A6 C7 Avant, intermittent no hot air

[Endeval]

Hi all,

2013 A6 C7 Avant, 2-zone heating.

Problem: No heating/hot air normally.  Intermittent issue, rarely works.

When driving, I have tried all combinations to get hot air without luck - A/C on/off, shuffling through blowing directions, hot/cold/max-hot, recirculate, windscreen, turn off/on, etc.  When the issue happens, the flow and return heater hoses to the heat core/matrix is warm, with the left-side flow hose hotter.

I have found on a number of occasions that starting the car again 30 mins later, the heating would work perfectly well, full heat at max blower.  

Example, I drive somewhere, park and return - heating is OK - but again intermittent.   Yesterday while about 30 mins into my journey with just cold air, I turned off the system for about 15 mins.  I then turned it on and had full heating, controllable from cold to hot.

 

Starting the car, I don't hear any clicking, etc which might suggest a stuck or slipping blender.
If I turn temps to minimum while on auto, I can hear re-direction, cold air and increased flow, so it *seems* thermostats are working (?).

Leading up to this, when adjusting direction from auto to windscreen, the screen would fog up heavily, as if there was water/moisture held.  Probably a red herring, but said I would mention it.

Heater solonoid/valve?  Bad Relay? 

All ideas welcome, please!

[audia4b5kev]

SLOW THERMASTAT

[a6blacked007]

Air in system 

[Endeval]

Hi all

Coming back to this now....I did some more testing.

I could be driving for an hour or two, still cold air....

if I turn off the car and ensure ignition is out and all off (open drivers door), when I restart the car, most of the time, I will have warm air almost immediately.  

 

Is there a chance it could be the hot water solenoid (heater control valve) gone or electrical issues?

 

p.s. my car never hits 90c water temp, about 75c - that could be coincidence, maybe a faulty temp sensor?

thanks!