Bought car in summer, advert said aircon working fine, muppet me did not check, it did not function. Pump is a Sanden non clutch type, the shear plates are intact and the centre nut on the shaft turns with the pulley when engine running.

 

VCDS showed G65 pressure sensor no comms, sensor had corroded and delaminated, no refrigerant had leaked, swopped for new one and VCDS showed IIRC 4 bar pressure on high side but not rising when engine run, bought manifold guages and they show the same.

 

Next suspect was the pump pressure modulating valve, could have become stuck through misuse, vented refrigerant and removed valve, pump lube oil looked very clean, good sign of no internal pump failure. Freed up valve (if it was even stuck) seemed to work but had no reference, refitted, paid for aircon recharge and still not working.

 

bought and fitted new modulating valve and it did seem to have a more positive "thunk" action, regassed and still no increase in pressure on high side.

 

VCDS shows the modulated voltage to the valve starting at 8.4 volt rising to 14.4 with revs, removed connector and connected old valve (now working like the new one) and it is being actioned by the controller, so its not a wiring problem, using a voltmeter at the same time shows the 12v dropping to around 8volt when the solenoid engaged so I think everything is doing what it should be doing but the pressure is not rising in the second circuit and there is no cooling.

 

The pump just looks to be in so good condition that I dont think it has failed through wear or mechanical failure, each time i try again its the cost of a regas so I cant just remove the valve and blow through the internal passages with an airline, well I can but it will cost and unless I'm fairly confident i am just throwing good money after bad.

 

Any other suggestions, things to try or test?

 

Thanks in advance.

 

 

Forget that, you arn't even in the UK 

 

What is the evaporator temp sensor saying?

 

 

Edited 29 January, 20197 yr by SuperbTWM

12 hours ago, SuperbTWM said:

Forget that, you arn't even in the UK 

 

I dont understand.

12 hours ago, SuperbTWM said:

 

What is the evaporator temp sensor saying?

I did not look, was not aware that it was a parameter but it can not cool if the pressure does not rise in the high pressure circuit.

12 hours ago, SuperbTWM said:

 

 

 

Presumably there aren't any clue-giving 'compressor shut-off' codes in measuring blocks?

A misreading evaporator temp sensor would generate one of those if it was causing the system to believe the evaporator was frozen. 

Not sure what it is I should be looking for Wino, I can deduce now that in measuring blocks there will be one for evap temperature which I will check, I have been checking the voltage and current drawn by the solenoid valve and it is being told to operate, if I remove the connector and couple the spare one externally it operates so to me the system is being commanded to work but the pressure does not rise.

 

Can the wrong control valve be fitted? it would be twice in this case.

With VCDS lite I see the following four fields in MB002 on my Polo : Compressor load, refrigerant pressure, compressor shutoff, and temperature (G263) evaporator.  A shutoff code of 0 means the 'tronics thinks there's no reason to inhibit compressor action.  I think this is what you'll see as otherwise you might not be seeing as much electrical activity at the valve.

Will check later thanks, have always been confused by compressor load and RPM as there is no means of it being measured, the RPM would be a function of engine RPM x the pulley ratios but the load can only mean what loading the system is trying to put on it, in my case there is no load being produced by the pump.

 

I recently downloaded the latest version of VCDS and they have changed the name being used for the valve actuation, cant recall what it is now, also the high side pressure now seems to be guage pressure and not absolute pressure as before, either that or the last recharge is exactly 1 bar less, maybe a temperature thing.

Compressor load might be a calculated value; from current cabin temperature, fan speed, demanded temperature etc. I guess.

 

Funny you should mention gauge versus absolute pressure, because my observations with VCDS lite have made me question what's written by one of the VCDS team on the subject on their forums:

https://forums.ross-tech.com/showthread.php?633-Tis’-the-HVAC-Season/  section: "Added Information (12 July 2016)"  I've asked Dr Peter about it on page 4 but got no answer to date.

 

Handy thread for diagnostics, if you haven't been there?

 

1 hour ago, J.R. said:

 

I dont understand.

I did not look, was not aware that it was a parameter but it can not cool if the pressure does not rise in the high pressure circuit.

 

As per Wino, if the evap sensor is seeing a low temp it will not cut the compressor in  

 

if the ambient temp for example is too low then it will cool it down to the point it will inhibit compressor. 

 

Keep going through the measuring blocks until you find it, you need to check this end of things first rather than starting at the expensive end

 

Edited 30 January, 20197 yr by SuperbTWM

I am with you 100% there SuperbTWM, I am not going to play parts bingo with an expensive compressor and recharge without being sure.

 

Wino, thanks for the link, it will be very usefull, I will now do a function test on the cooling fans, I will have done one in the past while playing but need to do so now.

 

I keep coming back to the fact that the valve seems to be commanded yet the pressure does not rise, its very hard to see the coupling but all the shear plates are intact and looking down with a torch when engine running I can see the shaft nut turning but does that mean the shaft inside and the pump internals are also? Maybe removing some plastic panels might help.

 

I keep wondering if an internal passage is blocked or the control valve is perhaps a shorter version and the o rings are not sealing off the internal passages, if I remove it to check and measure inside even if I could access and see with my old eyes I will lose tha aircon charge again and continue to make a hole in the ozone layer.

Cooling/rad fan(s) operation in the context of A/C is triggered by refrigerant pressure rise, on our cars anyway. Fan speed 1 on at 9 bar, off if it drops below 6.8 bar. Fan speed 2 on at 16 bar, off again at 12 bar IIRC.

Octy 2 onwards may have fan control module within radiator fan package, and continuous speed control I think.

Edited 30 January, 20197 yr by Wino

Been out and had a play, under measuring blocks for the engine controller the only fan that can be tested is cooling fan 1 low speed (I think but have already forgotten due to absence of short term memory (brain damage), it worked OK.

 

Under HVAC controller there is no measuring block for compressor shut off.

 

There was no voltage showing for turbine voltage which I think is the voltage to the control valve although later it showed 4.7v and a corresponding current, sorry I cant recall the details and i am useless with the computer, I would not know how to save and reproduce it, I should have written it down but i can always memorise and recall everything only to have lost it all 3 minutes later.

 

The temperatures may reveal something, there is snow on the ground, evap temp was 2°c and vehicle internal temp was 8°c, climate control set to "LO" so maybe it would not actuate the compressor? However turning it up to heating on "AUTO" did not either.

 

When it was recharged it was in a warm workshop for an hour so the cooling would have worked on "LO" but for whatever the problem is.

3 minutes ago, J.R. said:

Under HVAC controller there is no measuring block for compressor shut off

That's unfortunate, and I can't explain it. Maybe it's called something different in latest versions? Look for a column with any unfathomable title, of numbers in the range 0-19 that don't change much/at all?

AFAIK the air-conditioning only works when ambient temperature is above 4°C. Of course you could maybe trick things temporarily by heating the OAT sensor.

 

At this stage I would say the novelty and self sufficiency aspect has probably long gone and the best course of action would be to pull the pin and take it to an air-conditioning SPECIALIST, not a drive by chain.  Don't give them a clue and let them diagnose and rectify your snag(s).

That might be the case in your country but even just trying to find such a mythical beast in this country would be like climbing Everest and if I were to find one I would have to drop my trousers, lube myself up and bite on a rubber dog chew.

 

The novelty and self sufficiency is still with me and always will be i am proud to say, its an essential survival quality in this country.

 

In 15 years of trying very very hard I have still yet to find a company that can make a replacement sealed unit for a broken window, in the UK I have a choice of 4 small businesses within a 10 mile radius, the one 1/2 a mile away will take my order and have it made for the next day and are happy to store it for a few months till I return and pay.

Wino.

 

Maybe the on/off status is relevant only to compressors with a electro-magnetic clutch? The constant drive ones (cant recall the name) are always on between 0 and 100%.

Nope, both our cars are clutchless.

Shutoff in this context means 'activity inhibited electronically' rather than on/off like with a magnetic clutch.

Someone else with recent/up to date full VCDS will hopefully be along soon to explain where it is to be found (may vary from model to model of car, I guess).  On version 18.2 (I think I saw)  it as column 1 of mvb1 as far as google images can help me. Haven't found anything more recent, but some versions seem to have four columns of it, giving recent history of shutoff, as well as present status.

 

Edited 30 January, 20197 yr by Wino

I dont understand MVB1?

Measuring block 1:

 

 

That's dragged off google image results, no idea what car or vcds version.

Edited 30 January, 20197 yr by Wino

If your evap temp is 2 degrees your compressor won’t be commanded to do anything as it would cause a freeze up. 

 

If you turn the air con off and run the blower does the evap temp come up and match the ambient?

 

 

 

Edited 30 January, 20197 yr by SuperbTWM

Well done Wino!

 

Just been out in the cold again, it was there! Shutdown code 8, evaporator temp less than 3°c

 

Now I know what to look for when things warm up a bit.

 

SuperbTWM, just read your reply, too cold to go out again, not quite sure what you are asking but will probably work it out ny tomorrow for round 2, I imagine the evap (is that the outside radiator?) will be at the same temp as ambient - 2°c, how would using the heater affect it?

 

Or if it is inside the heater unit then the earlier reading of 2° against the internal temp of 8° would be suspect, maybe we are getting to the root cause of the problem, an incorrect evap temp sensor?

 

Let me know if the evap is inside the vehicle and I will put a heater in it overnight.

 

This VCDS is a great tool when you know what it can do!

4 minutes ago, J.R. said:

Well done Wino!

 

Just been out in the cold again, it was there! Shutdown code 8, evaporator temp less than 3°c

 

Now I know what to look for when things warm up a bit.

 

SuperbTWM, just read your reply, too cold to go out again, not quite sure what you are asking but will probably work it out ny tomorrow for round 2, I imagine the evap (is that the outside radiator?) will be at the same temp as ambient - 2°c, how would using the heater affect it?

 

Or if it is inside the heater unit then the earlier reading of 2° against the internal temp of 8° would be suspect, maybe we are getting to the root cause of the problem, an incorrect evap temp sensor?

 

Let me know if the evap is inside the vehicle and I will put a heater in it overnight.

 

This VCDS is a great tool when you know what it can do!

 Are you trying to run the AC in -2?

Plus 2°c, I am trying to run it to diagnose the problem I have had with it not working since I bought the car, today just happens to be very cold!

1 minute ago, J.R. said:

Plus 2°c, I am trying to run it to diagnose the problem I have had with it not working since I bought the car, today just happens to be very cold!

Your wasting your time bud, wait while it gets warmer. 

I am not wasting my time because I am not trying to get the aircon to work at 2°c but to find out why it has not been working at normal temperatures, far from wasting my time thanks to advice on this forum I have learned a lot today and for the first time feel that i may be getting closer to the real problem which looks like it might be the evaporator temperature sensor.

 

I have found now that the evaporator is inside the cabin, part of the heater/climatronic unit, as such it should be at the same temp as the interior vehicle temp and not 6° beneath it, I can understand now what you were asking me about does the temp come up if I use the heater, in fact I am going to brave the cold and start the car and let the heater do its job for an hour before doing another VCDS test.

 

I amjust going outside now, i may be some time........................;