No cabin heating.

[Darashen]

1.8t 2005 cabrio.

I have spontaneously lost the cabin heating, just blows cold air.

I am about to go out and drop the glove box to check the heater flap motors but as both sides have lost heat I don't expect this to be the problem.

Bypassing the cabin temp sensor by putting climate control on high makes no difference.

I don't have access to vcs so I am limited to old school diagnostic techniques.

Is this likely to be a blocked heater matrix or could it be something else playing up. Any ideas welcome.

 

[pauldazzle]

Flap motor would be my first suspect.

 

[Darashen]

Dropped the glove box and found all motors functioning correctly.

Test run established I get partial heat over 40 mph. Engine temp is spot on so thermostat is fine so I suspect a blocked heater core.

Only question now is flush it or replace it.

 

[pauldazzle]

Check the 2 heater hoses that go through the bulk head to the Matrix. If they're both hot the Matrix is ok.

 

[Darashen]

Bottom hose gets hot but top one is cool. Suggests it is a blockage in the matrix.

Have tried to get the hoses off at the bulkhead but they are stuck on. Will order a hose removal tool and have another go aylt back flushing the matrix next weekend.

 

[Darashen]

All sorted. Fitted a new matrix today. Now have a loads of heat in the cabin.

For anyone else who tries this whilst the matrix fouls on the brake/clutch pedal bracket it will come out. I used gloves with rubber palms to get a good grip then just kept pulling/wiggling it until it came free. New one went in with no drama.

Why is the a4 such a pain to bleed the coolant system.

 

[KennyJB]

I am having similar issues with my 04 cabrio.
Started fairly recently with getting cabin heat for around 5 mins then it blows cooler air. Today I tried flushing out the matrix which at first seemed like it worked. I had the car sitting on the driveway running for 20-30 mins and it was all quite hot with the heat coming from all vents. I thought that was it fixed. Until I went for a drive. Again for a few mins the heat was there then it went back to cooler air from the vents.
On checking the pipes in the compartment next to the battery, both the pipes are hot which I believe is supposed to rule out a matrix problem. Anybody had this before or any ideas on what to check next?