NOTE: Any time that you have the blower motor removed for service, inspect the air conditioner evaporator housing for loose insulation.  This is the housing on the passenger side (U.S.)  that the blower box connects to. (picture).  Loose insulation will end up in the fan, and cause failure of the fan controller.  Use an aggressive rubber cement to glue any loose insulation back in place (some people say to remove the insulation).   You can also remove the blower motor controller to gain access to the rest of it.  Moisture tends to defeat the glue after a while.  I found that the entire sheet covering the bottom of my evaporator housing was no longer glued down.

This write-up applies to both the heater core and blower motor.  Once the blower motor assembly is removed, the heater core is exposed.  If you're having trouble with one, you should consider replacing both.  Heater cores with quick disconnect hose fittings tend to leak.  Blower motors typically last about 100 K miles.  Here's what mine looked like after 105 K (picture).  As you can see, the commutator is wrecked and the brushes are very short.  At this point, this blower motor was running very erratically, if at all.

This job has a reputation of being a real bear.  Actually, on later cars it's only about a two hour job if things go well.  It's somewhat more difficult on 91 and 92 cars because there are some additional steps, a more so on the older 2.0 liter cars because the intake manifold is higher and that necessitates the removal of more stuff.  And it's somewhat easier on '93 and later models because of the way the false bulkhead was changed.  I think there are only a few tricks.  One is making room to get the blower box out and back in.  Another is knowing how far the evaporator housing can be moved.  And the third is knowing just what to do and how to do it; this write-up should solve that.

This was originally for a '91 but it's been updated for a '94 ('93 and later).  Earlier models appear to require removal of the wipers & wiper motor and the plastic trim at the bottom of the windshield.  Barry's write-up covers an earlier model, and includes wiper removal details.  His write-up is quite good, and very amusing, as well!  See his write-up:  Barry's heater core/blower motor write-up.  

Remove the aquarium cover.  Disconnect any vacuum hoses that get in the way (label them first).  Tie the cruise control vacuum hose up out of the way.

Label the heater hoses and disconnect them at the false bulkhead.  If you don't have disconnects at the false bulkhead, continue.  Only a little coolant will escape; let it drain.

Remove the false bulkhead (instructions)

Now select the ACC setting that runs the flap control rod (picture) farthest forward (full cold).  Turn on the ignition for a few seconds to allow the rod to move forward.

Label the heater hoses and disconnect them at the real bulkhead.  The job can be done with the heater hoses in place, but I just don't think it's worth it - removing the hoses gives you the room you need to get the box out and back in.  A 7mm socket on an extension and universal joint did the trick for me (picture).  If you have quick disconnects rather than clamps, you have an original heater core and should consider changing it out for one that doesn't use quick disconnects.

Unbolt the evaporator housing (on passenger side).

Remove the 10mm bolt that secures the power steering reservoir and the AC pipes (not applicable to later models).

Using a thin common screwdriver, slowly, carefully, progressively pry off the stamped sheet metal clip that retains the control cable on the flap arm (picture).  BE CAREFUL NOT TO BREAK THE ARM.  Mine did not have a clip and I did not replace it; I don't see any need for it.  If it doesn't come free easily, I would be inclined to cut it with diagonal pliers rather than risk breaking the arm.  If you don't have a magnetic tool to capture it, you'll probably lose it but it will probably show up later on the floor of the evaporator housing.

Disconnect the electrical connector for the blower motor.

Note: This section does not apply to 93 and later cars.  There is a secondary sheet metal piece bolted to the firewall that the false bulkhead sits in on the driver's side.  Remove the four 10mm bolts.  You will have to find two of them by feel, as they are not visible (picture).  One is behind the ABS relay box (it is one son-of-a-bitch to get to); the other is directly beneath the wiring harness (picture).  I did not reinstall these bolts, as I don't ever want to have to deal with them again!  Once all the bolts are out, remove the sheet metal piece.  You need to do this to get maneuvering room.  It's reported that it's a lot easier to remove the ABS relay box so you can see what you're doing here (thanks to Shahn Kariger).

There are some tabs at the bottom front sides of the blower housing that hold the housing in place.  Pix. I did not see these, but my '91's blower box had been mangled by someone who was in there previously, presumably to replace the heater core - the box was actually broken, and I had to put it back together with epoxy, using duct tape as a binder in place of fiberglass cloth.  I saw them on the '94.  The one on the driver's side can be pried and held released with a common screwdriver (the longer the better).  The one toward the center of the car is really hard to see, let alone get to; you could get it with a very long (18" or so) common screwdriver, but you don't really need to, as you can angle the box out without releasing that clip.

The box has a lip on the front (up at the top) that catches on a lip behind the top of the ductwork, and there may be a couple of spring metal clips up there normally. The bottom of the box has to rotate forward before the lip lock can be disengaged.  

In order to get the blower housing out, you have to pull the evaporator housing up as high as possible where it joins the blower box, and move the evaporator housing as far to the passenger side as possible.  This sounds delicate, but the whole assembly can be moved a considerable ways.  Lift it by the larger of the two pipes.  You'll probably have to get atop the engine head to do it effectively.  A second person is extremely helpful here, though I've always done it by myself.  Just remember that the evaporator housing will move a surprising amount; be careful but be persuasive.  Shahn recommends using a sturdy rubber bungee cord to hold the assembly up out of the way, an excellent idea.  Pic.  The blower box must be rotated forward at the bottom to disengage it, then it must be rotated out from the right with the evaporator housing raised and moved left.  It's tight, but it will come out.  Picture.  The evaporator has to be raised even higher to get the heater core out, and it gets really tight, but it CAN be done (picture).

Separating the box halves (pictures) - The box halves are held together by a single screw, a snap-on crossbar and four (if they're all there, which is doubtful) plastic clips.  The crossbar goes across the opening of the box, where the flaps are - let's study that first, because it has to be removed and it's not easy to describe how it goes back together.  Rest the motor housing on your left knee, with the cable on the right.  Look down into the opening where the flaps are - the flap handle should be on your left and toward your body.  Note the tab on the left; it's about 2" tall and an inch and a quarter wide.  It's on the left - that's the key.  Also, there's a brace that goes from the center of the crossbar to the top of the box, away from you.  Rotate the assembly 90 degrees to the right so you can see the left end.  Just above the flap lever there's a tab that goes into a hole.  lift the end flap a bit with a fine screwdriver and you can release the tab.  Same thing on the other side, only note that there's an extra flange there.  So anyway, that's how it goes together.  And how it comes apart too, so release the tabs and remove the crossbar.

Remove the single (T20) screw in the center.  It's on the side where the leads come out, only it's way in at the center, between the motor housing and the outlet box.  Remove the clips that hold the halves together (four, if they're all there) - they're about 3/8" tall and 5/8" wide, black plastic.  Try to keep the flap pivot pins installed in the non-motor end of the housing when it's apart - if you don't maintain the alignment of the flaps, it can be pretty confusing to get them back together correctly.  I prefer to line the flaps up in the cooling position, which is to say, in the same plane with each other, forming a continuous wall along what would be the back of the box when it's installed.  Separate the two halves of the box and put the non-motor half aside.

Removing the motor - Remove the screw that holds the motor in (see previous pictures).  I had to drive the motor out of the housing.  First I reinserted the motor retaining screw and hammered on it until it bottomed.  Then I used various long skinny screws/tools to drive it the rest of the way out.  It was tight, and I pretty much destroyed the motor.  Ridges in the housing make for a press fit for the motor.  Some silicone spray on those ridges might make it go better.  Picture  You'll need to remove the connector pins from the connector housing.  First, use a felt-tip pin to mark the wire colors on the connector housing.  Now pry the rear of the flat side of the connector up.  It's hinged and when you pop it loose you can pull the pins out.  Now you can pull the wires through the hole in the motor housing.

Replacing the motor - Transfer the fan cage from the old motor to the new one: support the back of the fan cage in a vise, then gently drive the motor shaft out with a hammer and suitable drift (a screwdriver will probably work) (picture).  Rest the rear end of the shaft of the new motor on a solid surface, then gently tap the fan cage onto the shaft (picture).  NOTE: It's important that the rear end of the SHAFT is supported when you drive the fan assembly onto the shaft.  Spray silicone lubricant on the cable boot to help it go into its hole in the plastic case.  Grease the ridges in the housing and the new motor will slide right in.  There's a channel in the plastic housing for the wires, and it should guide the motor properly into position.  Feed the wire ends through the hole for the cable, then push the motor into position.  Reinstall the wire connectors into the plug housing, then snap the housing shut.  Pull the cable boot into position - carefully use a flat-bladed screwdriver to lever it into position if necessary.  Don't forget to install the motor retaining screw (I added a washer to the one on the '94 because the plastic was wearing thin where the screw came to bear).  Reassemble the box halves, making sure that you get the flap linkage right (it can be tricky, but basically the flaps operate parallel to each other) Pictures.  Now install the cross-brace across the opening.  If you forget to install it, the flaps will fall out, things will get bound up and you'll probably break the linkage between the flaps.  I like to run duct tape around the joint between the box halves to ensure a good seal (also compensates for lost clips).  Connect the power cable and test the blower before installing the box, but remember to just turn the ignition on without starting the engine (heater hoses are disconnected).

Pre-installation check list: 

Blower assembly installation - Stick the left end of the box into the opening, such that the fan cage is facing you.  For 93 and later cars, lift the right side up and over the partial false bulkhead; for all cars, lift the right side of the blower assembly up and tilt it at about a 45 degree angle, while at the same time tilting it about 45 degrees forward.  Move all cables and hoses out of the way, make sure the evaporator housing is pushed to the left, and the blower assembly should go into the cavity.  Slide it in in, trying to engage the fan opening with the evaporator opening and the upper lip of the blower box with the lip on the car, rotating it in at the bottom.  It's usually quite a struggle, but if it just seems impossible, make darn sure that the cross brace is installed on the blower box.  The only time I just couldn't get things to line up was when I left that brace off and the flaps fell out and got all tangled up.  I broke the linkage between the two flaps and it cost a lot of money to straighten things out (plus I had to do the damned job all over again!!!).  Another thing that will make it near impossible is not having removed the heater hoses.  Once it lines up, it should snap into place.  If your retaining clips have gotten busted, you can shore the box up with wads of foam rubber, which held it tightly in place and will take care of any rattles.  

Reinstall the actuator cable on the plastic flap arm.  You purists can put the retaining clip back on if you insist, but I tend to leave it off.  The only time a clip would be needed would be if the flaps jammed, in which case I might want the actuator cable to come off anyway.  Re-installation of the cable in that case would only require removal of the aquarium cover and the false bulkhead.  I've been running without the cable clip with no problems.

Reinstall the lower sheetmatal piece on earlier cars(I only used the two left screws on my '91).  Reinstall the heater hoses.  Reconnect all the connectors (including the four-conductor one beneath the throttle body on earlier cars). Reconnect any disconnected vacuum hoses, and check the crankcase vent stuff on top of the engine to see if any of it got knocked loose.  Reinstall the screws for the evaporator housing.  Gather up all loose tools, reinstall the false bulkhead and reinstall the aquarium cover (don't forget to connect the washer hose to the bottom).