The condensation from my central air handler has been running through the secondary drain line and into the secondary drain pan (below the unit) for quite some time. My husband and I initially thought that the primary line was clogged, but this does not seem to be the case.
Here are pictures of our unit:
We had an HVAC technician come out to perform basic maintenance (including flushing out the drain lines) a month ago. He's convinced that we've got mold and mildew growing in our coil box and drain lines (and growing so fast that it's re-clogging them even two weeks after his visit). However, a certified mold inspector was adamant that this wasn't possible.
I don't think the primary line is clogged because you can feel strong airflow through the pour spout when you remove the cap (and you can hear it when the AC is on in a bathroom sink).
I opened the coil box yesterday, and there was some mold/mildew along the material above the evap coils, but none on the upper/outside portion of the coils (we have an A-frame with a plate blocking view of the inside portion of the coils and fins). I sprayed liberally with fungicide (rated for HVAC system use) and closed the box.
There's no trap on the primary line, the pour spout hasn't always been capped, and air escapes from the coil box around the panel and the front seam in the duct work immediately above the coil box (I've sealed this with foil tape for now and will add sealant later).
Given that the primary line doesn't seem to be clogged, the most likely (and frustrating) explanation seems to be that the unit wasn't installed well. You'll notice that the primary and secondary drain lines connect to the coil box at the same height, so someone would have had to add just the right slope to the unit or primary drain pan to keep condensation flowing through the primary line. As it is, I suspect that water flows freely through both at the same time.
I'd appreciate any help or insight. Thanks!