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Old 06-09-2021, 03:59 PM
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Default House AC Temp

Not sure my house AC is cooling enough. What should the temp be at the vent?

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Old 06-09-2021, 05:32 PM
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Timely. Being in the 90ís all week my central air seems to struggle. I pressure washed the outside unit, changed the filter,unblocked any covered vents,close curtains in sunny windows,ect. . Was thinking on calling my HVAC guy just to have him check it out. Itís been this way for the couple years Iíve lived here.

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Old 06-09-2021, 10:58 PM
GtoFM GtoFM is offline
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A/C is designed for indoor temps 15* lower than outdoor temps. So if it's 90* outside and your house is 75*, you're doing good. Humidity control is key. A/C may run 10 times per hour to control humidity. You may be comfortable at 78*/40%RH but miserable at 72*/60%RH. The air coming out of the registers should be 15-20* lower than the temperature at your thermostat.

The outdoor unit may need washed, but be careful not to flatten the fins, that will compound the problem. And, yes ck/change the filter.

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Old 06-11-2021, 11:14 AM
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Originally Posted by GtoFM View Post
A/C is designed for indoor temps 15* lower than outdoor temps. So if it's 90* outside and your house is 75*, you're doing good. Humidity control is key. A/C may run 10 times per hour to control humidity. You may be comfortable at 78*/40%RH but miserable at 72*/60%RH. The air coming out of the registers should be 15-20* lower than the temperature at your thermostat.

The outdoor unit may need washed, but be careful not to flatten the fins, that will compound the problem. And, yes ck/change the filter.
I'm pretty close to those numbers. Had the "AC" man come out yesterday and top off the system, it didn't take much. Register temp dropped 1-2 degrees.
My unit is 26 years old with obsolete/discontinued freon. He had some.
I timed it, 10-12 minutes on. 10-12 minutes off. 88 outside.
91 today. Stay cool.

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Old 06-11-2021, 11:20 AM
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My problem is mine runs continuously when itís this hot. 93 yesterday, supposed to be 95 today.
I texted my HVAC guy yesterday, but havenít heard back yet.

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Old 06-11-2021, 06:22 PM
jerry455 jerry455 is offline
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It is just under 90* here north of Detroit. My A/C system was installed in 1984 and has been topped off by my buddy about 10 years ago. I have had to change out the cooling fan motor and the capacitor for the condenser outside. Have had good luck with my old inefficient system. The A/C companies always try to sell me a new system because mine is so old. It still works and works well. My wife likes it cold. My dog and I like to go out and warm up. The temps have been coming out of the vent around 20* colder than outside. We had our house insulation beefed up a couple of years ago and that has made a big difference. My upstairs bedrooms were always warm in the summer. We had more insulation put in and it has made a big difference.

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Old 06-14-2021, 09:41 PM
John V. John V. is offline
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When I lived in Fla, I kept an analog thermometer pierced into the return box just ahead of the filter and another just after the evap coil. I would get about an 18 F differential which HVAC techs told me was what I should expect. I kept them in place so that whenever I suspected an issue, the temp differential provided the data.

Original heat pump (basically an AC unit with a reversing valve to provide heat in winter) was from 1994. I replaced it around 2007 with a much more efficient (at the time) unit. After seeing a substantial reduction in my electric bill, I realized I was stupid for limping along with a failing unit that needed freon every several months that was getting expensive (old freon) at the time.

That unit failed around 2018 just after the 10 year warranty expired (partly my fault because it actually had started acting up a year earlier but I ignored it because I forgot I had the 10 year warranty).

The 2018 unit was even higher efficiency but the utility savings were not noticeable as the percent increase in efficiency was not nearly as big as it had been in 2007.

Moral of the story, if your unit is pre-2000 and you use the AC a lot, you may find that the payback on a new unit is relatively short based on electric savings. Up north might not be as dramatic as your AC will run less often. In the '80s and '90s, living in the Chicago 'burbs, we rarely turned the AC on.

Here in the mountains now, my original to this house 1999 unit is still running fine and since we haven't yet had to run it this season, hard to justify a replacement although my plan is to replace it with a heat pump as I believe it may be cheaper for electric to run it for heat above 35 F ambient than my high efficiency condensing furnace that runs on propane at roughly $2/gal. I would run it as a "dual fuel" system to manage my utility costs to best advantage.

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Old 06-16-2021, 08:22 PM
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Quote:
Originally Posted by John V. View Post
Moral of the story, if your unit is pre-2000 and you use the AC a lot, you may find that the payback on a new unit is relatively short based on electric savings. Up north might not be as dramatic as your AC will run less often.
This is 100% true, especially if you have a variable speed compressor and fan (rather than the old traditional 1 or 2 stage compressors) which allows it to run more and more efficiently and use less power to keep the house regulated.

I put a multi stage compressor system in my house and my electric bill (E. TN) dropped $150-175/mo in the spring and summer months AND the house was cooler and drier.

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Old 06-27-2021, 04:28 PM
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63 deg coming from my vent.

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Old 06-27-2021, 06:59 PM
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Mine was 2.5 lbs. low on Freon. Should be a lot better now I would think, but it cooled off the day my HVAC guy got here. So the real test will be when it gets back in the 90ís.

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Old 06-28-2021, 06:50 PM
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Quote:
Originally Posted by John V. View Post
...I would get about an 18 F differential which HVAC techs told me was what I should expect...
Yep. Just like our car AC units (or for that matter our car radiators), what matters is the temperature difference between the temperature going in before the coils and the temp coming out.

Right now it's 102 outside here and the house thermostat has been set at 77į since early this morning. I just shot the temp gun at the nearest vent to the AC system and it was 60.5į. So things are working pretty good with about a 16į cooling difference. Unit also cycles off fairly often which gives the AC coils enough time to de-ice and not turn into a block of ice.

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