Wires, HVAC and brake switch oddity

[Nobby]

Wassup chaps.

Had a few busy weeks and managed to knacker my ankle so not had much time to look at the car for a bit.

My air con hasn’t been particularly cold this summer. It’s cool enough to keep you comfortable in 30 degrees but not quite the cold you’d expect on ‘Lo’. I thought i’d Investigate to see what’s what’s and found a few things.

........ just switching to PC as battery is running out.,,,

[Nobby]

So, back now.

Plugged in the old VCDS and had an error on the Fan Module 2. This is the second time thats happened now and I replaced it with a second hand unit last time. Didn't want to spend a huge amount on another one so got another cheap second hand unit, plugged in, same error still. Fan still doesn't go round when air con is on Reckon its either problem with the wiring or controller or both. Seems like a coincidence.

Second problem with HVAC - drivers side seems to be a little warmer (maybe 2-3 degrees warmer) than the other. Again VCDS said an intermittent problem with the drivers side temperature control flap motor. Got busy in the drivers side footwell and oh my god what a pain in the rectillium it is to get at. Once you remove about a million screws you finally get to the flap motor and guess what - its seems to move perfectly. Getting full motion in both directions. Error remains so maybe something else isn't right. Even with flap motor disconnected and manually moving flaps there still a temperature differential. The way the hvac unit works is air flows through the air con condenser and then goes through the heater matrix. The flaps in cold mode block off the air through heater.

With both of these in mind would it make the difference between making the HVAC cold to mega cold? It was regassed last year anyway and there are no leaks. No other errors. Big fan radiator fan works a treat.

Third problem - or maybe more of a question. My rear vents don't really blow a huge amount of air out of them. According to the diagrams they are linked to the middle vents but lack a lot of the airflow. Anyone else's the same. I know there is a lot of ducting in between them so that could be loose etc..

Fourth thing. I managed to break the brake switch as I was in the footwell. All sorted now with a new one, but when it was just the bracket on the switch that was broken. When I gaffered it together temporarily the car drove like a scalded cat. Throttle was very responsive and felt faster. I know you can adjust the brake pedal so the switch engages or not, but does this affect the throttle etc..? The new one slipped in fine, and the brake pedal needs to be pressed about 10mm down to disengage the switch. Assume this is about right as its the same as before.

Fifth thing.... With the drivers side lower dash panel out I found a random wire. I'll post a picture up soon. Its a black twisted pair and seems to run from a box just near to the drivers side end panel. Is it for the alarm? I'm hoping so as my alarm goes off every now and then and I can't find the reason why.

ANy advice welcome.

[bilko1]

Sorry can't help with the HVAC problems but doesn't VCDS tell you what triggers the alarm?

[Nobby]

No - VCDS just says 'Alarm triggered by interior monitoring'. I was hoping that the wire might go so one of the sensors. Given the error it could be either side sensor, or the box which controls both of them thats faulty. I've managed to get some second hand ones but reluctant to swap things over as A - I hate doing interior panel removal and B It might not even be the problem. It also does it when the interior monitoring is turned off via the little button by the drivers seat. Suppose it could also be a CCM fault sporadic error but there is no water ingress and connectors are clean.

I should also add about the HVAC that it seems to be showing good values on the VCDS, but might be worth comparing real time figures with someone else i.e. refrigerant pressure etc.. to make sure the compressor is working ok. Also carried out the HVAC flaps reset which didn't make any difference.

[Shoppinit]

HVAC is voodoo. I can't even connect to mine with the Vagcom except when Mercury is rising in Uranus.

IIRC you can actuate all the flaps and check all the temp sensors and position switches from the Vagcom, so it's probably a question of slogging through it all. I suspect your temp imbalance is just the way it is. Probably nobody at Audi thought anyone would be measuring it.

As for the alarm, you can check the wire colour on Elsa so see if those are the alarm ones. I personally would be tracing them back to see where they go.

[Nobby]

Thats what I thought Shopp

The temperatures seem to be in around 9 or 10 degrees when the outside temperature is at a normal level, but on 30 degree plus its getting to the mid to high teens. Its almost like it can cope ok when its cooler and the hotter it is it struggles to keep the temperatures down. I might try supplying a 12v feed to the smaller fan to see how much of a difference it makes.

The wires did look out of place compared to the normal loom - almost an afterthought during installation. I know alarms aren't often standard so can look like they are cobbled together. There was also a red twisted pair going to I assume one of the 12v switched feeds. More digging required.

[Shoppinit]

How cold is the evaporator getting? Should be nice and frosty.

Might be worth getting the gas done again. You really need someone who knows what they are doing to put the system under vacuum and get all the moisture out. It's amazing how much comes out.

It could be that your filter / dryer is now US. Might be worth replacing it.

I would also put a LED slaved to the compressor relay or compressor to see if the request is getting to the compressor properly. I had an issue with the Saab recently where the relay contacts were burned out so the compressor wasn't coming on properly. Felt like it needed regassing, but once I'd fixed the relay it started blowing ice cold again, even when it was 30+ outside. Noice.

[Nobby]

Haven't really checked but the dryer is cold to the touch and is covered in condensation - not frosty though. Evaporator isn't that easy to get to as you need to remove the glovebox and even then I think you only see the pipes. Might check the drain plugs to make sure nothing it backing up and frosting up the evaporator too much.

It was regassed as a precaution last year (was still working etc..) at an auto electrics place, not just any old garage.

[bilko1]

You mention drain backing up, I had this. It was caused by the flap under the car getting stuck due to the Milltek heating it up.

[Nobby]

Made a couple of checks last night. Applied 12v to the small fan and........ nothing happened. Doesn't seem to be moving at all. Its not seized as I can move it with my hands. The fan controller seems to output 6v permanently, and when the air con is engaged it outputs 10v for about 30 seconds and drops back down to 6v. I wonder if because it knows something is wrong its telling the small fan to be on permanently. The large fan works in a similar way - if there is a fault with the coolant sensor the ECU turns the fan on regardless of the engine temperature.

Anyone remember if the small fan is a fixed speed or 2 stage?

Cheers
Chris

[Shoppinit]

It might be a pcm fan. You'll need a silly scope to check.

[Nobby]

Really? The standard plugs on the control unit has 2 big connectors (assume for 12v/earth feed), another is the cable out to the fan (only 2 smaller and just says +/- on the label) and then an additional plug which has 6 pins, but only 2 that seem to be used. One says diag and another says pin 83 or something. I'm assuming that one is for the error control back to the ECU/CCM, haven't checked what the other pin does yet.

Chris

[Nobby]

Been away for the last 2 weeks and although it’s been 25+ the hvac seems to be pretty cold..... haven’t checked the drain plugs but condensation is pooling under the car.

Got a replacement small fan. Hooked up to a battery and works a treat. Mine must be duff. Gonna hook up the new one to the car tomorrow and see if it works via the controller. Swapping fan over fully needs bumper removing and front section in service position..... <groans>

[Nobby]

New fan plugged into controller, air con turned on and fan works! Now just to find the time to fit it....