2015 B8 Heating/climate control problem?

[Dan0811]

Hi all, I've got a 2015 B8 2.0 TDI (163bhp) SE Technik. Not had the car long but it seems I can only briefly get warm air out of the passenger side vents on very low fan speed ( max speed 4 of 12 ) and the drivers side is always cold. 

Initially I suspected an air lock or blocked matrix, ive tried to bleed the matrix inline with the Audi workshop manual. However after that not working or making no difference I discovered that apart from about 1/2 a pint of coolant on first start up, notuing is being fed to the matrix in the first place.

Anybody had this before ? I'm a  mechanic myself so just thought I'd ask before I possibly go digging down wrong paths. 

Edited January 7, 2024 by Dan0811

[mcurtiz]

I think have this same fault or similar, so interested to see suggestions/fixes.

What I've done so far:
I replaced the A/C pump and A/C rad as I suspected them because last summer I had no cold air -only hot(!), and had a really noisy AC pump! This fixed the noise and A/C cold but no heat!

Now, fault code said RH side flap motor had unfeasible response so replaced with a new part, recalibrated the flaps, but still didn't work so put the old motor back in to rebase my investigation and damn it, it now worked (=dodgy connection?) and I could see the flap opening/closing - but it didn't fix the symptom of zero heat on the drivers side -and low heat on passenger side. Fault must be deeper inside as there is no heat coming from the central duct i.e. before it even gets to the driver's side footwell.

[cliffcoggin]

I have read reports on this forum of a bag of silica gel in the cooling system breaking up and clogging the heater matrix. I don't know which models are affected by this problem, so it would be worth searching the forum history over the past year for more information.

[mcurtiz]

44 minutes ago, cliffcoggin said:

I have read reports on this forum of a bag of silica gel in the cooling system breaking up and clogging the heater matrix. I don't know which models are affected by this problem, so it would be worth searching the forum history over the past year for more information.

I would never have believed that VAG would do such a crazy thing - just viewed a really useful YouTube vid on this.  I suspect this maybe too late for me though...

 

[cliffcoggin]

So is your expansion tank marked "Mit silicat"? If so, that is likely to be your problem.

[mcurtiz]

My tank does not have the "Mit Silicat" (German for "With SIlicate").

Apparently, the round spherical tanks have this marking if they have the silicate bag. But, different shape tanks 'might' have a silicate reservoir (so no bag) with a labyrinth to prevent premature Silicate dispersal but there does not appear (yet) to be a list of which models have a bag or which have a reservoir -but it seems ALL models have silicate as this prevents premature corrosion of aluminium surfaces/parts.

This suggests its not the silicate that is the problem as that is needed, but the bag. Once burst, logically it goes with the flow and chokes the parts with the narrowest pathways - the heater matrix!

[cliffcoggin]

17 hours ago, mcurtiz said:

but it seems ALL models have silicate as this prevents premature corrosion of aluminium surfaces/parts.

It may well be all current models for all I know, but not necessarily all years. I am fairly certain my 2007 A3 did not, so it must be an innovation that was introduced since then.

[mcurtiz]

7 minutes ago, cliffcoggin said:

It may well be all current models for all I know, but not necessarily all years. I am fairly certain my 2007 A3 did not, so it must be an innovation that was introduced since then.

I've been reading up...

Silicate has always been needed since aluminium-based parts were introduced c.1996, to prevent aluminium surface corrosion (such in as the rads / heater matrix!). It was introduced post-cast iron blocks and brass rads etc.

I also have an A3, a 2011, that also does not appear to have the bag -at least it does not have 'Mit Silicat' on the expansion tank and uses G12 (pink or red) coolant. I do wonder if the bag or reservoir is there, just the marking is missing. I say this because G12 does not contain silicates apparently hence supplemented silicate would logically be needed.

FWIW - G12 is made of 5% distilled water, ethylene glycol alcohol, 2+ carboxylate compounds and a colourant. G12 life is 4-5 years / 80k miles. G12 freezes at -50c, boils at 118c.

G12+ (red) and G12++ (purple, c.2008) are also available and are long-life organic coolants and do contain silicates combined with carboxylate to overcome the weakness of G12 that only works when corrosion has appeared.

You shouldn't mix G12 with G12+ (and def not with G11) or even G13, etc., so full flush out is needed if using different to what is in the system. Everything I read recommends sticking with the recommended coolant and not to mix  - although moving from the recommended G12 to G13 on a full system flush basis is generally acceptable but usual caveats apply (check first etc).

I also have 2015 Golf that does have 'Mit Silicat' (so will be swapping its expansion tank as a precaution!) using G13 coolant. The main difference in G13 is Propylene Glycol (less harmful to the environment when disposed but also in its production) and like G12+/++, contains silicate. G13 came into force c.2012, freezes at -69c, boils at 175c and has a similar life span to G12.

A change of the coolant colour from its original (bright orange, purple, red, pink) indicates it is losing its protective properties. 

With all that said, having gone down a rabbit hole on coolant and silicate bags and what-not, I am still no closer to knowing why my A4 does not have heat on the driver's side!

[cliffcoggin]

Let's not confuse a soluble carboxylated silicon compound with silica gel. They are two different things. Amongst some of the uninformed nonsense I have read on this subject is an opinion that silica should not be used because it is abrasive, and indeed silica is abrasive, but silica is not what is added to antifreeze. Silica is not the same as silica gel which is not the same as a carboxylated silicon compound.

The soluble carboxylated silicon compound is a corrosion inhibitor that reduces the electrochemical reaction between iron and aluminium. It is not solid and therefore can not block coolant passages. (Incidentally aluminium has been used in engines for many decades before 1996.)

Silica gel beads on the other hand are used throughout the commercial and industrial worlds for absorbing water, which I presume is their function in the expansion tank, because most hydraulic fluids are hygoscopic, i.e. they absorb water which degrades their performance. For example you will often find small bags of silica gel beads in the packaging of steel and iron goods to protect them from rust during storage by keeping the atmosphere dry in the pack.

None of which gets us any closer to solving your lack of cabin heating. I don't know if the absence of a Mit Silicat mark can be taken as proof that there is no silica gel present, so you have nothing to lose by back flushing the entire cooling system in stages.

As the scale of this silica gel problem becomes more apparent to me, I now wonder if some of the reports we get on the forum of unexplained low engine temperatures are related. I imagine that these beads can easily prevent a thermostat from fully opening or fully closing. They could also be clogging the coolant pump, which of course is designed to pump liquids not solids.

[mcurtiz]

@cliffcoggin - not sure who mentioned silica gel but no confusion on my part.

If you are referring to my mention of silicate bags and reservoirs, they are used in various VAG models - small bags or reservoirs of silicate (not silica gel) in the expansion tank. There are reports that describe the bags decomposing or rupturing and the silicate distributing around the cooling system and so the theory is that this blocks the heater core due to its inherently narrow channels. 

Edited Saturday at 04:26 PM by mcurtiz

[mcurtiz]

Problem is now solved FWiW!

I decided to flush the heater core (only) to see if there was any blockage - theory being that as some heat could be felt on the passenger side but none on the drivers side, suggested to me a partially blocked heater core. It's not a single capillary path in the core but a classic radiator style matrix.

Method: I disconnected the hoses to the heater core in the scuttle area between the fire wall and bulkhead. It was a PITA but I got the hoses off. I  connected some garden hose (softened to get it to expand from the 1/2" bore to the c.25mm pipes of the heater core). I hooked it up to mains water and ran water through the core in both directions (i.e. reversed the flow). There was what can best be described as sand-like sediment but not a lot.

Reconnected the hoses, topped up the coolant, and ran the engine for c.15 mins, with the heat and blower at maximum. Heat was now coming through all vents.

When the weather improves (or the fault returns!) I will do a full additive-based system flush then refill with the recommended coolant. 

Edited Saturday at 04:27 PM by mcurtiz

[Sid2020]

11 minutes ago, mcurtiz said:

Problem is now solved FWiW!

I decided to flush the heater core (only) to see if there was any blockage - theory being that as some heat could be felt on the passenger side but none on the drivers side, suggested to me a partially blocked heater core. It's not a single capillary path in the core but a classic radiator style matrix.

Method: I disconnected the hoses to the heater core in the scuttle area between the fire wall and bulkhead. It was a PITA but I got the hoses off. I  connected some garden hose (softened to get it to expand from the 1/2" bore to the c.25mm pipes of the heater core). I hooked it up to mains water and ran water through the core in both directions (i.e. reversed the flow). There was what can best be described as sand-like sediment but not a lot.

Reconnected the hoses, topped up the coolant, and ran the engine for c.15 mins, with the heat and blower at maximum. Heat was now coming through all vents.

When the weather improves (or the fault returns!) I will do a full additive-based system flush then refill with the recommended coolant. 

Glad you got it fixed the way you did. If it’s a stubborn blockage I’ve known a power wash to be used on the garden hose instead of mains water pressure