Heater matrix windscreen mist

[tonyp1]

COULD MY HEATER MATRIX BE LEAKING.
2003 Passat SE 1.9 tdi PD engine code AVB
The lower part of the windscreen is misting up about half the size of a saucer where the dashboard meets the windscreen glass very slightly just off centre towards the driver side.
I can often see a small amount of vapor/mist rising from between the screen and the dash molding.
This happens a few miles after the engine temperature is at normal 90c. The engine never overheats.
The upper blower vents are on full with a low temperature of 18c selected.
The re circulation function is not selected and not showing on the display.
The outside air temp is 29c The pollen filter is new and the aircon does not work so is not on. All carpets are dry. This is happening in the recent dry spell, hot with no rain.

I conducted a test while driving by selecting the de-mist function and increasing the heater air temperature on full air flow and the whole screen fogged up on the inside. The coolant level when checked cold does not seem to drop.
My gut feeling is that the heater core has developed a very slight leak.
Has anybody experienced this problem before? any help would be much appreciated.

[The Glassman]

COULD MY HEATER MATRIX BE LEAKING.
2003 Passat SE 1.9 tdi PD engine code AVB
The lower part of the windscreen is misting up about half the size of a saucer where the dashboard meets the windscreen glass very slightly just off centre towards the driver side.
I can often see a small amount of vapor/mist rising from between the screen and the dash molding.
This happens a few miles after the engine temperature is at normal 90c. The engine never overheats.
The upper blower vents are on full with a low temperature of 18c selected.
The re circulation function is not selected and not showing on the display.
The outside air temp is 29c The pollen filter is new and the aircon does not work so is not on. All carpets are dry. This is happening in the recent dry spell, hot with no rain.

I conducted a test while driving by selecting the de-mist function and increasing the heater air temperature on full air flow and the whole screen fogged up on the inside. The coolant level when checked cold does not seem to drop.
My gut feeling is that the heater core has developed a very slight leak.
Has anybody experienced this problem before? any help would be much appreciated.

AC on or off?

[Col]

Yes, heater matrix.

I had this on my Passat. I was in denial of it for over a few years but eventually saw a drip of coolant on the car mat where it came out of a heater duct.

Symptoms are as you describe, soon after warm up the windows would fog, especially in cold weather.

I swapped out the matrix myself and it is quite a job. You will need to get the A/C de-gassed and re-gassed also.

These are my adventures of dealing with it. The matrix issue starts at the end of page 5
My B5.5 TDI diary.

And here when I was asking about window misting
Question Greasy haze on window interiors

[tonyp1]

The AC is off. It loses it charge after about a year and has been re gassed a couple of times but eventually the 600g gas charge reduces to about 270g this is the amount extracted at the last regas about a year ago. The air con is not used just cold air. When the cold blower is used is the air drawn over the AC evaporator even with the AC switched off ?
The mist on the screen seems to have a very slight greasy feel to it when I try to wipe it of although when switched of and left standing for a couple of hours the mist/ condense seems to clear.
Many thanks for your reply its appreciated.

AC on or off?

[tonyp1]

Thanks Col your reply is much appreciated. I have had the car from new and now done two hundred and three thousand miles and it is very well maintained and in excellent condition so want to resolve the issue if possible. A local guy has the same car with 207500 on the clock but never had this problem.
I've worked on vintage restorations and 60s & 70s rebuilds all my life but this modern stuff is just a bit more involved ! Thanks again.

[Col]

I'm just a keen DIY'er so if I can do it you most certainly will.

Obviously lots of dismantling involved but nothing impossible. I spent a lot of time working out what needed to come off and how to undo it. The answer is everything.

A few tips; there is a single screw accessed from the engine bay side that holds the crash bar along with the many other inside on the crash bar; the steering wheel doesn't need to come off but you'll need to support the column on an axle stand; make sure you mark the switch plugs on the center console.

The matrix istelf is fairly cheap, it is up to you if you want to replace the a/c evaporator again whilst it is all off and in bits makes sense as it is quite cheap. You'll need A/C line 'o' rings for the evaporator along with some pag oil to assemble them anyway.

Please report back on how you get on with it.