Replace the hard drive in your iMac Intel 21.5".

This guide also includes steps to upgrade your iMac's hard drive with a SSD. It describes how to install the SSD's temperature sensor so that the Mac's fans will operate at the correct speed.

Before beginning any work on your iMac: Unplug the computer and press and hold the power button for ten seconds to discharge the power supply's capacitors.

Be very careful not to touch the capacitor leads or any exposed solder joints on the back of the power supply.

    • Before beginning, unplug your iMac and lay it on a soft surface as shown.

    • Stick a suction cup near each of the two top corners of the glass panel.

    • To attach the suction cups we sell, first position the suction cup with the movable handle parallel to the face of the glass panel. While lightly holding the suction cup against the glass, raise the movable handle until it is parallel with the other handle.

    • If your suction cups refuse to stick, try cleaning both the glass panel and the suction cup with a mild solvent.

  1. Gently lift the glass panel perpendicular to the face of the LCD enough to clear the steel mounting pins attached along the underside of the top edge of the glass panel.
    • Gently lift the glass panel perpendicular to the face of the LCD enough to clear the steel mounting pins attached along the underside of the top edge of the glass panel.

    • Pull the glass panel away from the lower edge of the iMac and carefully set it aside.

    • During reinstallation, be sure to meticulously clean the inside of the glass panel and the face of the LCD as any dust or fingerprints trapped inside will be annoyingly visible when the machine is turned on.

    • Remove the eight 8 mm T10 Torx screws securing the display to the outer case.

    • The last two pictures are detail shots of each side of the display.

    • Slightly lift the top edge of the display out of the outer case.

    • Do not lift it too much. There are several cables attaching the display to the logic board.

    • Pull the vertical sync ribbon cable out of its socket on the LED driver board near the top left corner of your iMac.

    • The vertical sync ribbon cable has a ZIF style end, but the socket has no lock or retaining flap. Simply pull the cable away from its socket toward the optical drive side of the iMac to disconnect it from the LED driver board.

    • Rotate the display out of the outer case enough to disconnect the LED backlight power cable from the LED driver board.

    • Disconnect the LED backlight power cable by depressing the locking mechanism while pulling the connector away from its socket (toward the bottom edge of the iMac).

    • Squeeze the two display data cable connector arms together to unlock it from its socket on the logic board.

    • Pull the display data cable connector away from its socket on the logic board.

    • Be careful when disconnecting and reconnecting this cable, as it is easily damaged.

    • Disconnect the LCD thermal sensor cable connector from its socket on the logic board.

    • If your fan is spinning full speed after completion, check this connection or the hard drive's thermal sensor cable.

    • Carefully pull the display toward the top edge of your iMac and lift it out of the outer case, minding any cables that may get caught.

    • Before disconnecting the thermal sensor cable, take note of its orientation. It is extremely important to reinstall the connector reversed from the current orientation so the fans will not run at full speed.

    • Disconnect the thermal sensor by pulling its connector away from the side of the hard drive.

    • During reassembly, be sure that the thermal sensor connector is connected to set of pins closest to the SATA connectors. If the fans spin at full speed, reverse the connector's position.

    • Disconnect the SATA data cable by pulling its connector away from the hard drive.

    • Use the flat end of a spudger to help disconnect the SATA power connector from the hard drive.

    • Remove the two 9 mm T10 Torx screws securing the upper hard drive bracket to the outer case.

    • Slightly rotate the hard drive out of the outer case and lift it up off its mounting pins toward the top edge of the iMac.

    • Remove the two T8 Torx screws securing the upper bracket to the hard drive.

    • Remove the upper bracket from the hard drive.

    • Remove the two T8 Torx pins from the other side of the hard drive.

    • Carefully peel off the piece of EMI foam attached to the front of the hard drive.

    • Don't forget to transfer this to your new hard drive.

    • Only follow the next ten steps if you are replacing your hard drive with an SSD kit.

    • Depress the enclosure's front plate latch with your finger. While holding the latch down, swing the plate out.

    • Remove the front plate.

    • Line up the small SATA connectors so that the narrow side of the connector on the SSD matches the narrow side on the enclosure connector.

    • Slide the drive in through the front of the enclosure until the SATA connector is fully seated.

      • The SSD connects with the enclosure in only one way. If the connectors are not lining up, rotate the SSD and try again.

    • You may optionally install two Philips #1 screws that came with the enclosure kit to secure the SSD in the enclosure.

    • Plug the included sensor-enabled SATA power cable into the wide side of the enclosure's SATA connector.

      • The cable is keyed to connect in only one way. If you can't connect the cable, rotate it 180°, and try again.

    • Peel the backing off of the adhesive back of the small temperature sensor board.

    • Adhere the temperature sensor board to an exposed, metal area of the surface of the SSD, as close as possible to the SATA connector.

    • Fold the excess temperature sensor wires so that they are out of the way while you install the enclosure.

    • Install the mounting pins from the old hard drive onto the sides of the enclosure.

      • The holes on the enclosure may not be threaded, so screwing the mounting pins into them may require extra effort. Take your time and screw them in slowly, making sure they go in straight.

    • Attach any mounting brackets removed from the old hard drive onto the enclosure.

    • Connect the iMac's SATA power cable to the new temperature-capable SATA power cable.

    • Route the SATA cables where they will not interfere with any other components.

    • Connect the iMac's SATA data cable to the enclosure's SATA data connector.

    • Find a connector on the motherboard labeled HD TMP or HDD TEMP.

      • If you have trouble locating it, trace the two-wire temperature cable you disconnected from the old hard drive.

    • If the previous temperature cable is still connected to the board here, disconnect and remove it. You will no longer need it.

    • Connect the temperature sensor's two-wire red-black cable to the motherboard plug labeled HD TMP or HDD TEMP.

      • The connector is keyed to fit in one way only. If it seems like the connector is not fitting the socket, flip the connector and try again.

    • Route the excess wire so it does not interfere with any other components.


To reassemble your device, follow these instructions in reverse order.

315 other people completed this guide.


Make sure the hard drive is of the same producer and it has a temp sensor connector. It's the only way to ensure that the heat sensor connector will fit into the hard drive's socket. If you don't plug in the temp sensor iMac's HDD Fan will rotate at its maximum speed, ie. over 6000 rpms - the noise is extraordinary!!!

David Relich - Reply

I replaced my internal HDD on my 215" iMac, but the iMac can't get access to the new hard disk's (Seagate Barracuda Green) temperature sensor. The HDD fan in the iMac steps up the RPM, and over about 15min reaches 6000RPM (VERY loud) and stays there until machine is shutdown or put to sleep.

I found a fix for this: - this tiny piece of shareware software allows the iMac to see the temperature of the drive via S.M.A.R.T., and therefore the fans react according to the correct temperature again!

Ian - Reply

One thing Andrew left out here, which I discovered on my own, is that even if you have the temperature sensor connected to the correct pins, you ALSO have to make sure that it is 'oriented' properly.

On the sensor connector (the little head that plugs into the hard drive) I saw a little white dot on one side, which it turns out, indicates that's the 'top'. So on my iMac, you have to make sure when you connect the temp sensor connector with the white dot showing.

Otherwise, I got the 6000 rpm fans.

robert Seith - Reply

Success. For any interested people, it's about an hour - going slowly. Now that I've done it, I assume I could do it again in 15 minutes if I had to.

Just have the right tools handy, the T 8 and T 10 bits in particular. Getting off the display screen is easy. The screws are harder than you'd think because of the magnets, but they're not that bad. I recommend having tweezers to help pull them and place them later on.

Overall, the thing that worried me most was the fan issue. And, so far... it's not an issue. I had a seagate 500 gb, and I replaced it with a seagate barracuda 3 tb hhd. Everything fit right into it, just as it did into the original. No optical sensor needed. No new sensor needed, period. No software needed. Nothing. Just put in the new hd, and it works. I'm very pleased, and very proud of myself. Good luck to anyone considering doing this upgrade. You can do it, really.

Kevin - Reply

It's a pretty straightforward procedure. Took less than an hour. I replaced the 500GB Seagate Barracuda with a Seagate Barracuda 2TB, model ST2000DM001. So far, after about 30 minutes of use, it's working great, and I haven't had the fan problem, but we'll see what happens.

Kevin's advice about the tweezers for extracting and inserting the screws that attach the display to the case was right on (although I used a small pliers instead).

Before you begin the replacement procedure, I highly recommend putting the new drive into a hard drive dock, and restoring to it from a Time Machine backup. Try booting off the new drive once to make sure it works. Then, when you swap the new drive for the existing internal drive, it'll be ready to go with no further effort needed.

eshienbrood - Reply

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