Cool air leaking from gap around AC copper pipe in attic
An unsealed gap where the copper refrigerant line enters an attic AC unit allows conditioned air to escape, creating a noticeable cool breeze in a hot space. Homeowners frequently discover this opening while changing filters and wonder whether it indicates a system malfunction or a harmless non-issue.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1throwing some foil tape on it to block airflowDid this help you?
- 2sealing that gap with something called Plumber's putty or Thumb-gumDid this help you?
- 3using cork tape to seal itDid this help you?
- 4Changed the seal on the vacuum gaugeDid this help you?
- 5Pressure tested fittings, gauges, and core removerDid this help you?
- 6Sprayed everything with bubblesDid this help you?
- 7Bypassed the manifold completely and went directly from the unit to the vacuum pumpDid this help you?
- 8Put the system back under nitrogen to check for pressure loss over a few daysDid this help you?
- 9Using foil tapeDid this help you?
- 10Using gorilla tapeDid this help you?
- 11Using mastic tapeDid this help you?
- 12Using a home warranty for an HVAC inspectionDid this help you?
- 13Place a PVC cap on the cleanout tee without gluing it.Did this help you?
- 14Fill the penetration hole with silicone or mortar mix.Did this help you?
- 15Install a P-trap on the condensate line to keep conditioned air inside the system.Did this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“We bought this house and moved in about a year ago. Today my husband was in the attic to change the air filters (two AC units) and he noticed a gap where this copper pipe is going into one of the units.”source ↗
“He tried sticking his finger near/ into the gap and felt a light cool breeze coming out (it's pretty hot in the attic, so easy to tell that there's a cool breeze coming out).”source ↗
“It just seems odd so we're curious if this is something that should be checked out or a non-issue.”source ↗
“On my last few AC installs, my vacuum seems to hit a wall at around 650–700 microns.”source ↗
“Today I pulled a system down and the lowest I could get was about 660 microns.”source ↗
“I isolated the vacuum pump and watched the micron gauge. It rose from roughly 660 to around 800 microns, but then stabilised and held around than continuied to creep up.”source ↗
“I keep getting stuck around the same 650–700 micron range, which is making me think it might be something in my evacuation setup rather than every system having the same issue.”source ↗
“I’m closing on a house and the inspection report stated something about the ac condensation line having “excess amount of cold air coming out of condensation line”.”source ↗
“My question is, is cold air coming out of the condensation line something i need to address ASAP?”source ↗
“air blowing out of the, according to google, supply plenum. It is enough that the closet it is sitting in stays cold while the rest of the house struggles to cool.”source ↗
Where this came up
People with this problem also raised
- 2How to get air bubbles out of the cooling system
- 5Can you just refill a leaking HVAC system with refrigerant to get by?
- 12Is my outside unit leaking oil or condensation?
- 6How to get trapped air out of a car cooling system
- 9Water spitting out of pump vent pipe
- 3Why is cold air blowing out of my AC drain line?