Technical Air con and blower problem

[bob404]

Hi I wonder if anyone has any ideas on this, our 500 S has an issue when the air con is on, what happens is that the blower slows right down to almost nothing, as it slows you start to see a cold mist coming out of the vent.
The only way I have found to get the air blowing again is to turn off the aircon and wait, after a few minutes you start to feel the air blowing again - its almost like something is freezing up inside, now this only happens when you use the car after a couple of miles - so if on the motorway its really noticeable as its freezing up all the time, if you leave it parked (at the garage for them to test!) and switch it on then it happily works - I have had the refrigerant gas levels checked and the filters changed.

Any ideas/suggestions appreciated!

 

[chris3234]

Do you see any water dripping out under the car with the air con on?


Wonder if the drain line is blocked and water can't drain away from the evaporator

 

[bob404]

Do you see any water dripping out under the car with the air con on?


Wonder if the drain line is blocked and water can't drain away from the evaporator

Thanks, just had a look and checked the drain from outside and inside, its all clear and connected properly.

 

[John202020]

Electronic control or turn knob for fan speed?
If manual on max does it still do the same thing? Is it only when the ac is on or anytime?
The mist is it freezing or moist
Does the compressor click on and of whilst driving ?

 

[bob404]

Electronic control or turn knob for fan speed?
If manual on max does it still do the same thing? Is it only when the ac is on or anytime?
The mist is it freezing or moist
Does the compressor click on and of whilst driving ?

Thanks, its turn knob for fan speed,
I usually have it on 2 or 3, and then notice the air has virtually stopped coming out (ususally hear lots of clicking behind dash like when something is expanding or contracting due to heat/cold and usually if i turn ot up to 4 at that point we get little icy flakes come out as well as the mist) I will try it starting on 4 and see if it happens
Yes its only when ac is on
The mist is freezing,
Havent noticed a distinct click on and off from the compressor, will listen for this.

 

[AndyRKett]

The only way I have found to get the air blowing again is to turn off the aircon and wait, after a few minutes you start to feel the air blowing again - its almost like something is freezing up inside, now this only happens when you use the car after a couple of miles

if you leave it parked (at the garage for them to test!) and switch it on then it happily works

y if i turn ot up to 4 at that point we get little icy flakes come out as well as the mist

The mist is freezing,

I'd hazard a fairly well educated guess that the evaporator is freezing up.

Firstly do you have a pollen filter in the car or has this been removed. Removing the pollen filter does cause crap and detritus to get on the evaporator which creates a good surface for growing ice crystals, the filter also catches some of the moisture in the air which can freeze up the evaporator.

The next thing to check would be to get it on the computer and see what the pressure switch is registering. If the switch is faulty or stuck the system may not be cycling on and off like it should, and therefore running constantly causing icing of the evaporator. (this is a more likely cause)

The thing to remember here is if the flow of air is being blocked by the ice build up, then it is seriously stressing the wiring to the blower motor which can very quickly and easily burn out, this is a common cause of fire in cars where the pollen filter is not changed, causing a high air resistance and therefore over stressing the blower motor and over heating the wiring.

I think its highly likely the pressure switch has failed, but it will need an aircon specialist to replace as the gas needs to be taken out and put back in once the pressure switch is changed.

 

[John202020]

Remember there's a sensor in the evap area also so if it's faulty it may hold the system on all the time?
And you can really feel the load on the engine when driving when the ac clicks on, turning the ac off whilst accelerating is like turbo boost

 

[bob404]

I'd hazard a fairly well educated guess that the evaporator is freezing up.

Firstly do you have a pollen filter in the car or has this been removed. Removing the pollen filter does cause crap and detritus to get on the evaporator which creates a good surface for growing ice crystals, the filter also catches some of the moisture in the air which can freeze up the evaporator.

The next thing to check would be to get it on the computer and see what the pressure switch is registering. If the switch is faulty or stuck the system may not be cycling on and off like it should, and therefore running constantly causing icing of the evaporator. (this is a more likely cause)

The thing to remember here is if the flow of air is being blocked by the ice build up, then it is seriously stressing the wiring to the blower motor which can very quickly and easily burn out, this is a common cause of fire in cars where the pollen filter is not changed, causing a high air resistance and therefore over stressing the blower motor and over heating the wiring.

I think its highly likely the pressure switch has failed, but it will need an aircon specialist to replace as the gas needs to be taken out and put back in once the pressure switch is changed.

Thanks,
The pollen filter has recently been changed when I had the garage check the refrigerant (the old filter was apparently very dirty). Have called into the garage today so I could show them the fault - I mentioned the pressure switch, he wanted to discuss it and get back to me in a couple of days. So will see what he says then.

 

[bob404]

Remember there's a sensor in the evap area also so if it's faulty it may hold the system on all the time?
And you can really feel the load on the engine when driving when the ac clicks on, turning the ac off whilst accelerating is like turbo boost

I tried it on fan setting 4 and the same thing happened but it took longer for it to freeze up.
Oh and I tried turning off the AC but no turbo boost for me! In fact its hard to tell any difference when its on or off, but you can hear the ac click on or off.

 

[John202020]

If the system clicks on and off then generally it's working correctly. The pressure switch is only there to stop the system working if say there's very low refrigerant or the opposite far too much, then there's the evap temp sensor.

Excessive icing is generally a lack of air flow, most often blocked filters or a air flow blockage in general ?
I'd be tempted to pull the filter replace the cover and try even though it's new ?
Ideally you need to look inside to check theres not something inside?
The ac drain, was there evidence of water running out, can be really quite a lot

Contact a proper ac specialist rather than a garage?

 

[bob404]

If the system clicks on and off then generally it's working correctly. The pressure switch is only there to stop the system working if say there's very low refrigerant or the opposite far too much, then there's the evap temp sensor.

Excessive icing is generally a lack of air flow, most often blocked filters or a air flow blockage in general ?
I'd be tempted to pull the filter replace the cover and try even though it's new ?
Ideally you need to look inside to check theres not something inside?
The ac drain, was there evidence of water running out, can be really quite a lot

Contact a proper ac specialist rather than a garage?

I will check the filters next, thanks - what I dont understand is that the blowers are still blowing just virtually no wind is coming out its almost like something has closed inside,
yes i think i need a specialist too

 

[John202020]

Has the fault happened suddenly? Was there any work just before?
With the fan on ac off can you control the direction of air flow say top vents only or screen? And is the air flow as expected or as a year ago say?
If you then turn on the ac whilst stationary does the fan slow down as it gets colder or only the air flow rate? If it's not hot outside then the compressor should only run less than a minute before cutting out, if it's quite hot then it could easily run continuously whilst standing still.
Trying to work out if it's a control issue ( too much compressing )or air flow restriction (say a bit of broken off filter or general rubbish even though it shouldn't be)?
Whatever can you come back once you've hopefully found the fault.

 

[bob404]

Has the fault happened suddenly? Was there any work just before?
With the fan on ac off can you control the direction of air flow say top vents only or screen? And is the air flow as expected or as a year ago say?
If you then turn on the ac whilst stationary does the fan slow down as it gets colder or only the air flow rate? If it's not hot outside then the compressor should only run less than a minute before cutting out, if it's quite hot then it could easily run continuously whilst standing still.
Trying to work out if it's a control issue ( too much compressing )or air flow restriction (say a bit of broken off filter or general rubbish even though it shouldn't be)?
Whatever can you come back once you've hopefully found the fault.

Embarrasingly no, my wifes car and I happened to drive it for a long drive and then I discovered the air con wasn't right - to which I was told "I thought that was just the way it was".... only had it 18months
Air direction works fine with both ac on or off.
I haven't tried it stationary myself (the garage did) but I will try this to see what happens

I had a look at the pollen filter today - garage had done a top job, the cover was loose, one screw was under the mat and the other only half screwed on. Looking inside it looked clean enough apart from the leaf at the back which I removed - pic attached.

 

[John202020]

That looks really nice and clean
The filter is a bit of a pig it seems our car doesn't have ac but our elderly mazda has filter change takes 45 seconds, so the fault seems to have been present for quite some time I'd definitely contact a car ac specialist from now on.
Once it's fixed suggest you leave the ac always on especially in winter, trust me it's the best way to preserve the ac system and for those that say it gets too cold, turn up the heating!

 

[bob404]

So after I refitted the pollen filter cover properly.
I first ran it for 30 mins stationary (as I hadn't done this myself), and no freezing up, you can see a puddle under the car from the drain, I would also say the ac temp was slightly warmer than on a run.
I then took it for a drive and it took a lot longer before the ac started to freeze up, last time it was about 4.5miles, this time it was about 8 miles, so improving the air flow definitely helped it. Which got me thinking about an evaporator temperature sensor, but cant seem to find anything as to where it may be as I could check thats working too

While searching I came across this on a BMW Forum now I know its a bmw forum but interestingly a very similar issue - and they fixed it via firmware update!
I cant seem to find any AC Specialists locally that dont look like general garages so not surewhere to go next, dont really want to go to days fiat.....

 

[AndyRKett]

So after I refitted the pollen filter cover properly.
I first ran it for 30 mins stationary (as I hadn't done this myself), and no freezing up, you can see a puddle under the car from the drain, I would also say the ac temp was slightly warmer than on a run.
I then took it for a drive and it took a lot longer before the ac started to freeze up, last time it was about 4.5miles, this time it was about 8 miles, so improving the air flow definitely helped it. Which got me thinking about an evaporator temperature sensor, but cant seem to find anything as to where it may be as I could check thats working too

While searching I came across this on a BMW Forum now I know its a bmw forum but interestingly a very similar issue - and they fixed it via firmware update!
I cant seem to find any AC Specialists locally that dont look like general garages so not surewhere to go next, dont really want to go to days fiat.....

Being manual air con I do not think your car would have any sort of temperature sensor on the evaporator.

I also do not suspect there is any "firmware" to update on manual air con, The pressure sensor sends the signal to the ECU and from this the ECU decides to turn the aircon compressor clutch on and off. It's a pretty dumb system and works on a closed loop. The BMW may have had a much more complex system than fiat would use in their cars and therefore there may have been something to update the firmware on.

Thinking about this a little more, you may have a failing expansion valve This valve/block controls the rate at which the gas expands as it enters the evaporator. If the gas expands too quickly, then the evaporator will get too cold. Thinking about this, this is the most likely cause of your issues, its quite a common failure point on some other cars. The job of the valve is to regulate how much gas goes into the evaporator, based on the pressure of the gas coming out.

Explanation of how it works here -->https://www.howmechanismworks.com/2018/09/how-expansion-valves-works-in-air.html?m=1

really you still need to find an Aircon specialist who knows what they're doing to confirm this, there are loads of them about, a 30 second search of "automotive aircon specialist swansea" turned up this company --->https://red-dragon-airconditioning.com/mobile-ac-services/ I have no idea how good they are but it goes to show there are companies about.

 

[bob404]

So we have tested and ruled out the pressure sensor, it certainly seems related to air flow as when the ac was starting to freeze up the other day and I tried turning up the heater to see if that would help (without turning ac off) and strangely from the two air vents above the stereo I had cold air out of one and warm air out of the other so now I am thinking is this something to do with a "flap" inside not working properly so possibly an actuator? Will have to replicate this as I can't remember which side the hot was coming out.

 

[John202020]

Uh oh, the "blend door" issue is known about, and there's only a few places in the country that can fix it