HVAC system stops taking refrigerant during charging
Retrofitted or low-pressure systems often stop pulling in refrigerant prematurely while running, leaving the unit undercharged and freezing up the expansion valve. This happens when suction pressure drops too low to keep the compressor running or allow the remaining charge to enter the system.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
- 1charging through the low side while the unit is running
- 2verifying line and tank connections for blockages
- 3clearing and pulling a fresh vacuum before recharging
- 4turning off the breaker for 10 minutes
In their words
Unedited, most upvoted first, each linked to the thread it came from.
“Attempted to convert a r22 3.5ton Lennox system to 422b, unit takes some charge but it stops taking it and when running unit freezes txv because of under charge but still won’t take it in.”source ↗
“New tank on my scale it only took 2lbs then i sat there for 10 mins running the unit it just wouldn’t take it”source ↗
“Obviously there is low r32. That's why we're trying to add more. But how tf can we when it won't run the compressor?”source ↗
Where this came up
People with this problem also raised
- 4Can you just refill a leaking HVAC system with refrigerant to get by?
- 4Why does my new ice maker only fill with water once?
- 9Why do cooling coils keep freezing over?
- 12Refrigerator and freezer stopped cooling completely with loud humming noise
- 2AC unit humming with no air coming out of vents
- 10Why does my brand new AC not cool as well as the old one?