C5 Mk1 2001 2.2HDi Hot air ducts leaking behind dashboard

[aspire_helen]

The colour screen Multi Function Display (MFD) went blank recently on a winter run up the motorway. Subsequently, it has operated OK. The usual suspect is the 22SY451 ECU. I noticed the air behind the instrument panel was remarkably warm. I discovered that the foam seal between the top output of the heater unit and the fascia vents had perished into a sticky black mess. Hence, hot air from the centre facia vents is leaking into the space behind the dashboard where the 22SY451 is located. Subsequently, I fitted a temperature probe to the ECU Central Processing Unit (CPU) and a larger cooling fan to the casing. With fascia vents deselected, and with the extra cooling fan running permanently, the CPU settled at about 40degsC. Computer CPUs should run at 40 to 50degsC. I now need to seal the leak (expanding foam?) but access is limited. I also noticed the alternator was pushing out 14.9V, so I intend fitting a 12V regulator to the ECU's power supply, and play around with a Peltier cooling chip to reduce both the voltage and thermal stresses on the aging chips.

[aspire_helen]

Just an update. I explored a new alternator regulator, but when I dismantled the original alternator to verify the type it was apparent the slip rings needed replacing also. I was lucky enough to find a new Fohrenbuhl FA5008 alternator "last one" going cheap at only a little more cost than a new regulator + slip rings. Once fitted, the new alternator put out 14.8 to 14.9V - doh!
I purchased a 12v Peltier cooling kit on Ebay with a TES1-12704 4cmx4cm (4 amp) chip, heat sinks and fan. As a trial, fixing the chip direct to the ECU outer casing brought the casing temperature down to 6degsC in 21degsC ambient air. Bench tests to continue!

[aspire_helen]

Update - gap re-sealed.

I have investigated the extent of the perished foam seal using probes and an endoscope via the gap left by the seal. I also tested the airflow from the fascia vents in an attempt to determine any leakage around the passenger and windscreen duct sections of the seal. Although it is obvious that the seal around the drivers centre duct has gone (visible and accessible behind the instrument panel), it is equally obvious that all the foam seal is failing, or likely to fail, on the passenger side and windscreen ducts.

10mm gap where the foam seal used to be

The perished foam is exceptionally fragile and can be squashed into a black sticky smear

Three of the 4 sides of the drivers duct had gone leaving a 10mm gap. The fourth, between the drivers fascia duct and the windscreen duct, was visibly intact on the endoscope. Testing the airflow through the gap, using a wind meter in ft/sec, showed that it was effectively a third vent directing driver’s fascia air into the void behind the dashboard. In addition, airflow measurement also indicated that there was some windscreen air leaking into the passenger fascia ducts.
The foam seal has deteriorated such that it has no substance and can be squashed into a sticky black smear between the fingers. However, it has left behind the sticky self-adhesive backing on the face of the heater unit; the face of the mating surface on the dashboard is smooth. To replace the seals, I cut 3 suitable strips of high density pipe insulation (yellow); 2 for the sides (135mm long) and one for the end piece (120mm). The side strips have to have some rigidity to enable them to be pushed end-on into place. On the plus side, any residual foam seal just got squashed out of the way. On the negative side, the remnants of the adhesive backing cause some restriction, so I used some silicone oil lubrication to defeat the stickiness. The end strip was easily forced into place. I confirmed good placement with the endoscope; the yellow foam provided good contrast on the screen. However, something like a flexible ruler could be used to guide the side strips into place.
As to the remaining sections of the seal. The passenger duct section may be accessible behind the glove box – tbd? However, the windscreen sections are impossible to access without removing the dashboard – nooo! So, there is another potential solution. I believe all the remaining foam seal could be easily pushed and squashed out of the way working only from the drivers end, although this runs the risk of sticky remnants falling into the motor driven louvres below! That is why, for my repair, I chose not to fish out the old seal, but allowed the foam side strips to “squish” it as I forced them in, end-on. That worked for the relatively short strips (135mm), but longer strips would buckle, depending upon the stiffness of the foam strips. Then the gap could be filled by feeding sections of suitably-seized, expanding foam strip (eg Xpanda) from the drivers end. This foam seal comes compressed to about 25% of its final thickness, which then expands ”slowly” when released. Hence lengths of a compressed thickness of say 5mm could be fed into the 10mm gap, and aligned, which would then expand. Tricky, but I think do-able.

For reference, below are the airflow results after the re-seal in ft/sec. Each row reads left to right across the fascia ie passenger side vent, pass centre, driver centre, driver side, noting that the centre vent airflow control is common to both.
790, 820, 1040, 880
closed, 1220, 1060, 950
closed,1240, 1450, closed
closed, closed, closed, 1460
1400, closed, closed, closed
990, 900, 200, closed

Endoscope of surviving seal between the drivers fascia duct and the windscreen duct

Using an endoscope through the gap

The foam seal around the fascia and screen ducts between the heater and dashboard (not mine)

The gap filled by high density foam (yellow)

A possible better gap filler, next time

[MattBLancs]

Good bit of investigation work and fix there.

Was going to suggest foam draught strip when I had read about half way through, but by the end see you'd reached the same conclusion.

This is 12 mm uncompressed, so could be just the ticket
https://www.toolstation.com/stormguard- ... rip/p95977

Have a roll of this, use it to stop stuff rattling/vibrating but would guess would suit your needs too here,

Matt

[MattBLancs]

Wind meter as in egg cup anemometer or turbine type?

[aspire_helen]

Hi Matt, just taking a "brake" from the Clio.
I tried various types of foam. The problem is that it has to have some rigidity lengthways to resist it buckling when pushing it in end-on. Access behind the instrument panel is very limited and the remaining seal and its original adhesive backing is very sticky, making it difficult to feed/push a soft foam seal into place. It will be a lot easier to feed in and accurately position the compressed seal. It will still need some DIY tools to guide it into place.
I note 2 recent threads looking for 22SY451's replace or repair, which was the issue that first brought my attention to the very hot air behind the dashboard.

[MattBLancs]

Ah, yes understand your issue. That draught strip stuff is very soft, wouldn't entertain being pushed sideways into the slot. If easily dismantled, then could clean all the old adhesive off - then would suggest feeding the draught strip in complete with the backing paper, then when in position it's possible to leave the foam stationary and extract the backing paper from under it. Quite awkward to do but I did that with it before (can't think what the application was though!)

However, if easily dismantled then would be in a position to glue something else into place - so the above unlikely the best option then either.

Think your closed cell foam pipe insulation is a good solution, and leaving the gunk there to help bond it in place also sounds good way forward.

And an excuse to do something other than fight the Clio brakes, all the better!

[aspire_helen]

"Easy" dismantle is remove the dashboard!!!

[aspire_helen]

I finally got around to checking the passenger side of the foam seal around the fascia and screen ducts, by removing the glovebox. Simply put......there isn't any! The foam has perished and completely blown away leaving a 10mm gap through which the air destined for the fascia vents is leaking into the dashboard.
Access to plug the the gap as before is limited, nowhere near as good as the driver's side, but do-able I think.

[GiveMeABreak]

Sorry to hear that, it sounds as if it's just decomposed like most of this stuff is designed to do. Given your car is over 20 years old, you'll find this starting to happen.

I suspect with the current recycling hysteria that most of our newer cars are likely to be melting away when thy hit a certain date!