Aircon evaporator icing up ??
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  1. #1
    BVH Roger Wilkinson's Avatar
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    Default Aircon evaporator icing up ??

    Hello team,

    I've recently had the airconditioning in my XM fixed up. New compressor, TX valve, received-drier. It's nice and cold but I had a strange experience driving home from Melbourne the other day. The temperature was in the high 20s. Suddenly I noticed that almost no air was coming through the vents yet the fan was obviously spinning. After a few minutes thinking and messing with the knobs I decided that maybe the evaporator was iced up, so I switched off the compressor and waited. Sure enough, after a couple of minutes the air flow returned and after a few minutes the flow was back to normal. It stayed cold for several minutes, even though the compressor was switched off.

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    I cannot imagine that it could have been anything other than the evaporator being iced up. Is this common? Is there anything that can be done about it?

    Thanks,
    Roger

  2. #2
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    Quote Originally Posted by Roger Wilkinson
    Hello team,

    I've recently had the airconditioning in my XM fixed up. New compressor, TX valve, received-drier. It's nice and cold but I had a strange experience driving home from Melbourne the other day. The temperature was in the high 20s. Suddenly I noticed that almost no air was coming through the vents yet the fan was obviously spinning. After a few minutes thinking and messing with the knobs I decided that maybe the evaporator was iced up, so I switched off the compressor and waited. Sure enough, after a couple of minutes the air flow returned and after a few minutes the flow was back to normal. It stayed cold for several minutes, even though the compressor was switched off.

    I cannot imagine that it could have been anything other than the evaporator being iced up. Is this common? Is there anything that can be done about it?
    Shouldn't there be a temperature sensor on the evaporator which shuts off the air conditioning before the evaporator gets to freezing point ? I'm sure the Xantia air-con has one....(or any air-con for that matter, or this problem would be happening to everyone...)

    Maybe that sensor isn't working....(was any work done on the evaporator ? Could it have got dislodged ?)

    Regards,
    Simon
    1998 Xantia Mk2 V6 Auto Exclusive

  3. #3
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    Roger,

    Don't you remember having this problem with our XM on the way back from Citin? Just keep the fan going fairly fast and it doesn't ice. Had the same problem in the sweltering Hobart heat, fast fan - no problems, slow fan - iced up.

    Great car despite its little ways,

    Peter

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    Moderator Alan S's Avatar
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    I've always found that if the fresh air vent is left open on BXs that they will ice the evaporator almost within a couple of minutes. With them, they have to be set on recirculate particularly when they've been converted to R134a.
    I live in an unbelieveably high humidity area (75% + is common) so we possibly notice it more than people down south unless extreme conditions prevail down there.
    My idea is that ice forms on the sensor and immediately this happens, it will not sense much above or below 0 degrees as a result the compressor will just keep pumpin and getting the evaporator well below freezing point. Air containing moisture (humidity) then builds up on the fins and cuts off the air circulation with the result that the temperture rises.
    Xantias for some reason don't seem to have this problem but I've never gone to the trouble to find out why; if it works, leave it lie is my motto.
    I presume as XMs and BXs are of the same vintage, then they will possibly have the same type of system design, so if it is set on recirculate when operating the air/con, that should stop the problem.


    Alan S
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  5. #5
    BVH Roger Wilkinson's Avatar
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    Quote Originally Posted by Alan S
    I've always found that if the fresh air vent is left open on BXs that they will ice the evaporator almost within a couple of minutes. With them, they have to be set on recirculate particularly when they've been converted to R134a.

    My idea is that ice forms on the sensor and immediately this happens, it will not sense much above or below 0 degrees as a result the compressor will just keep pumpin

    I presume as XMs and BXs are of the same vintage, then they will possibly have the same type of system design, so if it is set on recirculate when operating the air/con, that should stop the problem.

    Alan S
    Thanks for that explanation Alan. I think you're saying that even if the temperature sensor on the evaporator is working it won't stop the compressor once it has iced up, and for whatever reason it won't stop the compressor before it has iced up either, so it must be set for a temperature below zero degrees.

    An XM is just an overblown BX so your recirculate suggestion probably holds true. Is the reason for using recirculated air that it has already been dried so won't leave moisture on the evaporator fins to ice them up? I must say I like my fresh air and almost never use the recirculate setting. I might just leave it on the outside air setting and if it happens again try about half and half outside and recirculate and see what that does.

    What is it about R134a that all makes this more likely?

    Roger

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    BVH Roger Wilkinson's Avatar
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    Quote Originally Posted by PeterJ
    Roger,

    Don't you remember having this problem with our XM on the way back from Citin? Just keep the fan going fairly fast and it doesn't ice. Had the same problem in the sweltering Hobart heat, fast fan - no problems, slow fan - iced up.

    Great car despite its little ways,

    Peter
    I'd forgotten all about that Peter. I've always just left the fan on auto and been happy with whatever speed it has dialled up for me. But I will try your suggestion.

    Roger

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    Moderator Alan S's Avatar
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    Ice in itself is an isulator so once the ice covers the sensor, it loses it's ability to sense the varying temps.
    As regards the R134a I haven't gone into the techicalities but suspect it's a different pressure at which it boils off and so may tend to lower actual coil temps..
    Sensors in BX evaporators are usually fixed between the fins on the cabin side of the evaporator; we recently fitted a variable thermister (as suggested by KenW in the common problems and fixes archive) on the outer side of the coil and found it gave much better temperature control.


    Alan S
    If it ain't broke, use a 12" shifter.....that usually does the trick!!

  8. #8
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    Roger
    You could also locate and clean the years of dust and crap off the cabin temp sensor. On mine it is in a holder and "vent" near the overhead light. I think on yours it may be in the dash. Vent holes are slotted and about the diameter of a 5c piece.

    Theory being that the sensor is so clogged up it is thinking the ambient temp is much higher than reality and flogging the aircon to death and not activating the balance flap between hot and cold air.

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    Craig K
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    Moderator Alan S's Avatar
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    Do they have a full on climate control on the XMs?


    Alan S
    If it ain't broke, use a 12" shifter.....that usually does the trick!!

  10. #10
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    Quote Originally Posted by Alan S
    Do they have a full on climate control on the XMs?


    Alan S
    Roger's is S1 and mine is S2, and the answer is yes. Although in the S1 I think it is a dial temp like in some Xantias.
    Craig K
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