Any help appreciated here. Working in a cramped attic space in the heat troubleshooting this has worn me out and I’m out of ideas.
Home has three units, all working.
Problem - Secondary A/C drain is active indicating plugged primary drain.
Secondary drain pans on unit 1 and unit 2 are dry, indicating their primary drains are working.
Secondary drain on unit 3 is full and actively draining out the soffit vent of the home.
All three primary drains are plumbed together to a totally plugged drain to the sewer line. This line has a standing column of water all the way up into the attic. I have applied 60 PSI air to the common drain line to the sewer and it won’t blow out.
Turns out that unit 1 and unit 2 primary drains have thus been flowing retrograde into the condenser pan of unit 3, activating its overflow into the secondary drain.
Units 1 and 2 run together:
After this junction I added a valve so I could create pressure distal to the valve for blowout:
Fortunately the third unit was just slip fit and not glued into this junction, where I unsuccessfully 60 PSI applied air pressure to blow out the plugged line:
Unit 3 cut line for troubleshooting:
Secondary drain pan of Unit 3 is full and draining through the secondary line:
The plugged line is a 3/4" PVC line that runs down an internal wall in the home, presumably into the sewer line. I have not been down there to see how it connects. That wall is shared with a bathroom but the sinks are on the opposite wall although there is a tub and shower near by that wall. Both are draining properly.
Thoughts on the next step? Can that 3/4" line be snaked with a cleanout device? Extremely tight quarters in there
A prior HVAC guy did a blowout of some sort a couple of years ago and said he things he lost part of his blowout gun into one of the lines. Perhaps a rubber tip of some sort?? Don’t know if this is lodged somewhere.
Not sure how to proceed. I’d settle for just running a primary drain somehow to another soffit and just let it drip but the roof is very low pitch and a real pain to work in. Having all three units backing up through the condenser unit 3 primary pan is a disaster waiting to happen.
I described the problem to one HVAC guy and he did not want to work on it. My original guy was great but passed away