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Going back to El Capitan, from H. Sierra...

dadders6

macrumors newbie
Original poster
Jul 15, 2019
4
0
Dallas
I have a mid 2011 iMac which was working fine, but slowing down a bit, so I preemptively had the HD replaced by an authorized Mac repair. He put High Sierra on it, but since then, the fans are blowing crazy (lots of folks are having this problem it seems) and I don't see any improvement over El Cap, since I only have 4 gig of RAM. If I completely wipe the drive (after backing up my files of course) will I then be able to download El Cap, which is still on the Apple store? Or do I have to somehow have a copy of El Cap handy (thumb sticks etc) to install it. - Thanks
 

mikehalloran

macrumors 68000
Oct 14, 2018
1,900
513
The Sillie Con Valley
Really? Sounds like an authorized person who didn’t know what he/she was doing — or you were presented some add-ones that aren’t really optional and you declined.

Was the OWC Temp sensor installed? If not, there are a number of crapware fan controllers — install one of them. The down side is that you must control the temp and fans. The other down side is that the fans will spin full till the extension loads every time you boot. If the installer replaced the HDD with another and tried to make the OE sensor work, it usually doesn’t.

If the temp sensor was installed, another connector was not plugged in correctly. There are three and any one could be the problem. On a 2011, the sensor is an inline wiring harness—if part of that harness was designed to plug into the logic board, it’s the wrong one (2009–2010).

Ok. 4GB is not enough RAM for High Sierra. There’s plenty on eBay cheap. Buy some.

Now as to your question. If you have a backup that precedes the High Sierra installation, you can wipe the drive and install El Cap, then restore. You’ll need a USB boot drive or other external to do the install. If your backup is from High Sierra, your only option is a clean install but that is only really time consuming, not impossible.

High Sierra runs really well on a 2011 iMac with an SSD. It can work on an HDD but it isn’t recommended. If it’s an HDD formatted APFS, that’s wrong with High Sierra as it was possible only during the beta period.
 
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Isamilis

macrumors 6502a
Apr 3, 2012
817
166
Have you try PRAM and SMC reset?. HS runs very smooth on mine. The GUI even smoother than El Capitan.
 
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Peter Franks

macrumors 68000
Jun 9, 2011
1,773
40
I put mine back from High Sierra, to just Sierra. Did you try that first, or only gone from El Cap to High Sierra?
May be worth a go?
 
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Amazing Iceman

macrumors 601
Nov 8, 2008
4,028
1,647
Florida, U.S.A.
Just upgrade the RAM all the way to 32 GB as I did with mine. It's under $100.00 at Crucial.com. Don't buy cheap but crappy RAM from other sources.

If the fans continue to spin like crazy after the PRAM and SMC Reset, it's most likely due to the new Hard Drive not being compatible with the hard Drive temperature sensor this iMac uses. Install SSD Fan Control to solve this problem, although your "Authorized Apple Tech" should know better to use the correct drive or install the OWC Temp Sensor mentioned above.

Going back to a version before High Sierra makes no sense, unless you plan on running old software.
 
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Mr_Brightside_@

macrumors 68040
Sep 23, 2005
3,417
1,535
Toronto
I have a mid 2011 iMac which was working fine, but slowing down a bit, so I preemptively had the HD replaced by an authorized Mac repair. He put High Sierra on it, but since then, the fans are blowing crazy (lots of folks are having this problem it seems) and I don't see any improvement over El Cap, since I only have 4 gig of RAM. If I completely wipe the drive (after backing up my files of course) will I then be able to download El Cap, which is still on the Apple store? Or do I have to somehow have a copy of El Cap handy (thumb sticks etc) to install it. - Thanks
You need it on USB unless your Mac shipped with El Cap. Downgrading won't fix the fans if he didn't install the temp sensor properly.
 
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