[V6-12v] The smell of curry soup (blown heater core)

[Tom Christiansen]

Folks,

I bypassed my heater core and sure enough, the water consumption went
way down. So I had to bite the bullet and change out the heater core.
Most of my Memorial Day weekend went with that project. I'm certainly
glad I took a three-day weekend to do the job.

Replacing the heater core on a 1994 90S is not exactly what I would
call a difficult job, but it does definitely test your patience and
organizational skills. Here's roughly how it goes:

Parts needed: Heater core, O-rings for the A/C evaporator, A/C
restrictor/orifice valve, O-rings for A/C accumulator
(receiver/drier), A/C accumulator, PAG 46 A/C oil, coolant. Total:
Roughly $100 at Autohaus AZ, the stealership, and Schucks (I got the
restrictor there). Napa sells PAG 46 oil.

The following is free from memory. Follow at your own risk & expense.

0) Have your A/C system discharged.
1) Disconnect battery.
2) Remove the trim around the parking brake, gear shifter, etc.
3) Remove radio, center console. The switches for fog lights,
emergency flashers, etc., have connectors on the rear so the whole
thing can be unplugged.
4) Remove knee bars on both sides, glove box.
5) Remove steering wheel and driver's side airbag. Remove instrument cluster.
6) Remove passenger side airbag (big torx above glove box).
7) Remember to remove the little (8 mm) nut behind the radio on the
right hand side of the ductwork. It looks like it's holding the ducts
together. If you remove it, you'll have no trouble getting the dash
out.
8) Remove the dashboard.
9) You can now see the heater box/evaporator assembly thingy.
Disconnect the two connectors on its left side. Disconnect the
evaporator drain at its lower right, front corner. Disconnect the
cables for the ECU (on the evaporator assy between it an the
firewall). The connectors for the ECU has little tabs on the side
facing the firewall. Push the tab and the connector will slide right
out with almost no force needed. Remove anything that looks like it
might prevent the heater box from coming out (some octagonal impact
absorbing metal thingies come to mind).
10) Remove the air intake grille and external temperature sensor
located in the forward air intake plenum (opposite corner of the
plenum from the fuse box).
11) Remove the two nuts on the firewall. one above the row of
connectors. One below. The Bentley manual mistakenly show the nut
holding the connector bracket as being the one for the heater box.
12) Disconnect the evaporator A/C lines. Remove hose clamp holding the
boot around the evaporator connection. Pull the boot over the engine
side of the evaporator connection.
13) Push in the grommet around the heater core pipes.
14) Remove the heater box/evaporator assy. Yeah right... Sounds real
easy. Mine was fused to the insulation on the firewall. It took quite
a bit of cussing, swearing, sweating, thoughts of just getting a new
car, and almost giving up to get it out, but eventually it budged... I
ended up removing the airbag control unit and the footwell air
outlets. Don't know if that's necessary, but it made my life easier.
15) Replace the heater core (oh, yeah... that's what we were
doing...). The new core comes with some oily substance on it to
protect from corrosion. Do your best to clean that off as it'll smell
up your car when you have the heat on. If the two tabs holding the
heater core in place break off when you remove the old core, secure
the new core with two self-tapping screws. There are holes in the
heater box to accommodate these screws.
16) Clean up the ductwork, interior of the car, etc.
17) Assembly is reverse of removal.

I took about 5 hours disassembling the car to the point where I had
free access to the heater box/evaporator assy. It took another,
probably, 3-4 hours to get the damn box out. It took less than five
minutes to replace the heater core... ;-) A thorough
cleaning/detailing and assembly of everything took another, about 8
hours.

I should say that I organized everything in labeled zip-lock bags.
That took some time during disassembly, but probably also saved some
time during reassembly.

Sunday night I replaced the A/C accumulator. My A/C guy strongly
encouraged me to do so when I had the system open. The accumulator
contains some moisture absorbing material that gets saturated when you
have the system open. Given that the accumulator is only about $30
that seemed like a good idea. Remember to drain the compressor and old
accumulator of oil (measure the amount). Refill the compressor with 80
ml of PAG oil. Add the same amount of new oil to the accumulator as
you drained from the old one. Add an additional 30 ml to the
accumulator. Rotate the compressor by hand 10 revolutions. Have the
system recharged. Time to complete (not counting the recharge): 1
hour.


The key question: Would I go through this again? Probably not... I
never did get around to asking the stealership for a quote on a heater
core replacement. I guess it boils down to how much your three-day
weekend is worth to you. In my case I had a pretty nasty cold, so my
weekend was pretty much ruined anyway. But this is a really tedious
job that I would strongly recommend leaving to the mechanic. Unless
you really burn for doing it yourself.


Now I just need to find out why my external temperature display shows
an E instead of the temperature. Somehow during the ordeal, I must
have managed to pinch the wiring harness somewhere. Now the sensor
wire for the thermometer is grounded. The sensor itself is fine.
Another day, another project.


Tom