Hello all, I have recently repaired the heater matrix in my Sovereign. It's a job which appeared daunting at first, particularly as I trolled my procedural information from various sources on the net, some of which were conflictive. However, the job's done, 100% successfully, so I thought I would post what I will modestly describe as the definitive "how to" on the subject, to assist others who may have the same task.
Why remove/repair/replace the heater matrix?
The heater matrix is basically a mini-radiator located under the dash, roughly behind the ventilation controls. Engine coolant is piped through the matrix, and air is circulated over it to be warmed and distributed via the ventilation system. They can develop a leak, which may manifest itself in a variety of ways. In my car, I noticed what appeared to be water vapour coming out through the dash vents and a smell of coolant in the cabin. There was also green coolant staining in both front footwells and a consistent coolant loss. I did drive the car for another 500km in this condition observing the symptoms, as I tried to deny the apparent magnitude of the job in front of me! I did a fair bit of cut-and-pasting from the Jaglovers site which was pretty useful. The best news is that the dash and the centre console do NOT need to be removed.
The first step is to remove the battery, the battery cover, and the connector for the earth strap to the firewall. There are two reasons for this: It's always good to disconnect the power when messing about under the dash, and it provides room to get a screwdriver on the two hose clamps that pass through the bulkhead into the cabin.
The pictures above show the two rubber hoses removed from the copper pipes. I suppose that if someone was really strapped for time, a quick temporary fix would be to simply block each rubber hose, or join them with a "U" connector. The car wouldn't lose coolant, there'd just be no heater - no great loss for me, but perhaps a bit problematic for those of you in the UK! Those copper pipes actually bolt direclty to the heater matrix. The final thing to do while under the bonnet is to get an airline and try and blow as much coolant as possible out of the matrix - just stuff the nozzle down each pipe in turn and wriggle it around a bit (which is something I haven't had much of an opportunity for since our kid arrived ). This is to try and minimise any coolant spillage in the cabin.
The next step is inside. Remove the passenger side knee bolster - the big cardboard-backed panel under the dash. From memory there may be an electrical connector to a small fan there somewhere, so be careful on removal. Once that is out of the way, remove the flattened black plastic pipe that carries the air from the console to the outlet.
Next, the relay rack needs to be dropped. This is held up by four screws. The front two screws need to be removed completely, but the back two can be slackened off and left in place. The rack can then be slid out of the way, and folded down. The photos below shows the rack unscrewed and folded down. I found that I had to unplug one connector, the white one on the left of the left picture, to allow sufficent movement, but this may not be the case with all cars. A close look at the right photo will show the two open-ended connectors on the rear of the relay rack that the securing screws pass through.
The next step is to remove the glovebox and lid. This is very simple. So simple, in fact, that I didn't take any photos of the removal process. My notes say to undo six little phillips head screws in the glovebox, and undo the two door hinge securing bolts. Be careful here to note the postion of any spacers that may adjust the fit of the glovebox door. I didn't, they fell out, and now I have to find the time to correct the fit of the door so it closes properly! Also remember that there will be electrical connectors for the glovebox light. The photo below shows the scene with the glovebox removed. The two copper pipes entering the matrix cover are clearly visible.
Now the end is in sight. The two copper pipes pass through a black plastic rectangular cover that is bisected diagonally. Use a magnetised phillips #2 to remove the four screws securing this two-piece cover, as they can fall out and be difficult to recover. Remove the plastic cover. Undo the two wires that are connected to some sort of electrical pot on the lower pipe. The left photo below shows the cover and the wires disconnected from the pot. Now, undo the four allen key bolts that secure the flanges of the copper pipes to the heater matrix itself. The right photo shows the bolts undone and the pipes disconnected.Once they are undone, the pipes are quite loose and can be removed if required. At this point, the matrix can be removed! It simply slides out through the opening. The matrix is originally fitted with some sort of felt, but this had mostly rotted off mine. It may assist in preventing rattle of the matrix in position, so have a think about this if required.
The pic below shows my matrix. The coolant leak is clearly visible. I took it to a radiator bloke who soldered up the leaky bar for little cost, and it's been fine ever since.
Installation is just the reverse. New flange gaskets will be required for the copper pipes - the radiator bloke supplied me with a couple of o-rings which did the trick nicely.
One last thing to consider is this: Does your car have any other issues which you should sort out while the car is dismantled to this stage? It's only a few more steps to remove the dash in its entirety, and it's not too big a job if you've got this far. I had problems with my ventilation system which I also fixed, so the whole job was done at once.
Looks messy, but only a few hours work!