A/C Window unit question

I have a small shop that I work out of, and it is really, really hot in there this Texas summer. It is a 20x22 single garage-style unit, with insulation in the walls behind light paneling, but no insulation in the rafters anymore. The building is surrounded by trees, but the sun beats down on the roof all day, and the south door gets sun on it all afternoon.

I have a 11,500 BTU 110AC window unit air conditioner mounted in the north wall. I can start it up at 8am, and let it run all day, but by 1-2pm, you better be in front of a fan if you want any relief from the heat. By 3-4pm, it can barely keep them temp down to 95 degrees.

Now, it gets so hot by late afternoon, that the compressor on the A/C kicks off and the unit will not cool or cycle.

I used to have an old 1970s unit in the same place, and it basically had an ON/OFF switch, so it would run, even if it couldn’t cool the place down. The current A/C (only about a 4 year old model) decides if it will cycle or not, so it justs blows hot air when it’s really hot.

Does this newer unit have some kind of limiter on it? Is the thermal load just too much for it? I don’t expect my shop to be nippy on a hot Texas day, but 11,500 BTUs for 440 sq/ft should make it bearable, right?

Then again, the central A/C is my house is running all day and it barely keeps the inside at 84 degrees during the day.

Yeah, it’s possible that the compressor has a thermal cutout. Without insulation in the overhead, there’s no way that AC is going to keep up. It’s basically cooling the air about a foot in front of it as the roof radiates molten lava into the space.

Pretty much has an overload protector the other doesn’t. Guess the older one risked its life and yours whenever it kept cooling when it shouldn’t have!
Can you add insulation or anything to separate the space above? Insulation is vastly under-rated.

How about a ceiling of insulation boards?


I agree with the previous comments about the window unit. Your central a/c unit sounds like it’s either undersized, not performing properly or perhaps the dwelling is not adequately insulated.

If there is a possibility of painting the roof white - it can help.

Does notsoundllike the unit is working properly. Sounds like it is dieing.

Why is there no insulation in the rafters? Do you have a ceiling and attic space? Or is the ceiling the underside of the roof?

Look into installing a radiant barrier on the underside of the roof. You know how it feels cooler in the shade than in the sun? That’s because the tree is blocking the radiant heat. The air is still the same temp in the shade, but you’re not being bombarded with radiant heat. A radiant barrier on the roof will reflect that heat back outside.

If you have a garage door, insulate it to keep a lot of heat out of the space. Seal up any cracks so that the cool air stays inside. Block windows with that foam insulation where one side has a radiant barrier and have the radiant barrier facing the glass.

A 11,500 BTU AC should be able to cool that space as long as it’s well insulated. You should be able to fix up your shed so that it stays cooler.

FYI-- If you add a radiant barrier, make sure the radiant foil side is facing open space. You don’t want the foil to be in contact with a surface or else it will conduct the heat.

Thanks for all the replies.

I once had insulation in between the rafters of the roof, but it fell down over the years and I removed it. I really need to install new insulation in the roof and put a false ceiling in to seal off the upper area from the lower eight feet so that I have a smaller, cooler area to cool down.

“Pretty much has an overload protector the other doesn’t. Guess the older one risked its life and yours whenever it kept cooling when it shouldn’t have!”
Was there a danger in running the old unit this way? I did it for many years with no problem.

Probably only to the compressor. I’m surprised it didn’t burn out.

Whenever you decide to insulate and enclose that rafter area, you might consider installing a thermostatically-controlled exhaust fan up there on one of the gable ends. It will help reduce the cooling load on your window shaker.

No the unit shuld be able to run with both high inside andoutside temperatures. But an overloaded AC unit will have its life shortened. Normally they just die, no fire.