How to check refrigerant charge on a new AC unit
New HVAC installations often force guesswork with refrigerant weights due to missing manual subcooling targets and reused or buried line sets. This leaves people dealing with slow cooling and poor dehumidification while struggling to figure out whether the system is undercharged or overcharged.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
- 1Running the system at 100% capacity
- 2Using the check charge option through the thermostat to log data
- 3estimating line set length based on measurements
- 4adding charge until reaching a steady subcooling estimate
- 5relying on community or hands-on experience for target numbers when manuals lack details
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“Had a new full system installed a week ago and it doesn’t seem to be working as expected. I believe they undercharged the system.”source ↗
“I’m noticing less dehumidification than expected (marginally better than the system it replaced, which was bad at dehumidification). The cooling is also slower than expected. Takes nearly 2 hours to drop the house down one degree when it’s in the mid-80s outside”source ↗
“My line set is very long and buried in drywall so I reused it, and since the manual doesn’t list a subcooling target I relied on an estimate of the length to weigh in the charge.”source ↗
“Because now I don’t know how much was in there and it was late and I know it shouldn’t be 1.5, I added until I got about 5.0 subcooling steady.”source ↗
“My question is, how bad is it to be slightly over with a system like this, and since I’m a little unsure of the final weight, what subcooling is typical with this type of unit?”source ↗
Where this came up
People with this problem also raised
- 3Is vapor coming out of my apartment AC a refrigerant leak?
- 5Can you just refill a leaking HVAC system with refrigerant to get by?
- 5Are open cavity vent returns and exposed pipes normal in new construction?
- 2HVAC system stops taking refrigerant during charging
- 3Is water dripping from the car AC normal?
- 2How to get air bubbles out of the cooling system