Aircon not kicking in immediately

[KLee]

Ok will try the a/c control unit bit after I ascertain all ok with the other parts to check. DrNick how can I diagnose if I have a problem with the duovalve? The fans blows external air in and is working well, at all speeds on the dial. Trying to get to the cabin temperature sensor, shining up I can see the round hole with something thin and dusty coming down in the middle of it.

I have also been trying to think back if warmer air has bbeen blowing through the vents relative to outside air. Read somewhere that could be possible thus reducing the efficiency of the a/c and maybe in my case crippling it or the duovalve? Thhinking back, whilst in UK in 2002 during winter the heater did blow hotter air than normal sometimes at prolonged periods even when the dial was turned to the white areas but it doesnt seem to happen now - perhaps back then I just got the car so wasn't familiar with MB heaters requiring very small adjustments for heating.

Is there a accurate test I can perform to check heaters are operating as specified?

Btw where does the cabin air vents draw air from, where is the mouth?

 

[DrNick]

The duovalve is not likely to be your problem. This controls the hot water going into the heater. On mine it failed in a way that hot air always came out of the passenger vent, regardless of the heat setting. The valve itself is located in the engine bay, just in front of the brake servo on my E.
I proved the problem by swapping the wire on the duovalve and the problem moved to the drivers side, showing the valve was at fault, rather than the controller (thats to Dieselman again)

As far as I understand the system, the AC is always on if the red light is off, irrespective of the desired cabin temperature, so the cold air is heated if necessary through the heater. If this is true then internal temperature sensors are not the cause of your problem. The system you (and I) have is actually a climate control, just not digital, so it is correct that you get hot air out at first on a cold day as it tries to warm the cabin, as its trying to maintain a constant temperature. The compressor will run to keep the evaporator at a low temp rather than the interior of the car.

One for the experts: Does the system drop the compressor out if the battery is at a low voltage to remove excess loading? Low battery has caused many woes on this forum!

 

[KLee]

DrNick, thks so much for your descriptions. I understand better now the operations of our analogue 'climate control' with regards to using a/c and the heating unit. Its an important lesson for me that the compressor runs to keep the evaporator at a low temp (fedback from temperator sensor inside it right) rather than the interior cabin. Cabin cooling is achieved by absence of heat in the heating unit which is placed after the evaporator, right. Interestingly my MB Manual says for basic summer cooling mode to have the temp selector turned to white in the middle! I have been having mine at blue always here in the hot aussie summer, have I taxed the compressor too much?

Hmmm so you deduce the cabin temp sensor is most likely not the cause I was hoping for a cheap fix. Should I bother cleaning it? I was about to ask questions re dismantling having read the rear view mirror HOWTO - do I really just pull down at the RVM - so worried it'll break.

I've found my Diavia W202/W210 Auto Air Con Use and Maintenance Manual to read up on what Bazzle said. Firstly the final line in the Use of A/C Notes section says

"The button which activates internal air recycle is timed: It activates for 5 minutes. After this time, the button must be pressed again in order to restore air recycle."

Mine does behave like this thus operates as Diavia designed so my a/c control box must be mated/programmed by Diavia, however in my MB Owners Manual pg 27, it says:

"The system switches over automatically from recirculating air to outside air,
- after 30 mins at outside temps above 5deg Celc
- after 5 minutes at outside temps below about 5deg Celc
- after 5 minutes if economy mode is selected
At high outside temps the system switches over automatically to recirculating air. The recirculating air mode switches off after about 30 mins."

Hmm, ok thing is, I have never seen the outside temp displayed on my dashboard. My manual mentions it on pg 85, I do not know if I physically have one on the car - judging from other threads its possibly an option but if it isn't wired for feedback into the above decisions I don't see the need for one. Is the absence of one in the face of what I have mentioned above a cause for concern?

 

[KLee]

Guys, do I need an external temp sensor? n would it be able to be fedback into the a/c control unit?

I've Been thinking that perhaps my best bet is to start dismantling the dash centre to get at the a/c control unit n get its part number n get some secondhand quotes. Then whilst I have it out, get someone or some advise how to test it is working. What do you think about this?

When i went to get the car off the a/c mech, he had his assistant put back the panel where the leg vents are in the front passenger foot well. What related to a/c is down there?

 

[KLee]

Finally had a crack at getting to the a/c control unit. With the HOWTOs it was quite easy and fun dismantling the sunglass box, then push out radio, then off with the wood trim panel and pull out th fan a/c controls and whalaaa the elusive a/c control unit with rightly the daftest loking white stalks behind the air direction dial.

The part number was found on the top of the unit, mine read 210 830 0185? Is this correct and can someone please confirm cos although its there it seems printed on the case and just wondering whether it referred to the innards too (or just the housing)? There was a barcode sticker on the bottom with Edmontage PL printed on it. Ring any bells?

 

[Bazzle]

That part number is correct. one with 170 in front will work too but dials will be white.

I got one from USA Your one is $80 US Mine 170 is 125 US. Mine came to $200 ozzie delivered.

http://www.mbpartsonline.com/recycled.html

All MB parts are fairly priced ther too.

They do PayPal which makes transactions very easy.

Bazzle

 

[KLee]

Thanks bazzle, that is v cheap indeed - luckily for me this time it isnt the part that caused my troubles. (sigh of relieve - although the labour that did go into the investigations went into the hundreds) I believe my duovalve is most likely the next item to shop for (another for MB) - found anywhere to get these new and less $? (Would appreciate your list of part sources since we are both in oz)

 

[KLee]

So Bazzle did your new shiny AC control unit work and solve your problem? I want to replace my pollen filter which is located under the passenger dash, have got the existing one out and vac it but still smells bit musty and side vents air flow still muted compared to other cars. Got quoted A$85 from sydney stealerships - in UK these are something like GBP10!! No? You know where I can source this cheaper within oz, pls?

 

[DrNick]

Looking back though the thread, I can't see how your problem is related to the duovalve. The duovalve controls the flow of hot water to the heater matrix. If you have some control over the temperature coming out of the vents when you use the thumb wheels, then the duovalve is probably working OK. It has no bearing on air conditioning. Duovalves usually fail one side first, usually resulting in very hot air coming out of one side whatever the dial setting. They can go intermittent but they have no input to the AC system!

 

[Glenn Smith]

Sounds to me like its short of gas, the press. switch on the receiver drier senses if there is low press. due to gas loss, or high press. due to fan not working. in either case it turns off the compressor, in the first case to prevent compressor damage and the second to stop press. going too high. Get it vac'd out and recharge before looking any further, leaka are the biggest problem by far on aircon systems and out way all other faults put together, Is the heater fan working?

 

[KLee]

Thks for the extra input guys. the original AC problem of not coming on itself is fixed - sorry my mistake for not updating this thread accurately - I did in another thread. It was fixed after extensive manual wiring diagnosis resulting in 1 faulty relay and 1 fuse (long story). Now am focussing on mechanic's and my own observation that AC should be much colder than it is now - mechanic recorded min 14 deg celc with thermormter in the cabin whilst car running. According to Diavia AC should be min of 4 or 5 deg celc. So started tinkering with what are the causes. Its been a year since last topped up so that should be first to do - but i should point out that last year the AC was fully serviced so i wouldn't have had expected gas was an issue 1 yr on.

 

[Dieselman]

Was the measured temperature at the vents witht he air set to recirculation? If not do it again.

 

[KLee]

I will chk and also do the test again myself with my digital thermometer. Oh I didn't know this test officially had to be measured at the vent. I guess that would be the only reference point, makes me think the mechanic would have also done so then. Btw regarding recirculation is another point I am struggling with in MBs - why constantly revert back to outside air after 5 mins? Yes I've heard their thinking fresh air from outside makes driver more alert etc - but I beg to differ - not only is keeping recirculation on allow the cabin air to get colder, I also believe like other car maker that the driver should decide when and what to do, not the car maker decide it for you. I have driven around constantly hitting the recirculation button and the air does get noticeably colder with it on. Also with recirculation ON and cabin colder doesnt the evaporator thermostat then ensure the compressor is taxed less. Anyone know a way of modifying this default recirculation behaviour?

 

[Glenn Smith]

4-5 deg c at the air vents is correct, depending upon ambient temp. any colder will lead to freezing of the evaporator, recirculation time is limited to prevent a lack of oxygen in the cab! The performance of the w202 aircon isn't that spectacular, in my opinion.

 

[KLee]

Thks for finally saying it. Anyone else agree it is less than spectacular and experienced better in cars of same age and history?

 

[Dieselman]

Generally MB aircon isn't that cold. Presumably this is to increase the comfort factor.
Recirc cuts out to a; refresh the cabin air and b; to stop the windows misting up.

So what is your aircon temp at the vents on recirc?

 

[Bazzle]

Generally MB aircon isn't that cold. Presumably this is to increase the comfort factor.
Recirc cuts out to a; refresh the cabin air and b; to stop the windows misting up.

So what is your aircon temp at the vents on recirc?

My 98 SLK is 7 celsius at centre vent on recirc with ambient o/s of 32c whilst driving at 80kph (50mph)
Rises to 12c at idle.

BAzzle

 

[fnkhan68]

i dont know how true this is but i was told that r134 gas is not as effective at cooling as the r12 gas but for the climate of this country is suitable. my car's a/c runs on r12 as it is an old motor but i cant complain with it as it gets really cold.

 

[Birdman]

Thks for finally saying it. Anyone else agree it is less than spectacular and experienced better in cars of same age and history?

I took my first W210 to have the aircon checked when it was still running in. The previous aircon systems to that (RR Corniche;Porsche 928 - sorry) made the M-B system seem anaemic. The M-B mechanic sat in the passenger seat, turnd the temperature to MIN, put the system to recirc and stuck a probe into the vent. After five minutes the digital readout showed 4 degrees C. He said the temperature was restricted to that for reasons of passenger comfort. But the Porsche vents spewed out a fog of white ice-cold air into your face from start up on hot humid days. Let's face it, the M-B system is pushed to cope with a hot English summer's day let alone in the South of France, where I set it to MIN for all journeys under half an hour. The thing barely copes.

In the Middle East I hear aftermarket systems are fitted that cope with the extreme heat.

 

[bagman1971]

Hi
check the wiring from the air con compressor it is a push connector. Bloke may not have pushed on properly. I had this problem with my w202 problem was hole in the condenser. So i fitted new condenser, receiver dryer and got refrigerant system re-filled. Has been ice cold for a year now. Hope this helps. If you were in uk would have a look for you