Had A/C re-gassed but still not working

[Alibaba99]

I understand all that, and am not expecting a system capable of -40°C to +30°C in a car, but to be able to go down to -4 maybe -6 outside ambient is perfectly within the systems capability, even without crankcase heaters, and at those temps the refrigerant would still be a gas going to the compressor so no chance of hydraulicing.

The evaporator though is inside the car, and within the main HVAC unit so on a cold morning almost everyone will have the heater on, which will mean hot air (on most modern cars the coolant within the engine rises in temp fairly rapidly once the engine is ruining so hot coolant will be delivered to the HVAC within a few minutes), is being put across the evaporator so there will be minimal chance of icing up surely ?

Yes pressures will drop slightly in those initial couple of minutes, but again I do not see how they will fall enough to make the system inoperable, yes it will be slightly less efficient but pressures will increase quick enough once the heater is warm and the internal ambient has raised a degree or two, it will still be well within the spec of the refrigerant and will not be low enough that liquid will be returning to the compressor.

The air passes over the condenser before it reaches the heater though. And I think you will find that virtually all cars switch the aircon off once ambient is below a certain threshold (on Saabs its 3°c). Once the outside air temperature is below that level it is already normally pretty dry anyway.

 

[Dangerous Dave]

I have managed to locate the outside temperature sensor, and this is the one which informs the trip computer display, and also affects the A/C, as the A/C light would not come on when I unplugged the sensor. It appears this is working completely fine. Is there another sensor located outside the cabin under the front bumper, or is it the cabin air temperature sensor I need to be locating? It's a pain in the arse a it's the newer shape of A3, there haven't yet been enough failures of the system to see any tutorials/videos. It seems parts are difficult to source as well. May well be a breakers yard job I think. If anybody in the Manchester area has access to a VAG-COM scanner I'd be eternally grateful if I could borrow it to narrow down which sensor it is that is failing!

TBH I would just take it to Audi, they do a fixed price diagnostic fee and will tell you where the issue is. I doubt they would charge a lot to replace a temperature sensor either.

 

[ttaskmaster]

It's a pain in the arse a it's the newer shape of A3, there haven't yet been enough failures of the system to see any tutorials/videos.

Does the unit not have a self-test mode like the older Climatronics?#

 

[Entai]

The air passes over the condenser before it reaches the heater though. And I think you will find that virtually all cars switch the aircon off once ambient is below a certain threshold (on Saabs its 3°c). Once the outside air temperature is below that level it is already normally pretty dry anyway.

No because ambient air that comes through to the HVAC unit inside the car, comes in through the scuttle panel inlet and then passes through the pollen filter,into the HVAC, it goes no where near the front of the car where the condenser is.

There is zero technical reason for the AC to be switched off at low ambient.

There is only one reason that I can think of why the AC woudl turn off at low ambient, and that is cost.

It is cheaper for manufacturers to do that.

Same as the regulations have exemptions that allow cars to spill a small amount of refrigerant into the atmosphere over a few months or years.

So no manufacturer builds a completely sealed and tight system.

They could if they wanted to but it would cost more and regulations exempt them from having to build fully tight sealed systems so they don't.

There will always be minute leaks in every single vehicle (unless you are very lucky) and the pretty much every vehicle out there will need re-gassing every few years.

 

[adamtbray]

Does the unit not have a self-test mode like the older Climatronics?#

It possibly does, but I can't find anything online about it as the model is probably too new for anyone to have written about it. I've tried pressing combinations of buttons on the A/C head unit but haven't had any luck.

TBH I would just take it to Audi, they do a fixed price diagnostic fee and will tell you where the issue is. I doubt they would charge a lot to replace a temperature sensor either.

I guess not, but they always seem to find a way to charge two hours of labour at 80 pounds per hour!

 

[Dangerous Dave]

I guess not, but they always seem to find a way to charge two hours of labour at 80 pounds per hour!

They have set time to replace parts that they quote on before the work. You can then haggle around 20% off what they quote. I have generally found them cheaper than specialists due to this, a specialist will have half the hourly rate but quote double or more time to replace the parts.

 

[Alibaba99]

No because ambient air that comes through to the HVAC unit inside the car, comes in through the scuttle panel inlet and then passes through the pollen filter,into the HVAC, it goes no where near the front of the car where the condenser is.

There is zero technical reason for the AC to be switched off at low ambient.

There is only one reason that I can think of why the AC woudl turn off at low ambient, and that is cost.

It is cheaper for manufacturers to do that.

Same as the regulations have exemptions that allow cars to spill a small amount of refrigerant into the atmosphere over a few months or years.

So no manufacturer builds a completely sealed and tight system.

They could if they wanted to but it would cost more and regulations exempt them from having to build fully tight sealed systems so they don't.

There will always be minute leaks in every single vehicle (unless you are very lucky) and the pretty much every vehicle out there will need re-gassing every few years.

Brain isn't working. It passes over the evaporator first and then the heater.

 

[adamtbray]

They have set time to replace parts that they quote on before the work. You can then haggle around 20% off what they quote. I have generally found them cheaper than specialists due to this, a specialist will have half the hourly rate but quote double or more time to replace the parts.

Yes, I agree now I think about it. You know what you're getting into with the dealership, and they'll actually be able to properly diagnose it. I've bit the bullet and booked it in at Audi. Shouldn't be too expensive if all they're doing is replacing one sensor, as you said.

 

[ttaskmaster]

It possibly does, but I can't find anything online about it as the model is probably too new for anyone to have written about it. I've tried pressing combinations of buttons on the A/C head unit but haven't had any luck.

2013?
That's four years old!!
Have you a pic/link to what your interior unit looks like?

 

[adamtbray]

I know, however the only models I can ever find are before this version (pre 2012) https://services.edmunds-media.com/.../a3/2015/lt/2015_audi_a3_det_lt_92115_717.jpg

 

[Entai]

Brain isn't working. It passes over the evaporator first and then the heater.

Yes but they are very close together within the HVAC unit, and the radiant heat from the heater matrix will be plenty enough to keep the evap from icing up.

Also if the system is being used correctly the air that is coming across the evap and heater matrix, should be from the cars cabin and not from outside, as at low outside ambient temps you SHOULD have your climate control/AC on re circulation mode so you are not drawing in cold ambient outside air, you are circulating the air within the cabin and conditioning that air alone.

 

[ttaskmaster]

I know, however the only models I can ever find are before this version (pre 2012)

Audi models seem to like this style of method:

"With ignition on (engine running or not) and climate control on, press upper vent button on driver's side and recirculate button simultaneously. The code # will appear on driver's side temp window and associated value appears in passenger's side temp window. You can scroll through codes 1-149 with "+" or "-" buttons on drivers side"

Make any sense?

 

[RJC]

Yes but they are very close together within the HVAC unit, and the radiant heat from the heater matrix will be plenty enough to keep the evap from icing up.

Also if the system is being used correctly the air that is coming across the evap and heater matrix, should be from the cars cabin and not from outside, as at low outside ambient temps you SHOULD have your climate control/AC on re circulation mode so you are not drawing in cold ambient outside air, you are circulating the air within the cabin and conditioning that air alone.

The other issue is the discharge side, the compressor may not be able to develop enough head pressure as most cars can't control the amount of air onto the condenser when traveling at 30 - 70 mph with low ambient temps and wind chill factor.

 

[Alibaba99]

Yes but they are very close together within the HVAC unit, and the radiant heat from the heater matrix will be plenty enough to keep the evap from icing up.

Also if the system is being used correctly the air that is coming across the evap and heater matrix, should be from the cars cabin and not from outside, as at low outside ambient temps you SHOULD have your climate control/AC on re circulation mode so you are not drawing in cold ambient outside air, you are circulating the air within the cabin and conditioning that air alone.

Recirc should be used for the absolute minimum. Either to prevent sooty nastiness from the car infront or to reduce the interior temperature as rapidly as possible after startup on hot days. The last thing you want to be doing is pulling the damp fuggy air from the cabin back into the car, especially if the aircon has switched off due to the outside temperature and so won't be reducing the moisture content. Why do you think there are so many completely misted up cars on the motorway? They are the ones running recirc and probably aircon off as well.

 

[Entai]

Yes I agree on using re-circulation mode for the bare minimum, but as well as cooling the car rapidly on hot days, it will also heat the car faster on cold mornings.