Bad Ambient Temperature Sensor? Where's it located?

[kmad86]

Ok, so where I live it's recently been very hot. About two months ago I had my compressor replaced and my ac worked for a little while. There's no leak, but when it gets over 93 outside (actually been around 105 every day here) my car ac doesn't work at all and I am pretty sure the radiator fan isn't working during that time either.

Now my temperature sensor is nearly always incorrect. It's about 15 degrees off when it's really hot. When it's cool, it's not too far off.

Would this be causing me this trouble? Also, I don't have a windows computer to install the service manual so could somebody tell me the location of the sensor? I'm thinking about swapping it to see if it makes a difference.

[mec]

It's right in front of the radiator. attached to the power steering cooler.

[kmad86]

It's right in front of the radiator. attached to the power steering cooler.

I'm not right with the car at the moment, but any idea if I have to take the bumper off or not?

[DRAKLORE]

If you have factory stuff more than likely.
Unless you can somehow drop your plastic skid crap and squeeze you hand in there.
My bumper is Convienently 50% not there so I forget how it's supposed to be lol

[kmad86]

If you have factory stuff more than likely.
Unless you can somehow drop your plastic skid crap and squeeze you hand in there.
My bumper is Convienently 50% not there so I forget how it's supposed to be lol

Have you guys heard of a bad ambient sensor causing this problem. I'm sure it's more than this but hope it's this easy and cheap of a fix.

[DRAKLORE]

Idk, I replaced mine it was
Like 20$

Sorry I didn't read your post

[mec]

Never heard of that, I don't think you can get in there without removing the bumper because of the bumper has an underside. It's right behind the grille, under the crashbar.

[kmad86]

Never heard of that, I don't think you can get in there without removing the bumper because of the bumper has an underside. It's right behind the grille, under the crashbar.

Today it's 85 degrees outside and my temp is pretty close to being accurate in the car. My AC works fine. I still haven't replaced the sensor. I figure I might swap it out, but does the sensor really do more than just read the outside air?

[Charles.waite]

Today it's 85 degrees outside and my temp is pretty close to being accurate in the car. My AC works fine. I still haven't replaced the sensor. I figure I might swap it out, but does the sensor really do more than just read the outside air?

no. But the ECU uses the ambient temp info to calculate A/C load or something.

[airbornerifleman]

no. But the ECU uses the ambient temp info to calculate A/C load or something.

Where are you getting this info? I would like to be more educated on our "AUTO HVAC" system. Please provide link to resource.

[ECS Tuning-Audi]

The ambient air temp sensor does have an affect on the AC, so this could be part of why your AC isn't as cold. You could also be low on R134A refrigerant. There's quite a few possibilities actually, i usually leave AC issues up to the pros.

So some searching around on this site and you might be able to find more info.

Jason

[bman005]

Today it's 85 degrees outside and my temp is pretty close to being accurate in the car. My AC works fine. I still haven't replaced the sensor. I figure I might swap it out, but does the sensor really do more than just read the outside air?

The ambient air temp sensor sends temp signal to the ac control unit and the instrument cluster. If temp is too cold (below 40 F) it will not engage the compressor.

I'd be more interested in why your fan isn't coming on. Fan not coming on = Pressure raising too high too quickly = A/C operation being shut off due to the pressure increase. If you have (or have access to) VagCom I would check the A/C system for DTCs and also when the A/C is not working check the compressor off code in Measured Value Block 1. the code will be 0-18. 0 is compressor commanded on and the others are all different reasons for the compressor not engaging

[fly300kts]

Might have found the root cause of our issues with AC shutting OFF at iddle
Do you recognize this guy?



The A4 does not use an expansion valve like almost every other vehicle. This filter is located inside the pressure hose and even if slighly clogged, the pressure will rise and AC will shut off.
I will probably have time to replace it this WE and will post a DIY with filter location. I will also replace the dryier at the same time.

Phil

[DRAKLORE]

There's no expansion valve? Than how does the system work

[fly300kts]

There's no expansion valve? Than how does the system work

Nope, none
Everything is regulated by this tinny filter who has some kind of brass tube inside

Phil

[DRAKLORE]

Well the filter I have seen on a few 2010 edges, but there was still an expansion valve

[fly300kts]

Well the filter I have seen on a few 2010 edges, but there was still an expansion valve

Check ETKA, no expansion valve on the entire system

Phil

[bman005]

There's no expansion valve? Than how does the system work

Its an orifice tube. When combined with an accumulator it does the same thing as an expansion valve. Expansion systems also have a receiver drier which orifice systems don't

If you go back to the 80's you'll find almost exclusively orifice tubes on Fords. Escorts used to have 2 tools for removing them, the second 1 for removing it after you broke it with the first tool

[DRAKLORE]

So all those expansion valves I replaced were really just orifice tubes?
The lies, the humanity!

[bman005]

So all those expansion valves I replaced were really just orifice tubes?
The lies, the humanity!

Haha, for the record the labor time guide still calls the orifice tube an expansion unit. And I don't want to rain on Phil's parade but I don't think it'll fix the poor cooling at idle, I already replaced mine since it was dirty and it made only a negligible difference. I'm gonna replace the accumulator since I already have the front end ripped off my car while I wait for my couplers to show up. I'll post up in here if it makes a difference

[kmad86]

Might have found the root cause of our issues with AC shutting OFF at iddle
Do you recognize this guy?



The A4 does not use an expansion valve like almost every other vehicle. This filter is located inside the pressure hose and even if slighly clogged, the pressure will rise and AC will shut off.
I will probably have time to replace it this WE and will post a DIY with filter location. I will also replace the dryier at the same time.

Phil

Is this something I can check without changing any fluids or recharging anything?

[kmad86]

I have a VagCom but I plug it up and it doesn't pull any codes. To be honest, it was given to me and I might not even be using it right. I go to the only real mode you can go to in the VagCom and hit enter and it searches but never finds anything.

My traction light always stays lit too like it's not working. I figured it would pull something.

[bman005]

Is this something I can check without changing any fluids or recharging anything?

No, you to discharge the system open up the line and remove it to inspect. Then vacuum and recharge the system

[fly300kts]

Haha, for the record the labor time guide still calls the orifice tube an expansion unit. And I don't want to rain on Phil's parade but I don't think it'll fix the poor cooling at idle, I already replaced mine since it was dirty and it made only a negligible difference. I'm gonna replace the accumulator since I already have the front end ripped off my car while I wait for my couplers to show up. I'll post up in here if it makes a difference

The A4 has a pretty basic system



Compressor
Dryer
Evaporator
Condenser
Orifice tube (#8)

With all the different satellite systems being OK, thinking of fan relays for example making sure that both fans are running full speed when full cold is selected, and of course a system correctly charged, I only see the orifice tube being the root cause

Phil

[bman005]

That was the same conclusion I came to as well. However it did not fix mine, A/C still sucks at idle

[Audibot]

I know my ambient temperature readings increased when I went FMIC, but I think it's the summer heat radiating off of the intercooler doing it. Was worse when I had a poorly shielded intake as well, which is another reason back to stock

[airbornerifleman]

The ambient air temp sensor sends temp signal to the ac control unit and the instrument cluster. If temp is too cold (below 40 F) it will not engage the compressor.

Interesting. So in the fall and winter, when I use my heater and have my system set to AUTO the compressor in not engaged? Does it engage in the winter when I press the defog button?

[ECS Tuning-Audi]

Interesting. So in the fall and winter, when I use my heater and have my system set to AUTO the compressor in not engaged? Does it engage in the winter when I press the defog button?

It shouldn't. In the winter time it wouldn't do any good to engaged the compressor to blow cold air to defrost a window. You'd want heat on.


Jason

[fly300kts]

No flight scheduled this morning so I did the replacement
Shop was busy this morning



Connected the AC cart to recover the Freon



Here is the area where the orifice tube is located



I pulled off the air filter assembly to access the dryer



24 & 22mm wrenches to crack open the line. With small pliers, pull of the orifice tube



The orifice tube is really nasty and I would guess 70% obstructed



Replaced the dryer, reserviced with 780 grams of new Freon. Feels cooler already especially at idle.

Will keep you posted

Phil

[bman005]

Nice! I ordered a new dryer yesterday, hope it takes care of my issue as well

[Charles.waite]

Phil - I presume when replacing the orifice tube you're opening the system right? So I would have to get it evacuated then refilled after replacing it right? And because the system is getting opened up, you'd have to replace the dryer as well.

How many miles did your tube have on it? The A/C in my B7 is a bit warmer than my b6 so I'm wondering if the orifice tube could be blocked or possibly I could be a bit low on Freon. How much would a shop charge to do a pressure test?

[fly300kts]

Phil - I presume when replacing the orifice tube you're opening the system right? So I would have to get it evacuated then refilled after replacing it right? And because the system is getting opened up, you'd have to replace the dryer as well.

How many miles did your tube have on it? The A/C in my B7 is a bit warmer than my b6 so I'm wondering if the orifice tube could be blocked or possibly I could be a bit low on Freon. How much would a shop charge to do a pressure test?

I presume when replacing the orifice tube you're opening the system right? YES
So I would have to get it evacuated then refilled after replacing it right? YES
And because the system is getting opened up, you'd have to replace the dryer as well. Not really. When a system is opened, and if the ambient air is really humid, you just need to vaccum a bit longer (I did 40 mn). My driyer was just old
How many miles did your tube have on it? Car is 2005.5 and 120K miles
How much would a shop charge to do a pressure test? Beauty of my work, it's all free since the shop is almost my office. I guess a full tune should cost around $80 in labor but I am not sure

Phil

[Charles.waite]

I presume when replacing the orifice tube you're opening the system right? YES
So I would have to get it evacuated then refilled after replacing it right? YES
And because the system is getting opened up, you'd have to replace the dryer as well. Not really. When a system is opened, and if the ambient air is really humid, you just need to vaccum a bit longer (I did 40 mn). My driyer was just old
How many miles did your tube have on it? Car is 2005.5 and 120K miles
How much would a shop charge to do a pressure test? Beauty of my work, it's all free since the shop is almost my office. I guess a full tune should cost around $80 in labor but I am not sure

Phil

Thanks!

And I'm quite jealous of your "office"! Maybe I'll have a shop evacuate the AC system and replace my orifice (love saying that word, haha). then have them fill her up. Seattle is quite dry so humidity shouldn't be an issue. Might just replace both though as mines a 2006. Might as well replace it while the system is evacuated...

[fly300kts]

Thanks!

And I'm quite jealous of your "office"!

You are welcome to visit :)

Phil

[lesurfman]

Phil, how does your A/C performs after the surgery?

[fly300kts]

Phil, how does your A/C performs after the surgery?

106F in Florida today and a lot of stop and go all day. Works like a champ. Did not shut off once.

Phil

[cosmicvision]

Hate to be the guy reviving the old thread, but the information here is good & I think I may be up against a similar issue. With the advent of summertime & AC usage, I've noticed the following patterns:

-AC works great & blows cold when the ambient temp on the dash reads a warm temperature (basically whenever the little snowflake isn't there)
-AC blows kind of cold when the snowflake is there
-AC doesn't blow cold air at all when it sinks so low that the snowflake disappears (it will dip way low & bottom out as low as ~50 below, but never goes above where it should be)

With this behavior I can vouch that the ECU does use the ambient temp info to calculate A/C load. Based on other reading I've done, these symptoms seems to indicate a failing ambient temp sensor (the little thing on the front of the radiator if I'm not mistaken?) but the clogged orifice tube seems like it may play into it as well. The indicated temp on my dash rarely stays where it should, and is perpetually going up & down as I drive. And my AC function depends on wherever it sits. I go back & forth between rolling the windows down when it dips low & the AC gets warm, and rolling em back up when it kicks in & blows cold. It's a pretty weird system and complicated to explain to any passenger when they notice me constantly doing the windows-up-windows-down jive.

It's like the car is trying to outsmart me..."It's 20 below outside, why in the world are you running the AC you dummy". But you are mistaken, car!! I'm burning up & you won't give me my cooling relief. Can anybody shed some light on a possible correlation between this topic and the issue I'm experiencing?

[cosmicvision]

Well shoot.............just noticed this is on the B7 forum. Entirely different platform than mine. Will post in the right place now.

[fly300kts]

Hate to be the guy reviving the old thread, but the information here is good & I think I may be up against a similar issue. With the advent of summertime & AC usage, I've noticed the following patterns:

-AC works great & blows cold when the ambient temp on the dash reads a warm temperature (basically whenever the little snowflake isn't there)
-AC blows kind of cold when the snowflake is there
-AC doesn't blow cold air at all when it sinks so low that the snowflake disappears (it will dip way low & bottom out as low as ~50 below, but never goes above where it should be)

With this behavior I can vouch that the ECU does use the ambient temp info to calculate A/C load. Based on other reading I've done, these symptoms seems to indicate a failing ambient temp sensor (the little thing on the front of the radiator if I'm not mistaken?) but the clogged orifice tube seems like it may play into it as well. The indicated temp on my dash rarely stays where it should, and is perpetually going up & down as I drive. And my AC function depends on wherever it sits. I go back & forth between rolling the windows down when it dips low & the AC gets warm, and rolling em back up when it kicks in & blows cold. It's a pretty weird system and complicated to explain to any passenger when they notice me constantly doing the windows-up-windows-down jive.

It's like the car is trying to outsmart me..."It's 20 below outside, why in the world are you running the AC you dummy". But you are mistaken, car!! I'm burning up & you won't give me my cooling relief. Can anybody shed some light on a possible correlation between this topic and the issue I'm experiencing?

What do you mean by "snow flake"?

Phil

[jimrobbington]

What do you mean by "snow flake"?

Phil

On the color display, you get a snow flake on the dash to warn you when the temperature is below ~40°, there could be ice. You might not know this since you live in Florida. Lol.