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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8670
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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The heating and cooling unit (in the attic) in is directly

Customer Question

The heating and cooling unit (in the attic) in is directly above the master-bed room. When the air conditioning unit cuts on, there is a constant drip drip noise, then that noise will stop. I have searched around the unit to look for water, but there in
none. Do you have any insight to what is causing the dripping noise.
Submitted: 2 years ago.
Category: HVAC
Expert:  Phil replied 2 years ago.
Hello, the most likely cause, is that condensate drain directly under the cooling coil is clogged and over flowing to the much larger and out in the open emergency drain pan under the entire unit. 98% chance of that. There is a much less likely chance that the condensate drain line is piped so that water flow from the pan falls into the condensate trap, making a drip sound...2% chance of that. Any water leaking into the attic will support mold and dry rot, that can damage or even ruin the property if too much mold develops... inspect for that carefully.-------We are on the honor system here. Please remember to rate my service before you leave today. If you need anything else, just let me know. You can continue asking follow-up questions within your agreed on limit at no additional charge.
Customer: replied 2 years ago.
There is no condensation in the pan underneath the cooling unit. I have looked for leaking pipes and found none. No mold and no dry rot. I had done all this before, but I checked again. In the past, when the unit cuts on, I go to the attic, (it's a walk up, floored attic) and inspect the running cooling unit, and no drips. I have already checked for what you have suggested. The reason I asked, was I thought someone elase may have experienced this mystery sound.
Expert:  Phil replied 2 years ago.
Hello again, this is the very first time I have heard of such a dripping sound, combined with no visible water leak or puddle in my 51 years, and many thousands of jobs.
Tell me please where the condensate line terminates please. If it runs to sewer vent stack, you would get a dripping sound as the water falls to the bottom of the stack. (that would also be an illegal and unsafe installation as sewer gas will get sucked into the HVAC system in heating mode when the condensate trap is dry)
It you do not have that situation, I will opt out so others here can look your situation over.
Customer: replied 2 years ago.
The condensation pipe runs in front of the unit for about 10 feet ( I am gusessing) makes a right turn to the edge of the house, also about ten feet, then heads down the inside wall about 20 feet or more ( we have a three storey home, with a 12 degree pitch roof) and terminates in a puddle outside the foundation ( another problem I am working on).I thought it might be dripping as the air handler unit turns on (an air leak), it pushes any condensation in the trap out to the down spout pipe and that gives a rapid drip drip sound as the condensation is pushed out.Has any one askied you about a dripping noise before?
Expert:  Phil replied 2 years ago.
Thanks, ***** ***** that the condensate line terminates outside. This is the first I have heard of a dripping noise in the field for 51 years or on line here for 5 years.... that has been across thousands of jobs. The dripping noise is unusual to say the least.The odds that anyone else has heard or it is slight if my experience is any indication. Your comment that air pressure is pushing the water accumulated in the condensate out of the trap is the key to solving this issue. The air side of the cooling coil runs between 0.3 and 0.5" of water column by design, and by blower design limits *unless you have a variable speed ECM type blower motor... in that case the pressure can be a little higher. Most condensate traps are 2 to 4 inches preclude this problem. Tell me how deep your condensate trap is, and if it is a P shaped trap. or a shallow curve shaped trap. We can go from there.