Air con Vacumn problem - When under Power..

bdennis · 09-01-2006, 03:22 PM

Hey guys,
Just wondering if anyone has seen this before.
Picture this.. ED XR8 Sprint. - Manual - Stock..
Air con on and with setting set to on face with recirc on.
Under normal conditions works fine (Not towing)..
When towing and under power (maintaining 100km/h - towing a 1200KG Van) the vent direction changes to on the screen and fan speed seems to reduce. When back off the accelerator and glide the vents then return to face and fan speed increases..

Seems to me a vacumn problem. Have checked green and orange Vacumn pipes in engine bay and both are connected fine.

Have seen a similar problem when I accedently knocked the vacumn pipe out of the heater hot water tap in the engine bay.. (Checked it and is ok)

Have not had time to have a flick through the workshop manual..
Any ideas? May be a Vaccumn problem else where...

papaghia · 09-01-2006, 04:26 PM

same thing happens in my EF

its just stock, when i push it hard say over 2500 - 3000rpm and hold it till red line, setting changes

would also like to know what causes this!

is it different pressure in the intake manifold that causes differnt vacumme levels?

i dont know..

bdennis · 10-01-2006, 03:46 PM

looking in the Workshop Manual..
Condition - Air flow changes direction when vehicle is accelerated..
Possible cause:
Vacuum system leak - Check vacuum system with hand vacuum pump from the switch connector, service tubing, or replace damaged components as required.
Faulty Vacuum check valve - replace....

A fat lot of good that is..
Had a bit more of a scan. It looks like the vacuum control valve is only pre EBII.. AHHHH.

bdennis · 10-01-2006, 03:52 PM

more reading..
The Pre EBII Vacuum control valve is on the engine. The EBII (and on) seem to have one near the heater control. It has a black vacuum line to the valve and then a organe one on the other side..

Time to go check all connections

fairmont1998 · 10-01-2006, 05:27 PM

First thing I'd check is the check valve.
It is loss of vacuum causing the actuators to return to the default settings.

bdennis · 10-01-2006, 06:05 PM

Any bright ideas where the check valve is? The manual is not specific? I realise you have a EL but that may give me a clue and prob help JKK.....

NZ · 10-01-2006, 09:35 PM

follow the vac line back to the manifold. there should be a little blue thing about as round as a 5c peiceinline.

the_scotsman · 11-01-2006, 07:02 AM

This is weird, but I had the SAME problem last night!!

I found it to be as the others have said, a vaccuum line.
It was the vaccuum line that goes to the heater tap under the car that had come off...

but I just noticed you checked that too....hmmm....

bdennis · 11-01-2006, 07:59 AM

NZ,
OK will go looking.. It is not a big issue as it was primarily while towing.

Scotsman,
Yes I had this before. I notice that the one that goes into the heater tap is not a real tight fit so it may be leaking there also..

More work to be done....

KEV EB XR8 · 11-01-2006, 08:19 AM

Eb2 v8 i have the same problem at high revs when towing or hard load

hope you find out so i know what to do?

LTDHO · 11-01-2006, 08:20 AM

Have you got an XD or later car? (I know it's and ED)

They all do this underload.

Only fix is either bigger vacc tank or vacc pump.

bdennis · 11-01-2006, 09:31 AM

LTDHO,
Hmm. So form what you are saying, if all do it then I would be chasing my tail... Bugger... Oh well. I only tow on rare occations.. So I wont bother. I may look for the check valve and see. The AUII XR6 did not do it nor did the BA XR6T do it. (Yes they will have newer / different heater / air con units so this must have been fixed...)

naughts · 11-01-2006, 09:37 AM

I've had XF,ED now AU2 - They all do it.