A/C recirculation failure

[JayCab]

Hello Forum,

My recirc flap has stopped moving up with the “rec” button, which is annoying because it’s much colder when in recirculation.

So far I’ve taken the glovebox out and tested for vacuum on the tube in response to pressing recirc - which is all good and vac seems strong.

I’ve attached another tube to the vacuum servo and sucked on it manually. Air can be pulled through it, but if I suck it hard enough the flap moves a little bit.
—> I presume this is supposed to be a totally sealed flexible bladder?
—> Unless it’s supposed to pass air as some pressure regulation?

I presume my vac servo has gone and it’s a dash-out job, but thought I’d post in case anyone knows alternative approaches..?

Has anyone successfully changed this as a glovebox out only job?
Is it "just" a dash out job?
Is it a dash out and HVAC out job?

If I am to take the dash out to do this, would I be mad not to change the heater core at the same time?

Has anyone heard of an A/C evaporator going bang or do they last forever being low pressure? In any case the RHD evap is unobtanium now.


Any assistance appreciated..!

Kind Regards,

Joseph

[JayCab]

Images attached.
Looks like I need a “Vacuum unit” 191820677B
They exist as NOS but are £150+ from Lithuania.

Anyone repaired one of these?

The pics of the unit online have two screw mount eyelets, but if you look at the pic from my car with glovebox out, clearly one of the eyelets is free and in the air, so I’m not aure how it’s mounted?

Anyone have any pics of what the left side of the evaporator housing looks like out of the car?

I have a vain hope I could change without pulling the dash if I actually know what I’m reaching for…

[johne]

I would go in through the scuttle and check that the recirculating flap is free and not seized first.

As your photos show the vacuum motor is sandwiched up against the bottom of the L/H A post. IIRC, it only clips/rotates in so it should be possible to remove it by just going in through the glovebox aperture.

That vacuum flap motor was used right across the Audi range in the '80s up until '97 when it was replaced by an electric motor the same as the other flaps. S/H ones ought to be plentiful especially in the US so I'd start my search there on eBay.com for a replacement.

I've checked my photos from when I did the climate conversion article but I don't appear to have one of the LHS. I'll check my Bentley and revert.

I don't believe it should be necessary to take the dash out to replace this but if you do remove the dash which isn't as bad as job as it appears, then yes, you'd be mad not to replace the heater core and the AC evaporator will have to come out as well to give you access to the recirc flap motor. The inverse is possible, ie, remove the central heater unit so as to replace the heater core without disturbing the evaporator and fan motor housing but that doesn't help you here.

The key to a long heater core life is to ensure that when you refit the heater unit you do not leave any pressure on the two heater core pipes as they pass through the bullhead. It's very easy to inadvertently leave the weight of the whole unit hanging on those two pipes if you're not careful. I've got a wooden block between the bottom of my heater unit and the floor taking the weight and preventing the heater mass from dropping down onto those pipes.

The evaporator should last forever for the reason you state and no salt corrosion. What doesn't last forever is the low pressure switch on the side of it which I'd replace whilst you're in there since replacing it on it's own - whilst possible - is a b**tard of a job. The AC low pressure switch is critical to the whole operation of the AC.

[Tractor Dave]

I have an ac airbox spare here if you need something.

[johne]

IMG_7059.jpeg IMG_7060.jpeg

Images from Bentley. Looks like you need to be able to access the single mounting screw to get the vacuum flap motor off.

[JayCab]

Wow. Good diagram. Based on that it’s at least a dash-out job, and quite possibly a HVAC out job too if not possible with partial loosening, wiggling and moving the box without removing it..

…I think I’d have to get a brand new vac unit heater core to make the effort and risk worth it…

…until then I guess I’ll just have to have no recirc…but I will try taking the pollen filter out and checking / lubricating with silicone spray from up above in case that fixes it, but not hopeful if the servo doesn’t hold vacuum…

Thanks for your help chaps!

[JayCab]

I don’t suppose anyone has converted this to an electric servo without major plastic butchery?

...although in all fairness, having said that, this vac unit was 27 years old and still working, and I've owned much younger cars with broken climate control servos.

Anyone else had the 9N Polo "thou shalt burn" experience?

[JayCab]

Update: I just went out to my car to cop another feel under the dash educated by the diagram, and I can feel the screw. It is indeed held in with one screw, with the opposite side left flying. I'll have a go at getting it out with a short stubby screwdriver tomorrow...

I've also felt the circlip holding the variable rod into the unit, which should become removable by feel if I can unscrew the unit and the whole thing pulls down a little

...which thanks to the diagram, we know it should by at least 50mm...

...I'm hopeful again. If I get it out slowly and confidently without having to risk bending anything to snap, I think this might be in the "viable fiddling" territory without taking the dash out.

Amazing how useful good diagrams are when you're working blind...

[JayCab]

I’ve actually got it out, intact, opened it up without breaking it, and found a supplier of new rubber diaphragms for vacuum servos…

https://klimakit.com/product/universal-single-stage-vacuum-actuator-diaphragm/

[Nuvo]

That's a great result, is the replacement diaphragm the deep or shallow type?
edit: It looks to be the deep type based on your photos.

[JayCab]

I bought the larger 33mm "deep" diaphragm from this site;
https://klimakit.com/product/univers...tor-diaphragm/

It fits perfectly. Need a little silicone grease to get it to sit nicely over the lip, before pressing the halves back together...

It's a fiddle replacing it in the car and getting the clip / rod re-engaged correctly without the dash out and without breaking anything, but POSSIBLE with:
- a lot of patience (don’t lose it and snap your ~30 year old HVAC plastics)
- nimble fingers
- using some blu-tack to hold clip and the screw partially in place while assembling

Working A/C re-circulation again!
Good as new. Better than a NOS part as the rubber itself is brand new.

Highly recommend doing this! The A/C is dramatically colder and has about twice the airflow in recirc mode.

I’ve had other cars with smaller cabin filters than this that had much less difference between plain A/C mode and A/C+REC mode. It must be in the HVAC unit design. Either that or they are especially prone to clogging quickly, but I’ve changed mine each year…
…maybe just the way they are…

…if anyone want’s a hand with this I’m happy to help…