Here are the steps for the heater core replacement on a 5 Doors 900SE turbo with back seat heating, manual transmission and ACC. For other models especially the ones with manual AC the job may be different and longer. It’s a lot easier than it looks. Good luck!
1-Remove the rear seat ashtray from the center console rear end.
2-Remove screw behind ashtray and lift L shaped rear piece of central console which include lid for coin/cup space.
3-Remove the 2 M6 nuts that are visible when the ashtray is out.
4-With a small flat screwdriver pry in the small indent at the front of the windows/locks switches panel in the center console. Pry out the front end and lift the swiches assembly.
5- Carefully press one end of the long wire connector terminal to disengage the locking dent then swing the wire connector out of the hinge at the opposite end. Put switches assembly aside.
6- Put your fingers in the opening of the switches assembly and at the same time with a small flat screwdriver pry the rear seat-heating switch out. Disconnect the wire connector by pressing the two locking strips at opposite side simultaneously while pulling the switch and connector apart. Put switch aside.
7- Stick your fingers in the front of the switches assembly opening and by touch look for one of the two flat protrusions that locks the small ignition key square panel rear end onto the front part of the center console rear end. The two flat protrusions are aligned transversely at the opposite sides at the rear and engage in two holes on the piece under it. With your finger try to feel the protrusion and push it up while pressing forward to disengage it from the hole. Do the same at the left corner by putting your finger in the front end of the hand brake lever opening. Once the rear end of the ignition switch square panel is lifted gently remove it from the tab on the front part that engages on the trim were the gearshift lever comes out. This small square panel under the ignition key can be a bitch to remove
8-Remove the cabin light switch, remove the two screws under the ignition switch panel and remove the center rear console.
9- Pull out the shift gear leather boot from the trim of the front center console.
10- Remove the two side panels on each side of the front center console. To remove the right one open the glove box compartment remove the screw on the left end of the opening and remove the lower screw located almost on the floor. Push the panel forward to disengage it from the center console (you should not need to remove glove compartment). Do the same on the driver side.
11-From behind the center console where the side panels were, push out the ACC assembly, disconnect the wire connector in the same way of the windows switches assembly.
12-Still from behind push out the heater seat switches and disconnect them.
13-Still from behind disconnect the cigarette lighter two connectors. When pulling the one for the light be careful not to loose the little plastic thing that surround the little bulb.
14-Push from behind/pry from the front the switch plugs next to the seat heater switch.
15-From the front, gently pry out the “bull eye” cabin temperature sensor cover from the center console above the ash try. With a screwdriver press down the tabs from the front and push the sensor assembly in to remove it. Disconnect the cables. Since the sensor fan often become noisy (see bulletin board), take the opportunity to lubricate the sensor fan motor out by putting a drop of oil on the small fan motor shaft. The rear end of the motor can be slide out by lifting the two tabs.
16-Put your fingers inside the opening where the ACC was and look for the two plastic pins that hold the center console together with the dashboard. With a screwdriver pry them out. Now you can remove the center console front part.
17-Disconnet the front end and remove the air duct that that runs between the seats.
18-Disconnet the two side ducts that take air to the rear floor areas and leave them dangling attached to the wires.
19-In front of you is the black box that contains the core. It has two lids to open it.
Put a long flat screwdriver on the side between the metal frame and the box and look for a tab on each side. Pop it up. The top lid of the box will open.
20-Do the same with the bottom lid. The tabs are still on the sides but lower.
21-There is the heater core you got it!!
22-Drain the cooling system by opening the drain cock on the left bottom corner (driver side). Or disconnect the big hose from the opposite bottom corner.
23-Disconnet the hose that goes to the heater from the cylinder head. It is the one that gets bigger where it attaches on the cyl. head.
24-If you have compressed air available blow it in the hose so to push the coolant out of the heater core. If you don’t have air you can use a garden hose.
25-Go back inside and unclip the collars that keep the pipes in the core. You need a very small flat screwdriver to pry up the tab on each collar.
25-Press down the pipes and pull out the core.
26-Inspect it for signs of leaks (oxide deposits and dried up coolant).
27-If the core is OK get two new o-rings and install them with some O’ring grease (castor oil grease). Do not use any grease because some may not be compatible with the rubber.
28-Fill the cooling system, run the engine till hot and check for leaks at the core.
29-Put everything back in reverse order.
30-You saved yourself lots of $$$$$$$!!!