A3 07 Sline not blowing hot air and temp gauge incorrect

[Klinker]

Hiya

Hoping to get some advice about things I don't understand ...

My A3 has stopped blowing hot air and the temp gauge is mostly sat at 50. Took it to my brother who had a quick play and found that when he disconnected the fan, the temp gauge corrected itself immediately and heaters got hot.

He told me it was a broken switch and sent me off to get a new one. However, it seems that these switches don't exist. Did some searching online, couldn't find one for the 170bhp model. Phoned an Audi parts specialist and they said the switch is built on to the fan. So before i spend £250+ on a new fan, wanted to check that it sounds like the right diagnosis? I read a few bits and pieces and not come across a problem with the fans so far - it's been other reasons and this will be the first time he's worked on a car that doesn't have a separate switch. There is also a chance that when I phoned the parts specialist, I asked for the wrong thing? haha!

Thanks in advance

[paintman]

I suspect that whatever it is that operates the switch based on the coolant temperature is faulty & your fan is running continuously.
Usually a coolant temperature sensor which is in contact with the coolant.
I'd suggest you stop your brother fking about with it & get a diagnostic done or at least someone that knows what they're on about.

[Oscar011]

Klinker said:

Hiya

Hoping to get some advice about things I don't understand ...

My A3 has stopped blowing hot air and the temp gauge is mostly sat at 50. Took it to my brother who had a quick play and found that when he disconnected the fan, the temp gauge corrected itself immediately and heaters got hot.

He told me it was a broken switch and sent me off to get a new one. However, it seems that these switches don't exist. Did some searching online, couldn't find one for the 170bhp model. Phoned an Audi parts specialist and they said the switch is built on to the fan. So before i spend £250+ on a new fan, wanted to check that it sounds like the right diagnosis? I read a few bits and pieces and not come across a problem with the fans so far - it's been other reasons and this will be the first time he's worked on a car that doesn't have a separate switch. There is also a chance that when I phoned the parts specialist, I asked for the wrong thing? haha!

Thanks in advance

Get the car scanned. I’ve had something similar and it was the engine temperature sensor just like paintman has said.

[Klinker]

are you always that rude? or is it a special persona that you have created for the internet?

the last time I had a diagnostics done by a garage - they told me it showed an "air con fault that was nothing to worry about" the fault code that showed up is 'fan for interior temperature sensor', which doesn't correspond to the problem i'm having.

Thanks for the replies anyway.

[Mignon]

If the fan switch was broken the fan wouldn't come on. The fan is on all the time because the temperature sensor is broken and is telling the fan the engine is hot when it's really cold. The engine can never heat up properly because the fan is stuck on all the time hence the lack of hot air from the heater.

Not the smartest set of deductions from symptoms back to cause I've ever seen.

[GreenV8S]

Mignon said:

The engine can never heat up properly because the fan is stuck on all the time hence the lack of hot air from the heater.

What's stopping the engine from warming up? The stat ought to be closed until the engine is up to temperature, so the fan is just blowing air over the outside of the engine, which seems unlikely to prevent the engine warming up unless it is in Siberia. I understand that some stats have an electrical override (a heating element in the wax canister) to bias the stat opening temperature. I suppose if this engine has something like that and if it was being powered while the engine was cold it might make it over-cool. Or perhaps the stat has simply failed and is stuck partly open. Either way, it seems to me there must be more going on than just the cooling fan running.

[Mignon]

GreenV8S said:

What's stopping the engine from warming up? The stat ought to be closed until the engine is up to temperature, so the fan is just blowing air over the outside of the engine, which seems unlikely to prevent the engine warming up unless it is in Siberia. I understand that some stats have an electrical override (a heating element in the wax canister) to bias the stat opening temperature. I suppose if this engine has something like that and if it was being powered while the engine was cold it might make it over-cool. Or perhaps the stat has simply failed and is stuck partly open. Either way, it seems to me there must be more going on than just the cooling fan running.

Good points but we are told that if the fan is disconnected then the engine does heat up and the heater does blow hot air. I'm not going to speculate too much about that until at least the fan works properly and the OP can then decide if there is a further warming up problem which may indeed be thermostat related.

I'm also aware that if the thermostat was the sole driver of engine temperature then the fan and radiator shouldn't even be factors until the stat has opened but nonetheless in cold weather it used to be not uncommon to have to mask the rad off to get the engine hot on some vehicles. Thermostats do have some bypass flow built in and maybe this is sufficient to keep the OP's engine cold with the fan on.

[underwhelmist]

Klinker said:

are you always that rude?

Eh? It sounded like reasonable advice to me.

[paintman]

Frequently.
No.

Get your brother to show you on the car the item he says is faulty.
Take the car to your nearest Audi franchised dealer.
Ask one of the parts dept staff to come out to the car.
Point out to them the item that your brother says is the problem.
Get them to give you the price of the item and more importantly its part number.
Now you know what the part is check to see if you can buy it elsewhere cheaper - some parts will be dealer only & you will get no discount, I'm trade & many dealer only parts I only get 10%. Some pattern parts are crap & you're best buying genuine from the dealer.
Buy the part & get your brother to fit it.

Edited by paintman on Tuesday 13th November 10:08

[Mr2Mike]

Klinker said:

Hiya
Took it to my brother who had a quick play and found that when he disconnected the fan, the temp gauge corrected itself immediately and heaters got hot.

Do you literally mean the second the fan was unplugged the temperature gauge went up, or did the temperature slowly rise up to normal some minutes later? I'm not being pedantic, if the temperature gauge responded instantly it suggests there may be a wiring fault.

Are you certain the fan that was running wasn't for the aircon condensor, i.e. was the aircon completely switched off when your brother looked at it? The the temperature gauge only rose slowly after the fan was disconncted, and the aircon was driving the fan then you may simply have a bad thermostat, they invariably stick open and especially on a diesel in cold weather will stop the engine heating up.