Why does my brand new AC not cool as well as the old one?
New cooling systems often feel less effective because installers may misconfigure airflow settings or fail to balance multi-room temperatures properly. This leaves homeowners dealing with rooms that stay significantly warmer than they were with older equipment, causing regret and doubt over the replacement choice.
What the numbers show
Counted from the threads quoted below. How we count
- Most of it landed at once — the busiest month was September 2026, with 14 people.
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.
- 1Using blackout curtains2 people mentionedDid this help you?
- 2Contacting the installer to adjust the fan speed and refrigerant chargeDid this help you?
- 3Buying ecobee sensors and a digital thermostat to check for equipment discrepanciesDid this help you?
- 4Dropping the desired temperature setting to force the units to run harderDid this help you?
- 5Digging through thermostat logs and researching fault codes independentlyDid this help you?
- 6Flipping the air filter directionDid this help you?
- 7Checking breakers and outside unit componentsDid this help you?
- 8installing full-house dehumidifiersDid this help you?
- 9hiring multiple HVAC companiesDid this help you?
- 10adding portable dehumidifiersDid this help you?
- 11getting an energy auditDid this help you?
- 12using a temporary window unitDid this help you?
- 13Replaced the reversing valveDid this help you?
- 14Replaced the liquid line filter drierDid this help you?
- 15Disconnecting the reversing valve from the motherboardDid this help you?
- 16Sealing gaps and cracks in the door and floorDid this help you?
- 17Switching from a single-hose to a dual-hose portable unit or a window unitDid this help you?
- 18Waiting for the installation technicians to return and finish servicing the systemDid this help you?
- 19cover skylights with tarpsDid this help you?
- 20installing window tintDid this help you?
- 21installing ceiling fansDid this help you?
- 22adding more AC unitsDid this help you?
- 23having a technician check the exact model numbersDid this help you?
- 24inspecting the electrical breakerDid this help you?
- 25shutting the system down completely and leaving it off overnightDid this help you?
- 26opening all supply vents fullyDid this help you?
- 27calling an HVAC technicianDid this help you?
- 28Replacing the capacitor independently based on online instructions after discharging safety energy.Did this help you?
- 29Turning the system off for about 30 minutes and restarting itDid this help you?
- 30Waiting for the original installer to return and check the systemDid this help you?
- 31changing filtersDid this help you?
- 32cleaning the A frame and condenserDid this help you?
- 33checking drains and refrigerant levelsDid this help you?
- 34calling another company or seeking a second opinionDid this help you?
- 35searching online for troubleshooting possibilitiesDid this help you?
- 36waiting for the contractor to returnDid this help you?
- 37Running a separate standalone dehumidifierDid this help you?
- 38Setting the thermostat a few degrees lower than the previous comfortable settingDid this help you?
- 39Waiting 24 to 48 hours for the system to cycle and remove humidityDid this help you?
- 40buying a dehumidifierDid this help you?
- 41adjusting blower fan speedDid this help you?
- 42checking thermostat staging configurationDid this help you?
- 43Check the outdoor unit to see if it is frozenDid this help you?
- 44Turn the unit completely off to let it defrostDid this help you?
- 45Call an AC technician for repairsDid this help you?
- 46Check if air is actually flowing from the ventsDid 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.
“So I have two mini split units, senville brand both 12,000 btu. It’s 95 degrees right now and my house is 85 degrees upstairs and 80 degrees downstairs. I genuinely don’t know what to do.”source ↗
“For context-I live in Houston area, so it’s hot and very humid 6+ months out of the year. So; back in April my AC was set at 70 degrees but wouldn’t get below 78/80 degrees all hours of the day and humidity in our house was reaching almost 70%.”source ↗
“At this point we’ve spent upwards of $9K on our AC system and it is set at 70 degrees and can’t get below 75 degrees—>even overnight when it’s 77 degrees OUTSIDE. And our humidity is still high as well….completely at a loss of what else it could be and just looking for suggestions on what to do”source ↗
“The new system does blow a little cool air, but doesn’t cool the house at all on a sunny day.”source ↗
“This system is the same or worse than what I had previously. Obviously, I am $45k poorer and still hot.”source ↗
“Are they required to make it work if their bid or their work was wrong?”source ↗
“I got 2 new Carrier Infinity units last week and so far I've been underwhelmed.”source ↗
“We also now have a room that is significantly warmer upstairs than before.”source ↗
“yesterday it suddenly stopped cooling properly and the airflow from the vents became weak.”source ↗
“After running in COOL for about 15 minutes, it’s still barely cooling.”source ↗
“So I’m only getting about a 3.2°F temperature drop.”source ↗
“The unit fails to cool and is about 6°-8°F high of set temperature.”source ↗
“The unit runs near constantly but fails to ever reach set temperatures until later at night when the outside temperature cools off.”source ↗
“I noticed now, approx 4 hours later, that it’s blowing about 65 at that same vent and it’s 76 in here.”source ↗
“after spending so much $ I have some anxiety about it.”source ↗
“We are having issues with the ac not cooling our apartment.”source ↗
“Its been on for hours but its gone from 75 to 77”source ↗
“the next day my wife said she felt the new system didn’t cool as well as our 15 year old carrier did.”source ↗
“So I’m left now trying to figure out what’s going on and hoping we didn’t make a mistake going with the installer and unit we went with.”source ↗
“Reaching desired temp for the house. Which our old units could do. One room warmer than it was on the old units.”source ↗
“its not blowing cool air.”source ↗
“The installer is stumped, the company i bought it from is refusing to offer any help”source ↗
“Im at my wits end here. Ive been struggling with these companies since August 11th.”source ↗
“for whatever reason it doesn’t seem to be doing a good job at keeping my little shed cold.”source ↗
“After being on for about a half hour, the room read 77 while the air coming from the unit measured 66.”source ↗
“There is a very small leak coming from my door too which i do plan to seal up but could that make a major difference?”source ↗
“That 18-19F split just tells you it’s cooling right now. It doesn’t really prove the setup is correct.”source ↗
“The R22 only - label on a 1996 coil paired with an R410A condenser would definitely make me question what was actually done back then.”source ↗
“And yeah, if the condenser says 40A max and it’s actually on a 50A breaker, I’d get that looked at too.”source ↗
“Fast forward to September 29, the blower is blowing, I can hear it blowing strong, I changed the filter, but its not cooling smh.”source ↗
“What could it be now???”source ↗
“It worked perfectly and blew cold air for about 2 hours, but then it suddenly started blowing room-temperature air.”source ↗
“The outdoor fan is running, but the compressor doesn’t seem to be running.”source ↗
“The outdoor unit came back on after a short delay, but it still isn’t cooling.”source ↗
“Charge me 60 bucks to say my unit is at capacity and running fine”source ↗
“Got a new unit installed - day of install the condo is still hot. I called the company and they said the temp which was showing 74 at the time then that’s the temp.”source ↗
“The new unit won’t go below 60 - the sales guy said 65-60 is ideal humidity, but when the tech came earlier in the day he said it was hot too.”source ↗
“Literally in tears bc the old unit was so nice and just dropped 11k on this and customer service is terrible.”source ↗
“I used to wear a sweater in the house at 74, it’s mildly hot and uncomfortable rn. I feel cool air but I’ll give it more time I guess - what do I do if nothing changes the sales guy is being quit hard, but the tech told me it’s hot.”source ↗
“It is. Kinda. Its not nearly as cold as it was.”source ↗
“My wife replaced the hvac filter inside i think a week ago?? and lately the house has not been cooling down.”source ↗
“Today it got up to 80 in the house.”source ↗
“The A/C is running but its just hot and idk what to do because its confusing.”source ↗
“Then it all went bad, BOTH mini splits stopped throwing cold air and both rooms became so so hot. I am so confused on what happened... he comes back tomorrow later in the day. which sucks bc i've spent all week dealing with this project. please help.”source ↗
Where this came up
People with this problem also raised
- 31Refrigerator and freezer stopped cooling completely with loud humming noise
- 4HVAC contractor installed mismatched heating and cooling parts
- 3Refrigerator stops cooling properly after being moved on its side
- 4Thermostat doesn't work after opening it up
- 6New HVAC unit won't heat and makes clicking sounds
- 25Why is one bedroom getting way more air than other rooms?