Help is appreciated . 2015 Q7 TDI. 123k miles Suddenly, no heat . Fan runs and speed can be varied with the ****. A little bit of heat can be felt at the vents. Engine heat gauge is at its usual display setting. Radiator hose going to drivers side of the radiator is hot but returning hose is cool.
mechanic replaced thermostat, Water pump, blower motor (said it had intermittent faults). Heater core shut off valve. Problem returned after a few 100 miles.
Now a new shop says all of the lines are plugged with corrosion and need to be replaced and possibly the heater core as well. Cabin air filter also was replaced.
I find it hard to believe everything failed at once, but am so far into this $$ wise I want it fixed. Has anyone had a similar experience?

 

It didn't all go bad at once, but mechanics gotta eat, drink, and make their boat payments too, right?

You mentioned the return hose is cold, which means the hot coolant is not getting through the heater core, and those typically go bad from...internal corrosion linked to the car not getting coolant changes as scheduled, or somebody adding tap water to backfill the reservoir with, rather than distilled water, as is called for to prevent corrosion internally.

You may or not have needed the blower motor, as those are pretty common failure point with some age on them; on our '15 the HVAC blower (front) went out around 120k miles. Those do tend to make some noise to let you know they are going out though.

Offhand, my gut tells me the mechanic has just been stringing you along, based on everything that's been replaced in the 'attempt' at fixing your no-heat issue. Not that any of those things were terrible to do on your older Q7, but not really addressing the underlying issue, which would seem on the surface to either be a blend door related problem, which prevents hot or cold air mixing into the output, or that there's simply nothing getting past that heater core.

If there is a blend door/actuator type failure, then that normally shows up in a diagnostic scan result. The heater core itself is simply an isolated problem you arrive at via a process of testing/deduction, which is why I think you've been taken advantage of by the first shop, or they were doing troubleshooting like Audi does it...replace a part and see if the problem goes away. Rinse & repeat.

 

Yeah, i think I was (and maybe still am) being strung along. I willadmit its been 60k since a coolant flush. My bad.
The second mechanic showed me the smaller lines rhat are totally
plugged so I think they are more likely going to find and fix the real issue. I did bring up the blend door angle but there isnt flow through the core, so time will tell.
I want to keep this awesome car so hopefully we can make it right. Appreciate comments.

 

When I lost my heat, I replaced both the aux heater pump and the control valve. I don't know which one fixed the problem, but since they were right next to each other, I just did both. They are located on drivers side behind the wheel well inner liner.

 

Interestingly, the first shop said they tested the aux pump and it was ok. The second shop has not even mentioned it yet. I will have to ask about it again.
Thank you.

 

It is a moderately complex heat system to allow for the 4 zone HVAC systems and also the TDIs with their diesel-powered 'parking heater' option installed, which actually tucks up/attaches inside the left front wheel liner on LHD models anyways, etc., but I digress. Overall, the diagnosing of the no heat issue is just a matter of doing some basic detective work...doing the required system checks and using the diagnostic scan tool effectively to quickly rule out/eliminate most of the possible failure points, as it can activate pumps/solenoids, and also run through all the internal blend doors sequences to ensure everything electrical powered is functional inside that system.

When everything else checks out fine, then that just leaves the big kahuna itself; the heater core, which is a real PITA to R&R. If you have the 4 zone HVAC, then there are two heater cores (one in front, one in the rear, left cargo wall area), so you could have working heat in the rear HVAC system, but none from the front, or vice versa.

IMHO, it's not a matter of if you can get your no heat situation repaired, but rather how much it is going to cost to get to that point, since the first shop pulled an 'Audi Stealer' on you.

FWIW:
Audi service guide says change the coolant every 5yrs using their the long-life coolant type meeting the correct spec, so not based on mileage you drive, but merely the time it's inside the system. Definitely don't add tap water, or even bottled 'drinking' water, etc. as in general water products all have dissolved salts/minerals and/or other contaminants in them that will damage a cooling system internally. Distilled water = evaporated water, which leaves behind any contaminants, so that's why if topping up or refilling this system you always use either the premix 50/50 coolant (good for topping off, not for system refills), or the concentrate version which must be diluted with distilled water. The concentrated jug of antifreeze/coolant is a much, much better value when refilling the system after service or following the use of a coolant system flush product to remove contaminants out the system, etc., which it sounds like will be happening soon.

Also, a DIY maintenance tip is to always cycle your heater on full during the warmer months (like Summer) a couple times for just a few minutes in order to circulate the coolant through the heater core(s) circuits inside the HVAC system, as otherwise it just sits stagnant within that circuit. Same goes for the A/C system to keep all the internal seals lubricated so they won't leak, but on a Q7, if you keep it in 'Auto' mode, that runs the A/C compressor automatically to control humidity in cabin year round, so not so much of an issue there. The heater you have to be intentional about it.

Good luck and remember that most of the time on this car you can source the parts from the OEM manufacturer brand rather than having to pay through the nose for the OE, Audi part #, which is produced for Audi by the OEM company. Example: Bosch makes both the fuel injectors and high pressure fuel pump, and sells them outright. Bosch also packages the same exact parts for Audi to sell as 'OE' parts in dedicated/branded packaging, and stamped with Audi part #/trademark on it, etc. Guess which costs you a lot more $$$ ? Audi doesn't make parts; they just make an insane amount of money selling the 'branded OE' packaged version they jack the prices up on.

 

Excellent advice. It has been About five years/ 60k since a flush. Hopefully this repair will be good for another 5. I did not realize there might be a rear heater core as a separate item. More to investigate.

 

Here is a link to a previous conversation on this topic. Very helpful for me. Note: My VCDS scan didn't reveal anything amiss and all my other door flapper tests, etc worked fine. I know I could test the pump from VCDS but I had no way to actually know if it was working (it was just me and I didn't remove the wheel liner to check the pump after actuation). I figured if I was going to do all the work... might as well just buy the parts and replace while I'm in there.

My biggest challenge was actually the coolant purge after the replacement and ensuring all the air was removed. https://www.audiworld.com/forums/q7-...-cold-3005785/

 

Thank you so much.