool properly.

Originally Posted by imported_John Smith

Anyone seen it before, and how do you check. Turn on the upstairs or downstairs system only and check the airhandler in the attic to make sure its correct and that the proper condensing unit is running?

Basically, yes.

Operate each system, see which a/c condenser unit is running, take the label information as usual, etc.

If both units are the same size, it would not matter. It would only matter if one unit is larger than the other and the small condenser unit is trying to satisfy the larger air handler.

I stumbled across this on a mid-rise where the first few floors had ground mounted condenser units and the top 5 floors had roof mounted condenser units. I simply could not get the condenser unit running for the 6th floor unit I was inspecting, then, while on the roof, scratching my head as to why not, it come on. I went back down to the unit and asked the buyer and agent if they had adjusted the thermostat in any way and they said no. I ended up writing it up for correction as needed.

The problem was discovered to be that when the units were removed from the roof two years earlier for re-roofing, they were connected back incorrectly - something like 80% were connected incorrectly. No one had complained as they all kept their thermostats set about the same, so all the units would come on, just not for the correct condo units.

Also had a project where 10 two story houses were connected reverse as you describe, we discovered it before anyone moved in and they were all re-connected properly.

Originally Posted by imported_John Smith

Anyone seen it before, and how do you check. Turn on the upstairs or downstairs system only and check the airhandler in the attic to make sure its correct and that the proper condensing unit is running?

I use the switch from cool to heat as the opportunity to check which unit is cooling what area. I occassionally find a duct connected to the wrong floor or wing.

I guess I can get more of an aerobic workout by switching on one unit, going outside and looking to see which condensor is running, then high tail it back into the hot attic to make sure the right air handler is functioning.

Im not sure why I never considered this could be an issue, after all, I have seen a few plumbing lines reversed in the past.

How many cases have you seen where the larger condensor unit was meant for the upstairs living areas? Please vote now.

Originally Posted by imported_John Smith

I guess I can get more of an aerobic workout by switching on one unit, going outside and looking to see which condensor is running, then high tail it back into the hot attic to make sure the right air handler is functioning.

Im not sure why I never considered this could be an issue, after all, I have seen a few plumbing lines reversed in the past.

How many cases have you seen where the larger condensor unit was meant for the upstairs living areas? Please vote now.

Very often the second floor has the higher load and therefore has the larger unit.

Doesn't make sense to me. If AC lines were hooked up to the wrong units, then I would think problems would have shown up that first summer. The main reason is without the blower, the evaporator coil would start freezing up in a short period of time. With as much ice that can form on the evaporator coil, if the blower did turn on or the condensing unit shuts off, it would take a long time (depending on the amount of ice built up plus other factors) for it to melt. During the melting process, the primary drain pan would not be able to collect that much water and so water leaking out of the evaporator box/plenum would have occurred. The secondary drain pan would clearly show that a problem or past problems existed. If there was no secondary pan installed (upright furnace in a basement for example), then there would be a lot of water (or water stains/rust) in the furnace and around the furnace.

Unless the blowers for both furnaces run 24/7 for air conditioning, I don't see how this improper installation could have gone un-noticed for so long.

I think Scott is right. The T-stats had to be wired to the wrong units also. If that happened, I would think the warmer apartment unit would keep turning their t-stats down while the colder apartment unit would keep turning their t-stats up. That would be funny.

Originally Posted by Kevin Luce

Doesn't make sense to me. If AC lines were hooked up to the wrong units, then I would think problems would have shown up that first summer. The main reason is without the blower, the evaporator coil would start freezing up in a short period of time.

I think Scott is right. The T-stats had to be wired to the wrong units also. If that happened, I would think the warmer apartment unit would keep turning their t-stats down while the colder apartment unit would keep turning their t-stats up. That would be funny.

Not if both apartments thermostats where set to the same approximate temperature. Then the thermostats would be calling for the units to cycle on at similar times, then along comes an inspector who, during testing, shuts one down for long periods and then turns it to heat ... that is when the entire Ponzi scheme unravels.

Originally Posted by Jerry Peck

Not if both apartments thermostats where set to the same approximate temperature. Then the thermostats would be calling for the units to cycle on at similar times, then along comes an inspector who, during testing, shuts one down for long periods and then turns it to heat ... that is when the entire Ponzi scheme unravels.

Even if both apartment thermostats were set to the same approximate temperature, there are too many factors that would result in the two units running at different times. Example: Second floor tenants having a birthday party that requires a lot of cooking while the first floor tenants are at that same party on the second floor. I can see that second floor needing a lot more cooling than the first floor due to the amount of people in that upper apartment and the cooking.

My original post was not an apartment, but a 2 story house. JP referenced some aparatments in his.

Originally Posted by imported_John Smith

My original post was not an apartment, but a 2 story house. JP referenced some aparatments in his.

Ok. Still the same conclusion. Heat rises so it is likely the upstairs unit will run more than the downstairs unit.

I think everyone know this but the size of the air conditioner mainly determines how well that unit will cool the house (or part of the house) during operation. Once the condensing unit turns off, then it is the design of the house (layout, insulated, how well it's sealed, etc), the temperature deference between the interior and exterior of the house and any internal items that generate heat that will determine when that air conditioner comes back on.

I did a inspection last winter when the furnace was running the temp was in the 70's the coldest furnace ive seen, as this was going on, waiting to see if it would wram up, checked the flame source in the attic, fine, as i was checkin windows , herd the A/C going, so a bad thermostat was to blame, and a high utility bill. at least i caught the problem, pulled the service disconect to the A/C so the client would have a nice warm winter

I did an inspection on a rooftop unit at a condo and found that thier unit had died so they just connected to the neighbors unit and used his.