If you turn off the first floor AC, does the lilac smell migrate to the first floor from your cellar table?

If not, you are right and the installer is wrong. You have a duct leak somewhere that is drawing cellar air into your system. That depressurizes the cellar and pressurizes the first floor. Outside air is then sucked into the cellar and inside air blown out of the first floor area. That seems like way too much air leakage for a new system. It is inefficient at best, but it can cause other problems as well.

Depressurizing an area of the home can be dangerous. It can prevent the exit of combustion fumes from water heaters, boilers and furnaces and fill the house with them. What kind of heat and water heater do you have and where are they located?

If you cellar is cool and outside is humid, drawing in outside air could lead to higher humidity in the cellar if the dew point of the outside air is lower than cellar temperature.

f the system is not supposed to condition the cellar, you should not see much of an effect on humidity down there. What was the cellar humidity like before AC install? You might have to attack this problem separately. Is it warm or cool down there?

Did the same outfit install the second system?

Thanks Ionized.

If I turn off the A/C, I get no smells from the basement. No damp/musty smell and no lilac smell.

I have a tankless water heater and an oil tank for oil heat, both in the basement.

When the installer came to check the problem, he told me that the A/C was supposed to help dry out the basement. The basement is a little cooler than the first floor.

The humidity seems worse than before I installed the A/C. I thought that I might be because I power-washed the basement floor a month ago and the damp spots have not dried even though I ran two portable de-humidifiers for several days afterwards. (There is a french drain around the perimeter that channels water to an exit point out of the house.)

The installer installed both systems. The upstairs system works fine and there are no unusual smells.

The installer is making no sense if you are relaying the information correctly. If the AC is supposed to be helping to dry the basement, you will get air mixed into the first floor air. Yet he checks for leaks in the cellar ducts. Small leaks would be of little importance if there are intentional ducts openings there to intentionally circulate drying air.

It sounds like you have a moisture problem in the cellar that should be addressed. If hot, humid air from outside is being drawn in by your new AC, it cold be making the humidity problem worse.

Can you check to see if air is being drawn in through the water heater or chimney when the AC blower is running?

Make sure your condensation line has a trap in it. I don't know where you are draining it to but if it is draining to a basement drain, if there is no trap it could pull air from the basement into the system

Ionized--

I understand. Now then, I don't see how the basement could get dry if there are no openings in the ductwork in the basement. I will ask the installer to clarify.

I will check tonight to see if air is being drawn in through the water heater or chimney when the A/C blower is running.

Busboy--
My condensate line is a small pvc pipe that drains into an open French drain in one corner of the basement. I do not know if there is a trap. But that is certainly something to check, especially since the pipe ends at the most damp and odorous corner of the basement.

The drain should be positive, shouldn't it?

I checked for a trap. There is a j-shaped pipe leading out of the condenser unit and the drain is directed positive (downhill) until it gets to the floor, then it is flat until it gets to the drain opening in the floor, when it is positive again.

I ran the A/C with a lighted incense stick at the end of the drain pipe and the smoke from the incense stick did not get drawn into the drain pipe.

I did find that there is a section of bellows-like material that is stapled closed and air might be getting in there. I also found that when I placed the incense stick at the top of the condenser unit, the smoke blew around alot and I could feel an air current

This thread is from 2011. It EXACTLY describes to a tee my situation. Wondering, if Lynnie338 is still on GW, if there was a resolution?

I'm desperate!

My situation as well. I have cat litter boxes in the basement and the smell is pulled to first floor. Will now undertake sealing the returns.