Hi,

 

I have an Octavia MkII Estate, that has been sat doing not much over the lockdown period, and now I need to use it again the Aircon is not working.

 

There are no errors from the HVAC system in VCDS, there is gas, and it does build some pressure (4 bar -> 6-8 bar), but what ever I do, all I get is hot air from the blower.

 

I've done a couple of VCDS reads, and was wondering if anyone might have an idea what is going on with it?

 

The first read was after it had been sat in the car park all day, so should be steady state. the second is 5 minutes later, with the engine running and the AC turned on.

 

If anyone has any ideas of what might be up, or a good option to investigate, I would love it get your feedback.

 

Many Thanks

James

 

                Address 08: Auto HVAC  (1Z0 907 044 R)	                Address 08: Auto HVAC  (1Z0 907 044 R)
	
18:05:00 Group 001: General	18:11:05 Group 001: General
  6.0  Compressor Shut-Off Code	  0.0  Compressor Shut-Off Code
  800 /min  Engine Speed 	  800 /min  Engine Speed 
  0.0 km/h  Vehicle Speed 	  0.0 km/h  Vehicle Speed 
  04:00  Standing Time 	  04:00  Standing Time 
	
18:05:00 Group 002: Compressor	18:11:05 Group 002: Compressor
  0.010 A  Compressor Current (actual)	  0.820 A  Compressor Current (actual)
  0.000 A  Compressor Current (specified)	  0.820 A  Compressor Current (specified)
  0 /min  Compressor Rotations	  1000 /min  Compressor Rotations
  0.0 Nm  Compressor Load 	  1.9 Nm  Compressor Load 
	
18:05:00 Group 003	18:11:05 Group 003
  4.0 bar  Refrigerant Pressure	  6.0 bar  Refrigerant Pressure
  9.6 %  Radiator Fan Activation (actual)	  9.6 %  Radiator Fan Activation (actual)
  0.0 %  Radiator Fan Activation (spec.)	  0.0 %  Radiator Fan Activation (spec.)
  OFF  Engine Speed (increase)	  ON  Engine Speed (increase)
	
18:05:54 Group 004: Temperatures	18:11:11 Group 004: Temperatures
  34.0°C  Outside Temp. Unfiltered	  34.0°C  Outside Temp. Unfiltered
  34.5°C  Outside Temp. Regulation	  34.0°C  Outside Temp. Regulation
   -  Fresh Air Intake Temperature	   -  Fresh Air Intake Temperature
  45.0°C  Coolant Temperature	  59.0°C  Coolant Temperature
	
18:05:54 Group 005: Outlet/Footwell Blower Temperature	18:11:11 Group 005: Outlet/Footwell Blower Temperature
  35.0°C  Left Outlet Blower Temperature	  39.0°C  Left Outlet Blower Temperature
  35.0°C  Right Outlet Blower Temperature	  37.0°C  Right Outlet Blower Temperature
  41.0°C  Left Footwell Blower Temp.	  39.0°C  Left Footwell Blower Temp.
  40.0°C  Right Footwell Blower Temp.	  38.0°C  Right Footwell Blower Temp.
	
18:05:54 Group 006	18:11:11 Group 006
  37.0°C  Evaporator Temperature	  38.0°C  Evaporator Temperature
  38.0°C  Interior Temperature	  37.0°C  Interior Temperature
  0.0  Left Sunlight Intensity (G107)	  170.0  Left Sunlight Intensity (G107)
  50.0  Right Sunlight Intensity (G134)	  290.0  Right Sunlight Intensity (G134)
	
18:06:00 Group 007	18:11:17 Group 007
     Turbine Voltage (actual)	     Turbine Voltage (actual)
  3.80 V  Turbine Voltage (specified)	  4.60 V  Turbine Voltage (specified)
  8.4 %  Turbine Load 	  16.8 %  Turbine Load 
  14.30 V  Voltage (Terminal 30)	  14.30 V  Voltage (Terminal 30)
	
18:06:08 Group 011: Air Recirculation Flap Control Motor (V113) / Potentiometer (G143)	18:11:23 Group 011: Air Recirculation Flap Control Motor (V113) / Potentiometer (G143)
     Potentiom. (G143) Current Value	     Potentiom. (G143) Current Value
     Potentiom. (G143) Specified Value	     Potentiom. (G143) Specified Value
     Min. Position (G143) (Lower Stop/Close)	     Min. Position (G143) (Lower Stop/Close)
     Max. Position (G143) (Upper Stop/Open)	     Max. Position (G143) (Upper Stop/Open)
	
18:06:08 Group 012: Left Temperature Flap Control Motor (V158) / Potentiometer (G220)	18:11:23 Group 012: Left Temperature Flap Control Motor (V158) / Potentiometer (G220)
  28.0  Potentiom. (G220) Current Value	  29.0  Potentiom. (G220) Current Value
  29.0  Potentiom. (G220) Specified Value	  29.0  Potentiom. (G220) Specified Value
  29.0  Min. Position (G220) (Lower Stop/Close)	  29.0  Min. Position (G220) (Lower Stop/Close)
  220.0  Max. Position (G220) (Upper Stop/Open)	  220.0  Max. Position (G220) (Upper Stop/Open)
	
18:06:17 Group 013: Right Temperature Flap Control Motor (V159) / Potentiometer (G221)	18:11:30 Group 013: Right Temperature Flap Control Motor (V159) / Potentiometer (G221)
  32.0  Potentiom. (G221) Current Value	  33.0  Potentiom. (G221) Current Value
  33.0  Potentiom. (G221) Specified Value	  33.0  Potentiom. (G221) Specified Value
  33.0  Min. Position (G221) (Lower Stop/Close)	  33.0  Min. Position (G221) (Lower Stop/Close)
  223.0  Max. Position (G221) (Upper Stop/Open)	  223.0  Max. Position (G221) (Upper Stop/Open)
	
18:06:17 Group 014: Center Flap Control Motor (V70) / Potentiometer (G112)	18:11:30 Group 014: Center Flap Control Motor (V70) / Potentiometer (G112)
  220.0  Potentiom. (G112) Current Value	  220.0  Potentiom. (G112) Current Value
  220.0  Potentiom. (G112) Specified Value	  220.0  Potentiom. (G112) Specified Value
  231.0  Min. Position (G112) (Lower Stop/Close)	  231.0  Min. Position (G112) (Lower Stop/Close)
  26.0  Max. Position (G112) (Upper Stop/Open)	  26.0  Max. Position (G112) (Upper Stop/Open)
	
18:06:17 Group 015: Defroster Flap Control Motor (V107) / Potentiometer (G135)	18:11:30 Group 015: Defroster Flap Control Motor (V107) / Potentiometer (G135)
  33.0  Potentiom. (G135) Current Value	  33.0  Potentiom. (G135) Current Value
  33.0  Potentiom. (G135) Specified Value	  33.0  Potentiom. (G135) Specified Value
  223.0  Min. Position (G135) (Lower Stop/Close)	  223.0  Min. Position (G135) (Lower Stop/Close)
  33.0  Max. Position (G135) (Upper Stop/Open)	  33.0  Max. Position (G135) (Upper Stop/Open)
	
18:06:50 Group 016: Air Flow Flap Control Motor (V71) / Potentiometer (G113)	18:11:37 Group 016: Air Flow Flap Control Motor (V71) / Potentiometer (G113)
  115.0  Potentiom. (G113) Current Value	  25.0  Potentiom. (G113) Current Value
  115.0  Potentiom. (G113) Specified Value	  25.0  Potentiom. (G113) Specified Value
  231.0  Min. Position (G113) (Lower Stop/Close)	  231.0  Min. Position (G113) (Lower Stop/Close)
  25.0  Max. Position (G113) (Upper Stop/Open)	  25.0  Max. Position (G113) (Upper Stop/Open)
	
18:06:50 Group 017	18:11:37 Group 017
  3.0  Vehicle Derivate  	  3.0  Vehicle Derivate  
  0.0  Convertible Top Status	  0.0  Convertible Top Status
       	       
18:06:58 Group 019	18:11:43 Group 019
  1.0  (no units) 	  1.0  (no units) 
  0.0  (no units) 	  3.0  (no units) 
  N/A   	  N/A   
  N/A   	  N/A   

 

The second stage is not pressurising, it should go up to just under 14 bar dropping to 10 bar when the fans cut in, if you had a guage set you would see the low side drop pressure at the same time. Those are guage pressures and I think VCDS measures absolute pressure so with the current heat 6 bar might even be a low charge, I dont have my charts to look at.

 

I would say that the modulating valve is not working and needs replacing, you will lose the system charge by doing the job and should ideally get the garage who will recharge it to recover the refrigerant before you work on it creating your own personal hole in the ozone layer, that way they can charge you to give you back your own gas

Is the modulating valve the n280 that's on the back of the compressor? Or should I be looking elsewhere?

 

I've got a friendly garage who can vacuum it down if they know they're doing the refill later.

Yes, thats the one, make sure that you bench test the new one with a 12v supply, also test the old one and compare them, you dont want to waste money on a recharge for a new valve that doesn't work, been there got the T shirt etc.

 

Also check that the shear plates have not broken on the pulley drive hub and also that the central nut is intact and turns when the engine is running and the aircon on max cooling, do that before degassing and changing the valve because it gives identical symptoms, I have had 2 hubs strip their splines out recently without the shear plate failing, both are probably due to the cheapo Chinese pump that I used but could happen if the nut comes loose like they used to on MK1's.

Edited 11 August, 20205 yr by J.R.

This is what you will need if its a problem with the hub or shear plate, - check compressor is not seized first.

 

https://www.ebay.co.uk/itm/COMPONENTS-OF-THE-COMPRESSOR-AIR-CONDITIONING-COMPRESSOR-THERMOTEC-KTT020055/293204553912?hash=item44445a70b8:g:csQAAOSwHBZdZqTW

 

Very hard to find especially at that price.

Thank you very much for your replies.

 

i will go on a hunt for that valve now.

 

As far as I can tell, the sheer plate is ok. The bolt is rock solid, and the whole of the sheer plate spins smoothly with the engine running. The fact that some pressure is built would suggest to me that it is ok, and driving the internals of the compressor.

 

 

 

 

I could not see from the scan that any pressure was being built, maybe I didn't look hard enough, remember that the pressure rises considerably with temperature.

 

When my hubs stripped the shear plate and everything rotated but the central spindle & nut didn't, it was almost impossible to see with the engine running although I have sight problems, the only way I could be sure was to slip a shallow socket & ratchet on the nut (very tight access) to find that it turned freely instead of being locked by the belt & pulley.

 

I think that problem was specific to me and the machining of the cheap pump that I bought though.

If you look at the compressor readings, there is no compressor current being utilised....so I suspect you have a ceased or jammed compressor.

The readout shows 820ma current which is the design PWM current when the compressor is supposed to be working at 100%with the modulating valve fully open.

 

None of them are actual measurements and they should all be taken with a pinch of salt.

There are 2 sets of reading side by side above, though looking at it on my phone it has mashed them together a bit.

 

If I set it to desktop view it looks Ok.

 

Watching with VCDS there is an immediate jump in pressure when the AC switch is turn on, and that gets up to about 8 bar before dropping off back down to about 6 bar.

 

As I said, I will try and source and N280 and see how that goes.

 

 

 

 

 

 

That sounds more like a low refrigerant charge, the low & high side (where the sensor is) are equal when the aircon is not running, at current ambient temperatures it should be 100-110psi, if VCDS gives absolute pressure then 6 bar is probably OK  but doing what it does is an indication of low charge, it raises the high side initially but then is starved on the suction side.

 

I would ask the garage to do a recharge & if it doesn't cool then get them to vacuum back the refrigerant allowing you to replace the valve which does actually sound like its working.

 

The radiator fans should cut in when the pressure peaks and then it should drop off but I dont think yours is going high enough.

His table above shows 4 bar G65 pressure with engine not running, that does indeed seem low for the ambient temperature recorded of 34°C. Slightly puzzled by why the engine coolant temperature is showing as 11° higher still. Was the front of the car facing South?

 

 

@J.R. We should both compare VCDS and high side gauge readings to put to bed this question about whether VCDS talks absolute pressure or gauge; I'm almost sure it's the latter, due to empty systems showing a 0.0 bar pressure, not 1.0 bar. 

 

I can definitively say that VCDS talks absolute boll***s a lot of the time

 

I will check next time, I have checked before but I have no short term memory 🥴

 

VCDS is great for on the fly readings and to see all the other parameters like you did above, once I am working physically on the system its the guage set that I use.

 

I will take this opportunity to ask you a question because I know that you like me are doing a self learning A/C apprenticeship.

 

I keep reading that I should vacuum down a system for 30 minutes, 40 minutes or even one hour to remove all moisture contamination, I can understand the leaving it for an hour to test for leaks but my pump pulls a -1 bar vacuum within a coupleof minutes and I really dont understand what is the point of leaving it labouring for another 45 minutes, any moisture will have turned to vapour and have been evacuated with the air or gas within the system, its not like leaving a fan blowing or a dehumidifier running, will it really remove any more moisture?

Edited 12 August, 20205 yr by J.R.

Just from an outsider's perspective, I'd be inclined to vac and relax the system several times over say half an hour then flush and vac before refilling.

 

Overkill?

 

Perhaps the lengthy period you read is considering large amounts of contaminants that may take a while to fully vaporise and be evacuated.

@J.R. I suspect the lengthy dwell time at vacuum is to give the dessicant in the drier time and opportunity to give up any/all contained water.  

 

That's my best guess anyway.

Edited 13 August, 20205 yr by Wino

MicMac.

 

I dont think that's a good idea if by relax, you mean let it fill with air again, the air is very humid at present. Maybe you meant hold the vacuum & then switch the pump back on several times.

 

My knowledge of the gas laws & from dive training et etc is that as soon as pressure is reduced the boiling pint of all liquids reduces immediately & they gas off if they reach their threshold, when you open a bottle of carbonated sugary coloured water the bubbles are produced straight away, they dont continue for 45 minutes, or maybe they do, I havn't touched the muck for decades.

 

Some googling needed methinks.

The first hit seems to be on the fence and cover all bases:

 

A vacuum of about 500 microns or 29.92 hg gauge pressure is needed for removing any moisture that may have entered the system along with the non-condensable gases while it was open. The automotive A/C system must hold the vacuum of 29.92 in Hg for at least 1 minute.

 

With a vacuum pump connected to both, low and high air conditioning system sides pull a deep vacuum for at least 5-45 minutes.

 

Some interesting knowledge though.

 

https://autoacrepair1.com/how-long-to-evacuate-the-auto-a-c-system/

Edited 13 August, 20205 yr by J.R.

This one I need to read through several times to understand better but the gist that I get from it is that you can pull a vacuum yet still have moisture present which will cause the vacuum to diminish slightly, several subsequent evacuations may be needed.

 

I think I need a proper vacuum guage, my pump does not have one and the one on the manifold set only has a tiny portion of its range for vacuum.

 

https://www.trutechtools.com/Vacuum-Training_c_1100.html

Sorry for the thread hijack and to keep posting links, this one makes the most sense to me and is written in a very readable and understandable format:

 

https://www.contractingbusiness.com/refrigeration/article/20865898/refrigerant-evacuation-dont-be-a-clockwatcher

 

Clearly longer is better and I need to get a proper micron guage, when my guage shows a vacuum there is more to be pulled assuming that my pump is up to the task and that takes time, a micron guage would show me when to stop and also indicate any moisture remaining in the system.

 

I am beginning to realise why it is the enemy of cooling and that the compressor and pump oils become contaminated with it.

@J.R.I'm fine with the Thread hijack, this is all useful information for anyone trying to look at their aircon.

 

@Wino Yes, the car had been in the sun all day, so it's no surprise that the coolant temp was above ambient.

 

For now, the car has had a regas, and we are now at 6.6bar steady state, rising to 10, then dropping to 7.6 bar when the engine is running and AC turned on. When driving you now get small intermittent blasts of cool.

 

I'm ordering a replacement solenoid valve, which should be here next week, which I'll get fitted and see how much that improves things again.

Do the radiator fans come on?

See what compressor  shutoff code - if any - appears when it goes from working to not.

Edited 13 August, 20205 yr by Wino

I would say from the temperatures and pressures they are coming on and the system is cooling and pumping, I would suspect the flaps but there are no fault codes or compressor shut off codes.

 

A mystery that I would like to hear the cause of when it becomes known.

 

I recieved a thermometer today from Ali-Express that will go into the vent ducts, I did back to back tests on the Yeti and Octavia with it, its only a small analogue dial so not that accurate.

 

The ambient temperature was 30°c and idling at a standstill the Yeti took the duct temperature down to 5°c, the Octavia to 10°c yet last week the Octavia felt like it was cooling much more than the Yeti, I had however just regassed it and was forced to use a nitrile O ring on one of the pump connections so some of the charge may have been lost.

 

Later on I will compare the engine not running static pressures of both using VCDS.

 

Both cars would drop the temp additionally between 1 & 2° when the recirculating function was used, not as much as expected with such a high ambient temperature.

I will also check with my guage set to see how high the high side goes before the cooling fans drop the pressure.

 

I dont know if either of my vehicles has too much or too little charge but maybe the measurements will give an indication.

No cutoff code, that stays at 0. And fans sounded like they were running, but I didn't check under the bonnet to see which ones were active.

 

I was suspecting the flaps before, but now I've felt some cool from it, I think that is less likely.

Recent experience with the glovebox out shows that having A/C on closes the recirculation flap (no external air flow) on the blower regardless of manual recirc setting.

 

I imagine that's to cool the interior more effectively and upon reaching a low enough cabin temperature it would then open partially/fully allowing fresh air in.

Edited 13 August, 20205 yr by MicMac