Installed carrier infinity system (removed old hot water system; put in all new ductwork and carrier equipment) in reno/addition project (own home) late summer 2009.  Fantastic--at first.  When I turned on ac following season, terrible odor filled house, mainly 2nd floor.  Installer came out, recharged one unit.  Odor persisted.  Installer could find no problems, suggested contacting carrier directly.  Unimpressive result.  Carrier told me to work with another contractor, but no help or suggestions offered.  Problem worsened to the point that odor was triggering asthma in sensitive individuals in house.  Original installer came back out.  Still no help.  Told me to hire an industrial hygienist.  So bad at end of 2010 season, I had to turn off the ac altogether.  Mild to no odor during heating season (though this is variable).  Dreading the start of new coolong season.  Anyone have any thoughts?

Does the odor smell like dirty socks

Check the condensate drain, make sure it is clean and allowing water to flow away. Make sure it is not connected to a sewer line and allowing gases back into the system. Make sure there is a trap on the condensate line. Make sure your cold air returns and filters are not restricted or blocked. This could cause a negative pressure or vacuum in the air handling unit, allowing sewer/septic /drain odours to be pulled into the unit. Check the ac coil is clean. Is there a fresh air intake on the unit, if so make sure it is not located near a toilet "stink" pipe. Hope this helps.

Dirty sock syndrome is quite common. Microrganisms grow on the evaporator coil and the only way to prevent this from reoccurring is first make sure water drains from condensation pan, chemically clean coil and have coil coated. Improve air filtration, seal ductwork and dehumidify air to 40-50% relative humidity.

One more- If you have a humifier located downstream from your filter (rare and not typical), check that water drain is properly trapped so vapors can not be sucked up from the drain or condensate pump. This can be a source for mold to get started on the coil, etc.

A UV light can be added to the coil area to kill growth, but all plastic and wires has to be protected or be UV safe.

Posted By insulateright on 21 Mar 2011 07:17 PM 
Make sure it is not connected to a sewer line and allowing gases back into the system.

It is not allowed in many places, but Louisiana encourages this practice