No low speed fans, no AC

[RIAL]

Is it possible that my AC compressor clutch is not kicked in because of a bad rad thermo switch? Have no low speed fans but they R fine because I test them bridging the rad switch connector. Gas and pressures R fine too.
FCM and Climate Control replaced before and I'm guessing the low speed Fan must be a requirement for the AC to work and if the switch is not turning the low speed, them no AC compressor. Does this makes sense?

SeekOff this AC


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[<tuffty/>]

Check fuses on top of the battery... the inside one of the three 30a fuses corrodes and causes this...

http://www.audi-sport.net/xf/threads/my-minor-modding-thread.76389/page-83#post-2617553

<tuffty/>

 

[ayfreetee]

A regas may be required, as lowe gas will stop the clutch from kicking in, although you said the pressure is fine, do you know this for sure?

 

[RIAL]

Check fuses on top of the battery... the inside one of the three 30a fuses corrodes and causes this...

http://www.audi-sport.net/xf/threads/my-minor-modding-thread.76389/page-83#post-2617553

<tuffty/>

Forgot to mention all fuses are fine.
Thanks


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[RIAL]

A regas may be required, as lowe gas will stop the clutch from kicking in, although you said the pressure is fine, do you know this for sure?

Yes.
2 different AC mobs checked and both say everything is fine with the gas and they even could make the compressor to work but something is making it shut down.


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[<tuffty/>]

If the pressure switch was faulty it would most likely have a fault code associated with it... a scan of HVAC with VCDS would be an idea...

Low speed fans come on with the AC so if the AC is not working they will then only come on at around 96/97 degrees.. you won't see this on the dash so you would need to use VCDS (or an app like Torque) to monitor actual coolant temps and see if you have fans regardless of AC...

Pressure switch can be found behind the heatshielding on the bulkhead

<tuffty/>

 

[RIAL]

If the pressure switch was faulty it would most likely have a fault code associated with it... a scan of HVAC with VCDS would be an idea...

Low speed fans come on with the AC so if the AC is not working they will then only come on at around 96/97 degrees.. you won't see this on the dash so you would need to use VCDS (or an app like Torque) to monitor actual coolant temps and see if you have fans regardless of AC...

Pressure switch can be found behind the heatshielding on the bulkhead

<tuffty/>

Tks for your reply.

My question is about the radiator thermo switch on the radiator not the AC gas pressure sensor, like you said behind the heatshiel. That one does not have anything to do with the fans and yes, it would have a fault code.

No fault codes on VCDS and I know the low speed is not coming up because I already waited, with cold engine, for them to start and when they finally started the temp was at 100 and something degrees.

Apparently that radiator switch is only there to turn the low speed on and also send that information to the Fan Control Module then the Control Module is responsible to turn the high speed fans when receives the signal from the coolant sensor.

 

[<tuffty/>]

My question is about the radiator thermo switch on the radiator not the AC gas pressure sensor, like you said behind the heatshiel. That one does not have anything to do with the fans and yes, it would have a fault code.

Actually yes... it does have something to do with the fans... low speed fans operation is triggered both from the thermo switch and AC system so its relevant especially as you say the AC isn't working.

Fans will run at low speed all the time if AC is on... if AC is off (or broken) then low speed will not run until coolant temp hits 96/97 degrees...

If your coolant temps are exceeding this and the fans are still not coming on then its plausible that the thermo switch is faulty...

As you have already tested the fans by unplugging and shorting the thermo switch plug then it suggests the thermo switch is faulty but what you have not appeared to have tested is if the low speed fans kick in when coolant temp is 96+ degrees which will validate if the thermo switch is faulty..

Low speed will still work if AC is off/broken but only when at 96+ degrees... this now needs to be tested

<tuffty/>

 

[RIAL]

Tks for the explanation.

So, if the low speed fans don't get triggered because of a faulty pressure sensor or thermal switch the AC won't be turned on ?

The only time the fans coming on is on high speed and when the coolant temp rich 102 or 104 degrees (this readings are based on Climate Control hidden menu. Just can't remember witch channel).

So far I know that the rad thermo switch needs to be replaced because it's not engaging the low speed before 100 ish degrees .

Question: Could this be enough to do not have AC?

Tks

 

[badger5]

the fan control module turns on the fans from command... The command from ecu/ac, and over ridden by the fan switch

 

[RIAL]

the fan control module turns on the fans from command... The command from ecu/ac, and over ridden by the fan switch

Sorry
I'm confused. What your trying to say?

 

[<tuffty/>]

Air con self study PDF
http://www.volkspage.net/technik/ssp/ssp/SSP_208_d2.pdf

Explains the aircon system and how it uses the fans... AC not switching in could be faulty pressure sensor and/or fan control unit

Fans not coming on low speed at 96 deg and only triggering high speed at 100+ is most likely the thermo switch... replace this first as these are a common failure point...

Coolant system self study PDF...
http://www.volkspage.net/technik/ssp/ssp/SSP_222.pdf

The above is a more general approach on VAG cars I believe but principles are the same

<tuffty/>

 

[RIAL]

Cheers mate.
Great info. Guess I'm changing thermo switch and pressure sensor and see how it goes.

Tks

 

[<tuffty/>]

Cheers mate.
Great info. Guess I'm changing thermo switch and pressure sensor and see how it goes.

Tks

Pressure sensor should show a fault code in HVACS module if faulty... scan with VCDS

<tuffty/>

 

[RIAL]

Pressure sensor should show a fault code in HVACS module if faulty... scan with VCDS

<tuffty/>

Scanned many times with VCDS and nothing.
Meaning that it's not faulty?

 

[<tuffty/>]

Scanned many times with VCDS and nothing.
Meaning that it's not faulty?

I would change the fan switch first... make sure the fans are working.... if there are no fault codes recorded then not sure what else to check but this may give you a head start

http://workshop-manuals.com/audi/a3..._air_conditioner_(in_the_engine_compartment)/

<tuffty/>

 

[RIAL]

I would change the fan switch first... make sure the fans are working.... if there are no fault codes recorded then not sure what else to check but this may give you a head start

http://workshop-manuals.com/audi/a3..._air_conditioner_(in_the_engine_compartment)/

<tuffty/>

Tks for that.
Next week will change the switch then let U know how did it go.

 

[Bradderz_1988]

Ive just had issues till i read this the other day

Basically my car would overheat in traffic monitored it and HVAC was rising to 115'c but still showing 90 on clocks, so i had a look into it found both fans werent coming on even with the A/C switched on, found the 30 amp fuse and the socket had melted at one pin causing the fuse to have plastic on one fuse leg not allowing a good contact, pulled it out and replaced it, fans now working and the HVAC unit doesnt go over 99'c.

 

[RIAL]

Can someone tell me if this makes sense because it doesn't make must sense for me.

So, my AC is not working for a long time and everything was pretty much checked until I found on one of the engine measuring blocks, Compressor OFF: Shut-Off requested by Engine Control.

Today o took the to Audi dealer for a AC diagnose.
Just received a phone call saying that the engine hose breather and crankcase hose breather need to be replaced.
WTF???!??! Is this reason for AC compressor Off???

Also can some one show me this hoses? Tks

 

[<tuffty/>]

Pipes essentially look like this...

All PCV pipes etc are prone to splitting and breaking due to oil and a common failure point...

As for it affecting you AC then no... this won't have anything to do with that not working...

While I'd like to say its Audi rubbing their hands together and the thought of a huge parts list they could put together for an old car this stuff fails all the time and its something I often find myself pointing out on cars that come into Bills..

The plastic pipe on the right of that pic that goes to the cam cover 'triple' hose often breaks from degradation by oil... its about 35-40 from a dealer!... did I mention its plastic? VAG prices on odd things like this are mad sometimes..

<tuffty/>

 

[RIAL]

Tks tuffy

Later I went there and they told me that the ECU is turning the compressor off because of the engine is running rich and that's why they diagnose changing this hoses.
Now somehow it makes some sense. I think

 

[<tuffty/>]

Split pipes cause air and boost leaks which in turn can cause rich running... not entirely convinced of their diagnosis on that tbh as the ECU adapts but replacing split pipes is still a good thing to do regardless...

If the PCV splits its more likely to run lean than rich on idle... it could run rich on boost if the airleak is big enough but if your car is an AMK/BAM S3 or AUM A3 then wideband will adapt for this so again not entirely convinced...

I don't know of an ECU strategy that turns off the AC when running rich... its normally when ambient is 5 degrees or less, faulty fan controller, faulty compressor, AC pressure switch or the fuses on the battery...

<tuffty/>

 

[RIAL]

It's a BAM

Also found this on factory manual. Just to confuse even more because doesn't mention anything abou engine emissions

 

[<tuffty/>]

I had to replace the compressor on my A2 as it had been left to run dry for too long by the previous owner... had a leak from the condenser which I replaced and obviously re-gassed the system but still wouldn't operate AC until I replaced the compressor...

No fault codes from memory either...

<tuffty/>

 

[RIAL]

I have no faults on mine.
I believe that the ECM is actually shutting the compressor of because everything else like pressures, compressor, control module, and pretty much all the AC system were checked by 3 diferentes shops and today Audi also confirmed that it's all fine there.
Has to be the ECM!
What's causing it, it's the big mystery

Maybe the ECM think I'm in 1 gear all the time

 

[RIAL]

Took the car to Audi dealership and they started by diagnosing engine breather hoses as cause for the AC not working. Didn't make much sense to me but they were replaced anyway.
Result: nothing changed. AC still not working

They're second diagnosis is that the ECU remap done is the cause for the compressor shutdown by the ECU condition.

Does this make any sense for you?
They confirmed that the AC system is working fine and the ECU is the last box to tick.

I also found somewhere on the web that Just found on the web that on some VAG cars the Throttle Body Alignmen (Basic Setting) will do the trick!???

 

[S3 Hilife]

They're second diagnosis is that the ECU remap done is the cause for the compressor shutdown by the ECU condition.

It's not like Audi to blame an aftermarket remap LOL

I wonder what diagnostics were carried out to come to that conclusion




Steve

 

[RIAL]

It's not like Audi to blame an aftermarket remap LOL

I wonder what diagnostics were carried out to come to that conclusion




Steve

Yes. Typical "not my problem now "

I guess they come up with this conclusion because on one of the engine measuring locks (group2, I think) is showing condition
12 - Compressor off (request from the engine control unit, via data bus.)

 

[RIAL]

Fixed!!!
I looked property the wiring schematics and there is this wire from the ECU telling the AC unit to shutoff the compressor (- then 5v turn off / + then 5V all good)
Basically I canceled that wire from the connector (back of the AC unit) and run a wire from the cable that powers the AC unit. That way the AC unit have 12v on that pin (+ the 5V, no compressor shutoff from the ECU)