Why is my AC running nonstop during the day in my new loft?

The short answer is your loft is acting like a giant greenhouse, and if the unit is acutally maintaining 74 degrees against afternoon sun trough single-pane glass, the system is likely working properly—it's just fighting an absurd solar load. Those unshaded factory windows are dumping thousands of BTUs into your concrete floor every single hour. Once that concrete absorbs thermal energy, it acts like a massive heat sink and slowly radiates it back into the room, wich is why the unit can't catch up til hours after the sun goes down. Before assuming the equipment is broken, install heavy **thermal blackout curtains**. You don't have to keep them drawn 24/7, but pulling them shut right before the sun hits around midday will stop that radiant heat before it ever enters the living space. If the building allows it, ceramic window tint is another massive help.

As for the noise, an empty room with polished concrete, bare drywall, and exposed sheet metal is basially an echo chamber. The blower noise has zero soft surfaces to absorb it, so the sound waves just bounce around endlessly. Throwing down large area rugs with thick felt pads, hanging dense drapes, and getting actual upholstered furniture in there will cut the reverberation down substantially. It won't silence the air moving through the ducts, but it stops the harsh resonance that makes it feel unbearable. To verify the mechanical side, grab an instant-read thermometer and check the **temperture split**. Measure the air going into the return grille versus the cold air coming straight out of the closest supply vent. You want to see roughly a 16 to 20 degree drop. If it's pulling in 74-degree air and blowing out 56-degree air, the AC is performing normally, and managing the solar gain is going to be your real solution.

Before writing it off purely as solar gain, have you ruled out the thermostat placement? If afternoon sunlight hits that wall directly, or if it's mounted on an uninsulated brick pillar that heat-soaks, the sensor is going to call for cooling non-stop even if the ambient air is fine. Also, for the roaring ducts—have you checked the air filter or ruled out excessive static pressure? If someone slapped a high-MERV filter in there or the blower tap is set too high for that duct diameter, the fan is going to scream trying to push the air thru.

Had the exact same issue in my old warehouse loft. What saved me was pre-cooling. I programmed the thermostat to pull the place down to 69 from 6 AM to 10 AM while the outdoor air was still cool, then let it bump back up to 74 at noon. Chilling that concrete floor early kept it from heat-soaking, and the unit actualy started cycling off during peak hours.

For the duct roar, check the hanger straps. Mine was vibrating directly against the ceiling anchors. Shoving some dense rubber isolation pads between the brackets and the pipe cut the low-frequency rattle in half.

What tonnage is stamped on the data plate outside? 1,600 sq ft with 14-foot loft ceilings is roughly 22,000 cubic feet—not standard residential volume. If that outdoor unit has a '036' (3-ton) in the model number instead of an '048' (4-ton) or '060' (5-ton), you're simply out of capacity against that afternoon glass load.

On the duct roar: have maintanence check the blower speed taps on the air handler board. Installers love setting ECM motors to max CFM (often 450+ CFM/ton) to 'push more cold air,' wich turns spiral ductwork into a jet engine. Dialing that back to 350-400 CFM per ton will kill the whistling and drop the noise floor drastically.

I'm super new to HVAC stuff, but does running non-stop for 6+ hours like that acutally damage the unit? I always thougt continuous running whould burn out the compressor, or is it actually worse for the system to constantly cycle on and off?

Also, probly a dumb question, but would ceiling fans help or hurt in a space that tall? I never know if running a fan just pushes down the hot air trapped near the roof and makes the AC work harder.

Quick update — the pre-cooling suggestion completely saved me! I started dropping the thermostat to 68 early in the morning before the sun hits, and letting that giant concrete slab chill early made all the difference. The AC actually cycles off during peak heat now. Also threw down a massive rug today and the deafening duct echo is finally gone. Thanks for the advice!