Evaporator Anti-Icing

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deuchebleu
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Evaporator Anti-Icing

Post by deuchebleu » 08 Jul 2013, 22:38

Just replaced condenser on Xsara Picasso 1.6hHdi and regassed and all now cold but I have a slight concern regarding the operation.
Basically, when in slow speed traffic or stationary the high speed fan comes on for about 20 seconds every minute or so, the compressor declutches, the fan goes back to low speed, compressor engages and the cycle repeats. It's a two speed fan and the low speed is on at all other times. Now I've had this car from new and I don't recall it operating like this then, just the low speed all the time the aircon was on.
Anyway I stuck the Lexia on and had a look at it yesterday. Ambient temp was 24 deg C, aircon pressure 9 bar before starting engine going up to a max of 17-19 bar during operation. On Lexia the evaporator temperature heads downwards fairly rapidly to 0 - 0.4 deg C, Anti-Icing is activated, Fan on high speed, compressor declutched until evaporator temperature rises to 4 deg C, then fan back to low speed and compressor engaged and so on. I know the ideal is to maintain the evaporator at just above 0 deg C and it is doing this I'm just a bit concerned about the longevity of the fan relay and clutch given the rapidity of switching. No complaints otherwise, it's bl**dy freezing. My one thought is maybe it has too much gas in it although it was a reputable place that regassed it.
Any comments from aircon specialists appreciated.

John
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Re: Evaporator Anti-Icing

Post by fastandfurryous » 10 Jul 2013, 10:11

That does sound to me like the system is slightly over-full. It would be interesting to know what is pushing the system into "oshit" mode, as normally an evaporator anti-icing does not throw the fans into full speed, it only de-clutches the compressor. IIRC there's only a few things that cause the fans to run full speed. The most obvious is the HP part of the HP/LP switch, and I think also the coolant temperature sensor can do it too. (this is making the assumption that your A/C works the same way as 90's non-multiplexed cars). Given the rapidity of switching in and out, I'd suggest it is a system over-pressure that is causing "oshit" mode, which clears very quickly with the compressor de-clutched and the fans on full belt.
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Re: Evaporator Anti-Icing

Post by deuchebleu » 10 Jul 2013, 12:52

Thanks for the reply. I think it must work differently the 'oshit' mode is definitely anti-icing. There is a parameter, monitored in Lexia, which is called, appropriately enough, 'Evaporator Anti-Icing' and this changes state to 'Activated' as the evap temp reaches 0 deg C, then the fans go to High speed and then the compressor declutches. The system pressure doesn't change during this phase and the coolant temp is consistent too. I think it may indeed be overcharged and maybe never got the temp down to 0 deg C before, even when it was new. Given the normal yearly loss of gas it will probably be OK next summer. Interestingly enough I was standing outside talking to a neighbour yesterday and a Volvo V40 pulled up and sat there with the engine running while waiting to pick someone up and it was doing exactly the same thing, fan going to high followed by click of clutch disengaging and repeating at about 1-2 minute intervals.

John
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Re: Evaporator Anti-Icing

Post by Hell Razor5543 » 10 Jul 2013, 22:30

It might be worth posting up the last eight digits of your VIN number. When I had my previous Xantia re-gassed, they had to check which of 2 makes of compressor was fitted, so they could then tell their system. I wonder if there was a capacity issue? Maybe you could have the same issue?
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Re: Evaporator Anti-Icing

Post by fastandfurryous » 11 Jul 2013, 13:39

If it only occurs when you're stationary, I wouldn't worry about it. It's entirely possible that it should have been doing this previously, and was ever-so-slightly under-charged.

Just out of interest, Does it cycle in more with the interior fan on a slow setting, and somewhat less with the interior fan on full wallop?
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Re: Evaporator Anti-Icing

Post by deuchebleu » 11 Jul 2013, 22:16

The compressor is a Sanden model. I'm not sure of the model number or if different makes were fitted. However I found a table of capacities for the Xsara Picasso which ranged from 625g to 775g for the various models, with mine, the 1.6HDi DV6 engine being the lowest at 625g. So it is entirely possible it has been overcharged.
I think it only occurs when I am stationary as that is when it is obvious but it is difficult to tell when moving because of the general increase in background noise.
I think, if anything, it cycles more with the interior fan on a higher setting which is maybe the opposite of what you would expect but again it's difficult to be certain. When I say cycles more I think it leaves the high speed fan on for longer which is probably because it takes longer for the evaporator temp to rise by the 4 degrees hysteresis it seems to need. I do remember in previous years measuring the centre vent temperature and on fan speed 1 it was always a few degrees colder than on fan speed 2.
Thanks to all for the suggestions. Yes, I'm just going to live with it as it works fine otherwise and enjoy it while it lasts. I was initially just a bit concerned that it had never behaved like this before.

John
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Re: Evaporator Anti-Icing

Post by fastandfurryous » 12 Jul 2013, 09:39

deuchebleu wrote:Yes, I'm just going to live with it as it works fine otherwise and enjoy it while it lasts. I was initially just a bit concerned that it had never behaved like this before.

John


Of all the components I've ever seen fail, the compressor clutch isn't one of them. I suspect you could cycle the clutch a few hundred thousand times before it even thinks about failing.
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Re: Evaporator Anti-Icing

Post by Daniel.TM » 27 Jun 2016, 09:48

Hey John,

Your problem seems very familiar to what i had, with the compressor engaging for a couple of seconds and then cutting out. seemed to be at random.
the evap temperature safety feature was preventing it from working continuously, as Lexia Evap temp measurement gave similar figures, with the temp falling to minus after a second or two of compressor working.
I took the sensor out , in your case it should be on the right side of the console just beneath the panel under the steering wheel. might be with a connector but usually it is spliced directly to the cable loom, the wires are colored grey.
Take it out, most probably it would read an absurd resistance figure in tens of millions ohms, therefore it is defect.
Have it replaced, costs around 20 euros at the dealer(takes a couple of days to arrive usually) and in the meantime you can add a 10KOhm resistor between the leads - it will keep the compressor working fine.

Best wishes.
Daniel.
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Re: Evaporator Anti-Icing

Post by Daniel.TM » 27 Jun 2016, 09:53

AH and if you want to test whether the fault is with compressor or the BSI - you can use the actuator function in Lexia -> BSI, to cycle the compressor clutch back and forth. if it clicks then it not the problem.
If it doesnt, try first suppling power to the compressor - is it still wont budge, check with a feeler gauge that between the compressor pulley and clutch there is no more than 0.8mm of clearance, you can adjust it by removing the shims at the base of the clutch.
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Re: Evaporator Anti-Icing

Post by xantia_v6 » 27 Jun 2016, 11:57

Note that this topic is 3 years old!
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Re: Evaporator Anti-Icing

Post by deuchebleu » 09 Jul 2016, 17:16

As the original poster I thought I would just post a follow up on this thread now that it has been resurrected.
The aircon system has been untouched since my original post and it is still behaving exactly the same and still very cold so it would appear that I have not lost much gas in the intervening period.
Thanks to Daniel for taking the trouble to post a belated reply.
I did have the evaporator temperature sensor out during an investigation prior to replacing the condenser and it tested out OK.

John
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