Mold on Coils

Good day, we have recently had a new HVAC system installed - the whole kit and caboodle - a little under 2 years ago. Our home is 1900 sq. ft. and we were having problems with a 3 ton unit cooling our home. They put a new return in our living room for a total of 3 returns and it still didn’t help. They took that unit out and then plopped in a 4 ton unit. It sure does keep it cool but now we are growing mold on the coils. We were quoted $1600 for a media filtration system and UV light or $300 to clean the coils. I believe this is their error. When installing the unit (keep in mind it took them 6 months just to get that right) they should have mentioned something then. They stated that because our unit is electric it just doesn’t have enough space to cool and dry the air, therefore, creating mold. We have a limited lifetime warranty so we can’t get a second opinion or BOOM! voided warranty. After spending $6000 for a new unit and another $1600 for a new return I am feeling fed up and seeking advice here.
What is the cause of mold? We never had mold on our old unit of 17 years. We live in Houston, Texas so humidity is very high.

I would call the manufacture of the unit, I can not see why it would void the warranty if it is a authorized dealer . sounds like they are ringing the cash register when you call them


The air conditioner may be too big now. The longer the air conditioner runs the more humidity it takes out of the air. Your old unit had to run longer to try and reach the temperature you set, which reduced the indoor humidity. The 4 ton unit may be too big, which cools the house down too quickly leaving more humidity in the air and on the evaporator coil. Mold needs two things to grow in your AC unit. One is moisture which is provided in the form of condensation on the evaporator coil and a food source typically dirt or dust on the coils. If you use cheap air filters or the plastic screen that comes on most new air conditioner units too much dirt is passing through the filter onto the evaporator coil. No one can diagnose you problem over the internet. The ideal situation would be to get a professional HVAC contractor to properly size the unit and possibly add a humidistat and don’t forget to use good air filters.