Blower Not Producing Hot Air

Hi All,

My first post here! Tried searching first but couldn't find anything super-relevant, and hoping this is the right board for it.

About two months ago, the boot latch on my MK7 TDI failed - at almost exactly the same time (I am sure this is unrelated, but felt it might be worth mentioning), I stopped getting any hot air from the blower.

I took it to two local independents - one specialising in VAG, on not - both who were unable to see anything obviously wrong. On both occasions they plugged it into the diagnostic doodad and there were no fault codes, and the temp dial in the car appeared to register and feed-back correctly. The rad heats up to and sits at about 90c as it should, and it looks like coolant is at the correct level and flowing properly.

The blowers push plenty of air, but the temp dial has no influence on temperature, and it's worth noting that the A/C *does* work correctly.

I've also noticed, on very rare occasions, that I do get a *tiny* bit of 'lukewarm' air from the drivers-side dash between the window and steering wheel, if I have the temp gauge turned to max and the speed on 1 or 2, any higher and it just goes cold.

Has anyone experienced something like this before - or know what I can check next?

Both garages suggested changing the thermostat, likely at a cost of about £160, and with the added annoyance that the part can be one of two, and there's no way to tell until it gets opened up which part it is, so they'll need to strip it one night, find out what part it is and next-day it, and then install it the following day. It's under the inlet manifold, or something?

The alternative is to take it to VW and pay (at least) £110 for diagnostics, just to get a quote for the actual repair.

I'm a computer guy - I'd love to add that I know basically nothing about the mechanical workings of cars... I can change tyres and wiper blades - had a crack at changing headlights once but my hands were too fat.

It's starting to get colder and colder, and with a five-month old it's no longer suitable to just load up on blankets.

Help! Need to know what to do next! Anything I can check? Should I bite the bullet and take it to VW? Or have a go at the thermostat replacement.

Presuming they have checked the coolant for emulsification I Doubt it would be the thermostat as the engine would take forever to get up to temperature but would eventually and you would get warm air. I would check coolant levels to make sure they have actually checked it and not just plugged it in and just scanned it.

Sounds more like one of the flap motors has failed, flap jammed or something associated with it. Can you hear it moving when you move the temperature up/down?

Thanks Finglonga!

I want to reiterate that I'm a complete car-numpty! Coolant is in the large-ish clear spaceship-looking container under the bonnet? If so it's between the max and min lines both cold and fully heated, I did top it up because it was a tiny bit low (about 5mm below min).

Could you elaborate a tiny bit on what I'm looking for when I move the temp up and down? Should the engine be on? Just the electronics turned on?

Let me know and I can report back ASAP.

Thanks again!

To my knowledge (and this may be different because I see you're in Scotland), a faulty thermostat will always trigger the MIL/check engine light, because emissions increase if the engine isn't at normal operating temperature. The other way to tell if it's a faulty thermostat is to take the car out on the freeway ("motorway" to you) and watch the engine temp gauge. If it starts to drop, your thermostat is stuck open; increased cold air flowing over the radiator causes the thermostat to partially close to keep the engine temp optimal.

Sounds like the problem is somewhere in the heater/blower/control unit, but I am by no means an expert with VW.

Hey all -

Finlonga - doesn’t appear to be any sounds or changes in sound when I change the temp dial, engine off or on.
Shane - rad temp is a solid 90c regardless of city speed or even out for a quick -redacted-mph spin on the motorway.

ruu1989 said:

Shane - rad temp is a solid 90c regardless of city speed or even out for a quick -redacted-mph spin on the motorway.

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Assuming it's as chilly in Scotland as it is here in MI, if your T-stat were stuck open, you'd see a noticeable drop in engine temp after a few minutes at high (but still legal because speeding is bad) speed.

@Finglonga Is there any easy way I can confirm 'one of the flap motors has failed, flap jammed or something associated with it' myself? Or - take it to the garage?

ruu, I'm not a Mk7 expert, but all of my other modern cars have an electro-mechanical water valve, usually under the hood near the firewall, that controls whether or not the engine coolant is flowing over the heater core. In most cars their will be a 3/4"-1" coolant hose going to the valve which will have a small electrical connector on it, in older cars they may have been vacuum actuated. But, these valves prevent hot coolant from heating up your heater core when not called for. The heater core is in the dash of your car, if there was no valve the heater core would always be hot, causing heat creep in the car, even with the HVAC off and COOL selected. It would just cause the general area of the dash to get warm, which is not desired. These kinds of valves are easy to check, starting from a fully cool car, start your vehicle and turn on the heater. You will feel the hose at this time (right next to the valve) is cool/cold. As the car warms up, keep checking the hose (next to valve), when your car stabilizes at 90c of course that valve would be fully open (depending on car, the valve may stay closed until a certain coolant temp is reached) by now and the small hose should now be warm/very warm. If the hose is cool, then warm coolant is not flowing, which could be many reasons, including a stuck closed heater valve.

The other thing that could be faulty is the blend door. This door is also electro-mechanical actuated in modern cars, and is a flapper near the heater core that directs blower air over the heater core depending on temp request of temp knob. On many cars (not sure about Mk7) you can remove the cabin air filter and watch this door actuate when operating the HVAC control from warm to cool.
Usually, your car will blow slightly warm air if the damper door is inoperative (and the coolant valve is open) as the heater core heats up the general area of the HVAC workings in the dash.

You may just want to have the car serviced as it may be hiding codes that tell the real story. Maybe some fault that doesn't allow the actuator(s) to function.

ruu1989 said:

@Finglonga Is there any easy way I can confirm 'one of the flap motors has failed, flap jammed or something associated with it' myself? Or - take it to the garage?

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You can hear it sometimes, there is a slight hum of motor of a thud of the flap if you go from max air-con to hot. Try putting temperature to HI and go from Max air-con to Hi a few times to see if it makes any difference.

Hi all,

Thanks for the helpful messages so far, I think I have some progress on this.

First, I’d note that I’ve had absolutely no heat from any vents for around two weeks now.

Using a combination of takemorepills and finglonga’s answers, I had a dig around behind the glovebox (uk model) and found the cabin air filter. I did as advised and continuously swapped back and forth from cold to hot, but didn’t see or hear anything unusual.

However, when I drove home after doing this (was in supermarket car park) I noticed i was back to getting warm (not hot) air out of the driver side dash, tepid out of the centre dash, and lukewarm from passenger side dash.

Does this further point to a faulty blend door - is it possible it isn’t able to open/close fully hence the weakness and variability in the heat?

Is anyone able to provide step-by-step on where I can find this and how to diagnose if it’s faulty? Or should I take this new info to my local independent and ask if they can advise? I’m sort of enjoying this DIY approach, but I’m constantly scared I fix one thing and break two more.

Thanks again!

Take it to a dealer. I don't think you want to tackle replacing a blend door or heater control valve. It's probably the blend door since you don't hear the actuator moving.

If you have Automatic Climatronic a VCDS scan should show a fault if it's a blend door.

Sounds like heater valve is working. The heater valve is likely the only DIY component of our suggestions. If the blend door is inop, I would take it to a dealer. Although I don't know Mk7 cars, 90% of the cars I have done HVAC work on have been difficult to deal with when stuff behind the dash is broken. Cut hands, cursing and sometimes dash removal may be in order.

Just been off the phone with another local independent who have a few contacts at VW and suggested there's an ongoing issue with some of the newer Golfs and Passats (maybe others), where there's aluminium corrosion in the coolant loop, requiring the whole system to be stripped and flushed, radiator, heater core, and all. Needs most of dash disassembled and quoted around £700 for repair. Mentioned there was a tech service bulletin out on the Passats already.

Suspect this is legit - as he did say he wasn't able to take on the work himself at the moment but recommended another company elsewhere in Edinburgh to get it done.

Sigh, will keep y'all posted.

You don't need to "remove most of the dash" to replace the heater core. Price quoted seems very high. If there was that much corrosion the car would overheat. It's relatively easy to tell if the heater core is clogged.

The Fed said:

You don't need to "remove most of the dash" to replace the heater core. Price quoted seems very high. If there was that much corrosion the car would overheat. It's relatively easy to tell if the heater core is clogged.

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Also, the coolant would be obviously discolored, and there would be gunk all up in the reservoir.