aircon expert needed

[fred_raven]

Ok so have a problem with my w211 aircon! hadnt been regassed for a while and was getting to the point of only just working, tried a diy regas kit but didnt really work ! Whilst doing this and with help from guy who sold kit to me discoveredthe following , pressure at low point too high ( 60 - 70 psi) and not reducing when aircon is turned on , or off for that matter! There is no clicking sound when aircon is switched on so suggested that a check on voltage at compressor , starts at 1.3v even when off , when switched on goes up to 13v but soon drops again to 1.3v , after 20 secs or so goes up to 13v again for cpl secs then back down to 1.3v ! Had read that the gas should be replaced and this probably hasnt been done so went to kwikfit , who did a full drain test and refil and after a quick check when starting the car decided it wasnt fixed so ... NO COST !, techie did check and said compressor is turning ! on drive home car was getting much cooler tho ! but have since discovered that when car is only ticking over car lets out warm air !! so my guess is there is a problem with one of the sensors but ! Any ideas gratefully recieved!

 

[BlackC55]

I would be looking at a possible fault with the heater valve. Very common fault on the 211's.

It needs to be plugged in firstly to check the AC values and fault codes.

 

[fred_raven]

hi thanks for the reply , forgot to add that did pop in to my friendly indie yesterday who put it on star and did get a cpl of errors , these were cleared and he thought either a gas problem , now erradicated , or possibly the valve ! When you say heater valve , which one are you referring to ? the only one i can see on the russian site is the duo valve ! I know these are problematic , had to replace one on my w210 !

 

[fred_raven]

compresor connections

Having done a lot of digging , i am assuming that there should be 2 electrical connections too the compressor ! one for power and one for coil sensor ! if that assumption is correct then this could be my problem as when checking the other day i did find it odd that although there were 2 terminals there was only one wire connected ! so maybe the other has broken off and is loose inside the sleeving/ cover somewhere! anyone know for sure before i go searching for something in vain ?

 

[BlackC55]

It is only supposed to have one connector with one wire.

The heater valve is like a duo valve but made of plastic. They often fail.

 

[fred_raven]

ok , checked with local mb parts and valve only £28 so not too bad , I read that it can be a bugger to change but lot easier if the whole wiper assy is removed first! What I am still bit unsure of tho, still , is would a faulty valve stop the click / clonk u should get when turning the a/c on?

 

[BlackC55]

Do the valve first. They are such a common problem that it will probably need doing at some point. Was the AC values checked on the star.

 

[Van Vitesse]

The power to the clutch on the compressor is dropping in and out due to a fault. It is probably cause by either your HP or LP switch. If Kwik fit hadn't recovered and refilled the system, I would have said it was overcharged when you initially used the DIY gas.

Assuming that Kwik Fit have got it right, which is not very often, you either have a blockage, probably at the Expansion Valve, OR it is just Short Of Gas and leaking out almost as quick as you are charging into the system.

My best guess is compressor tripping on LP (Low Pressure) due to a leak on the system.
Find the leak, fix it, fit new dryer/receiver, vac and recharge.

 

[fred_raven]

I obviously tried the diy refill because it wasnt working properly , so dont think me overfilling is a possibility ! When kwik fit did the refill , it was connected to a machine , degassed, drained of oil , pressure tested, evacuated , regassed and then reoiled , no leaks shown ! and when i tried the diy job i checked LP pressure after about a week and still around 60psi ! But , not wishing to contradict Olly , but my feeling is that one of the valves is stopping the continuous 12v connecting to the compressor ! guess i could check the i/p and o/p voltage of each valve , or just connect 12v to the compressor briefly to see if that fires it up !

 

[Van Vitesse]

Hi Fred,

What Kwik Fit told you they did and what they actually did are very differant, but I wont bore you wth that right now, we will get into that another day if you want to.

It is worth disconnecting anmd checking the state of the HP & LP switches. They will be either Normally Closed (Continuous Circuit) or Normally Open (Open Circuit).

Check with the Engine Off and the AC powered off. If you can let me know the state of the Pressure switches we can decide where to look after that.

LP switch will be on the suction line and the HP switch will be in the discharge or Liquid line. There will possible be two or three HP switches on the discharge or liquid line. Just check them all and come back to me.

 

[fred_raven]

ok will do , just had quick look on russian parts site and only appears to be one temp/pressure sensor , on the hp side! but will check reality when i can get my hands dirty! btw , I was watching the kwik fit machine do its stuff more than their tech , so i know it did a full cycle !!

 

[Van Vitesse]

LOL at the Kwik Fit bit. Real refrigeration engineers do not use 'Those Machines' as we understand what is going on in the system. The rig you are talking about is for the Layman but completly useless if you do not understand what the fault is in the first place.

IF and ONLY IF, he has put oil in, (Which I doubt) then he may had lagged up the system with oil. There is NO WAY he took oil out unlsess he split into the system and blew it out with OFN.

I HATE thoses machines and we get so many people in here whom have been to 'Radip Fit' centres and had the AC system totally screwed or contaminated.

Note to everyone. Find your self a Competant refrigeration engineer for your AC servicing. It is a complicated system and your average Tyre Basher or Exhaust Fitter will not have the skills to understand the dynamics what is happening in your system or the control systems behind them.

NEVER tolerate have your system 'Topped Up' .

If it is Short of Gas, have the leak found and repaired. Its that simple, and its a legal requirement.

It does NOT Consume Gas, It does NOT Burn Gas, it does NOT leak or vent gas.

If they tell you it does, then they are mugging you and just setting themselves up for work in the future and more of your hard earned £££'s

(Off SoapBox)

 

[fred_raven]

ok , update time !! Still getting low voltage at the compressor with the plug disconnected , but managed to get a reading with it connected to the compressorand with a/c off around 6 v with a/c on 10.5 v !! tried to measure the temp / pressure switch but so tight of space made it just about impossible! Did diconnect the socket tho and the main fan immediately cut in so seems this is working ok ! So where from here? Still possible its the heater valve , but i cant understand how if this was faulty it would stop the clonk you are supposed to get when switching on the a/c , or the change of engine revs ! Oh and the car has done quite a few miles ( just over 250,200 )and am reluctant to spend more on it than I have to as it is probably going to be replaced soon!

 

[Van Vitesse]

Well this might be simpler than originally thought. Can you run a feed to the clutch (compressor) to see if it engages.

Although the voltage is low, which could be your meter, it sounds as if the AC system is 'Calling for Cooling'. I would expect battery voltage at the clutch wiring connector but without the specifics of your vehicle and/or compressor clutch, it is hard to tell.

Basically, I'd like you to run a power feed directly to the compressor. Thus will isolate the control circuit and we can see if the clutch actually works.

Most clutches have a single cable for +12v supply. The body of the compressor is the -12v connectoion or Ground if you like.

Some clutches have a + & - 12v Feed.

You will have to start the engine. Work safely. Make sure your temp supply doesn't get snagged in any pulleys or belts.

1. If clutch engages and compressor runs then we have a control fault on the vehicle still.
2. If clutch does not engage and you are sure we have correct power there (like it already seems you have) then you have a faulty clutch.

Can you try this and report back to here your findings. Should be quite easy. You will only need a short piece of cable.

NOTE!! Again be carefully if your temp cable isn't fused and you are running straight from the battery. Any mishaps could cause meltdown or worse but it is a fairly safe procedure if your work methodically.

Good luck.

 

[fred_raven]

No time to do any checking tonite.... but a little further info .. when engine runs at full driving speed then its cold ( 80 mls round m25 and i was almost an ice block ) soon as its in traffic then it seems as the car is not only warming but getting damper !! bit like it does when left in the heat for an hour and restated , feels clammy! dont know if this helps !

 

[fred_raven]

Ok then done some more delving !

Voltage going to compressor is

with centre a/c swith off ---- 0v
with centre on , a/c sw off---6.3v
with centre on , a/c sw on 10.4 - 11. 5v

no difference if i connect 12v ( act 13.2V)

generally a/c pipes cool or warm , but if i remove the temp/ pressure switch connector , firstly the fan kicks in , so presumably this part of it is working , but quite quickly the a/c pipes get cold again ! But does seem to be a bit intermittent! ie wont always stay cold ! but then i didnt want to leave connector off too long as the fan is then running at full speed !

I am guessing from this that it may be either too high pressure , or the sensor faulty ! If I change the sensor does that mean letting all the gas out and refilling , or is the element replaceable without a gas down !

 

[Van Vitesse]

Some good diagnostics info there. The pressure switch your are disconnecting is probably the 'HP control Switch', not HP Safety Switch. It must be 'normally closed' and then opens when the discharge pressure exceeds it's set point. This will start the condenser fan which will remove heat and therefore pressure from the system when the vehicle has no 'Free Air Movement'. As the pressure drops the switch would then close again turning off the fan.

It is fair to assume that whilst your are driving, the condenser fan would not normally run as there is plenty of 'free air flow' across the condenser. This sounds like the situation when you are driving along. (M25 scenario).

In slow moving traffic or stationary, the condenser fan will need to take the place of the free air movement.

If the fan does not start, the discharge pressure will increase and then it will activate another HP switch called 'HP Safety'. This will be set a little higher in value than the HP control switch.

This will turn off the compressor and send a signal to the ECU which will be stored as a fault code.

In any vehicle, especially older systems, when the AC stops after a period of running, any ice will melt off the evaporator (heat exchanger in dash) and drain as condensation. Often, especially as the evaporator fan will still be running, you will notice a dank musty smell. The cabin may also heat up just before or at this point due to un-condensed gasses entering the evaporator and actually warming it up instead of it's proper function of expanding and cooling.

Do you know anybody that can read any stored fault codes. An independent with a star pc perhaps?

I am pretty sure that the HP control switch has failed. Some switches screw into a schreader valve union which allows replacement without the need of refrigerant recovery. Your AC/Fridge engineer will be able to ID properly it.

I hope all this makes sense. I tend to waffle a bit but hopefully you are able to follow.

I think A fault code read was recommended at the beginning of this thread so credit there to the other member!

Unusual fault if it is HP control switch. Their pretty bomb proof but keep us posted.

 

[foru2justnv]

Hi
Van Vitesse
can I pick your brains as you seem to be quite clued up on this topic, I have a w210 E320 CDI, my compressor isnt engaging and neither the fans kicking in, got the air con pressure checked and they said it has 20 psi in it and needs topping up, I was actually going to get it done until i read this post, would it be fair to say with only 20psi and no compressor or fans kicking in that it was just low on freon? no point paying to recharge when it might just leak out or another problem in first place,
any help will be much appreciated

 

[Van Vitesse]

Hi
Van Vitesse
can I pick your brains as you seem to be quite clued up on this topic, I have a w210 E320 CDI, my compressor isnt engaging and neither the fans kicking in, got the air con pressure checked and they said it has 20 psi in it and needs topping up, I was actually going to get it done until i read this post, would it be fair to say with only 20psi and no compressor or fans kicking in that it was just low on freon? no point paying to recharge when it might just leak out or another problem in first place,
any help will be much appreciated

Greetings! If your system contains 20psi of static (Not Operating) pressure then the system will be held off on an LP (Low Pressure) Fault.
In basic terms it is 'Short Of Gas' or 'SOG'.

We classify SOG systems in two different ways.

1. Catastrophic Leak - Little or No Gas (Static Charge is 10 PSI or less)
2. Low System charge - System operates but provides poor cooling (Static Charge is usually higher than 40psi)

1a. The catastrophic leak is easiest to diagnose and a quick pressure test with Nitrogen (OFN2) will easily find the integrity problem. From here, the task is to identify the correct leaking components then price up the job to include the replacement parts and also to fit a new drier or sometimes a receiver/drier. A further pressure test will prove system integrity before re-commissioning and the customer goes away happy and cool. We can warranty the system knowing it will not be leaking and he will not be back in a few days or weeks wanting his money back because all his gas has leaked out. (If only I had a pound from every customer that came in with that story from other techs!)

2a. The system that has a lowish charge is a little trickier to diagnose. Again it’s not rocket science, but the vehicle has a leak somewhere. FACT.

Anybody just putting gas back into this type of system is just having a laugh with you. They either have been trained incorrectly, do not understand what they are doing or indeed do know what they are doing!!
Either way, you don't really want this kind of AC tech round you.

Have you system pressure tested by a competent engineer. Your tech should be asking you questions about the vehicle when he is performing his basic checks.

Things like, How long have you had the car? Any mechanical work been done recently? Any history of AC faults? Any bodywork damage or repairs? Have you had it topped up before? The answers to these question will help your tech build a picture to possible problems.

The older the car gets, the shaft seal can ware on the compressor. It is widely acknowledged that Vehicle AC system will leak 15% per year.

I DO NOT prescribe to this theory at all. It is just a smoke screen to charge a load of gas in, take you money knowing you'll get through the summer and be back again next spring.

Think about it...Would you tolerate Water or Oil or Fuel leaking out of your car? Certainly not.

I have worked on thousands of vehicles of all ages and makes and can honestly say that they do not NATURALLY leak refrigerant! Period.

Would you tolerate having you fridge indoors topped up yearly? No

Your AC system is no different. It a totally sealed for life system.

It is ILLEGAL (UK & EUROPE) to knowingly vent refrigerant or put refrigerant into a system that leaks. It ios a controlled substance.

Think about it, Car manufactures just wouldn't build something that leaks by design.

Anyhow, back to your problem. I’d guess you have a small leak somewhere on the system. Possibly shaft seal or a core in the condenser. Remember the condenser sits in front of your radiator. The first thing to get hit by the stone is now your condenser, not the rad.

Also due to their construction (mostly aluminium), they also go through an erosion process if not maintained properly with any materials around it like the vehicle chassis or even the condenser mounting brackets.

This causes the condenser to become porous and cause tiny amounts of refrigerant to leak. Hoses can chaff and leak but these are usually catastrophic leaks, not small ones like you seem to have.

Small leaks can take a long time to cause a problem. Sometimes over a year.

If you get the right tech around you, he will resolve any control and operational problems you have. He will also find and repair the leak properly and permanently.

But beware, some of the parts are costly which is partly why we have a culture or 'Suicide Bombers' as we call them here. Bomb charge the gas, take clients money and run knowing it will die at some point in the future.

One other thing be very wary of tech that put dye into a system. Another one of my pet hates. I can't stand the stuff. Its lazy and will only show up a leak that you can physically see! Also we go back to the 'suicide bomber' trait. The tech obviously knows it is leaking in the first place.

Insist they find the leak and accept no excuses. Excuses indicate that the tech is either inadequately experiance, incorrectly trained or immoral.

As I said it's not rocket science and ALL leaks can be found and fixed relativly easily with the correct tools and knowhow. Sadley I get somewhat disillusioned with the stories that get told in our office by unhappy customers.

 

[fred_raven]

ok , so the story continues !!

The aircon is working fine , when the car is continuously moving , but when stuck in traffic it soon blows warm ( very warm ) air ! initially thought that disconnecting the plug to the temperature/ pressure switch , which does cause the fan to start , also kicked in the aircon but that is not repeatable ! have now removed plug and left running for 5 min and still warm air ! Indeed if you feel the high pressure pipe at item 60 on the attached diag , http://img.partscatalog.ru/MB/E/E475286414ECAA1AD40566BAF833C8BD.gif , this is warm too. So it seems that when not moving at some speed the compressor is not working properly , where as at speed it is ! Dont understand what could cause this, any suggestions gratefully received ! thanks